Cosmology and Nongalactic Astrophysics

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Showing new listings for Wednesday, 17 September 2025

New submissions (showing 11 of 11 entries)

[1] arXiv:2509.12301 [pdf, html, other]

Title: Cosmology with supernova Encore in the strong lensing cluster MACS J0138-2155: Time delays & Hubble constant measurement

J. D. R. Pierel, E. E. Hayes, M. Millon, C. Larison, E. Mamuzic, A. Acebron, A. Agrawal, P. Bergamini, S. Cha, S. Dhawan, J. M. Diego, B. L. Frye, D. Gilman, G. Granata, C. Grillo, M. J. Jee, P. S. Kamieneski, A M. Koekemoer, A. K. Meena, A. B. Newman, M. Oguri, E. Padilla-Gonzalez, F. Poidevin, P. Rosati, S. Schuldt, L. G. Strolger, S. H. Suyu, S. Thorp, A. Zitrin

Comments: Submitted to ApJ. arXiv admin note: text overlap with arXiv:2404.02139

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Multiply-imaged supernovae (SNe) provide a novel means of constraining the Hubble constant ($H_0$). Such measurements require a combination of precise models of the lensing mass distribution and an accurate estimate of the relative time delays between arrival of the multiple images. Only two multiply-imaged SNe, Refsdal and H0pe, have enabled measurements of $H_0$ thus far. Here we detail the third such measurement for SN Encore, a $z=1.95$ SNIa discovered in JWST/NIRCam imaging. We measure the time delay, perform simulations of additional microlensing and millilensing systematics, and combine with the mass models of Suyu et al. in a double-blind analysis to obtain our $H_0$ constraint. Our final time-delay measurement is $\Delta t_{1b,1a}=-39.8_{-3.3}^{+3.9}$ days, which is combined with seven lens models weighted by the likelihood of the observed multiple image positions for a result of $H_0=66.9_{-8.1}^{+11.2} \rm{km} \rm{s}^{-1}\rm{Mpc}^{-1}$. The uncertainty on this measurement could be improved significantly if template imaging is obtained. Remarkably, a sibling to SN Encore (SN "Requiem") was discovered in the same host galaxy, making the MACS J0138.0-2155 cluster the first system known to produce more than one observed multiply-imaged SN. SN Requiem has a fourth image that is expected to appear within a few years, providing an unprecedented decade-long baseline for time-delay cosmography and an opportunity for a high-precision joint estimate of $H_0$.

[2] arXiv:2509.12319 [pdf, html, other]

Title: Cosmology with supernova Encore in the strong lensing cluster MACS J0138-2155: Lens model comparison and H0 measurement

S. H. Suyu, A. Acebron, C. Grillo, P. Bergamini, G. B. Caminha, S. Cha, J. M. Diego, S. Ertl, N. Foo, B. L. Frye, Y. Fudamoto, G. Granata, A. Halkola, M. J. Jee, P. S. Kamieneski, A. M. Koekemoer, A. K. Meena, A. B. Newman, S. Nishida, M. Oguri, P. Rosati, S. Schuldt, A. Zitrin, R. Cañameras, E. E. Hayes, C. Larison, E. Mamuzic, M. Millon, J. D. R. Pierel, L. Tortorelli, H. Wang

Comments: 25 pages, 12 figures, submitted to A&A

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)

MACS J0138-2155 is the only known cluster to strongly lens two supernovae (SNe), Requiem and Encore, from the same host galaxy at z=1.949. We present seven independent mass models of the galaxy cluster built using six software packages. By conducting a blind analysis (no exchanges of results between modeling teams), we quantified uncertainties due to modeling and software. Through HST, JWST and MUSE observations, we assembled high-quality data products, including eight "gold" lensed image systems consisting of 23 images with secure spectroscopic redshifts, and one "silver" system with a likely redshift value. Restricting to the gold images, we obtain overall consistent model predictions of the positions, magnifications and time delays of SN Encore and SN Requiem images, especially for models with $\chi^2 \leq 25$. We predict the appearance of the next images of SNe Encore and Requiem with a time delay of >~3000 days and of ~3700 to 4000 days, respectively, based on a fiducial cosmological model of $H_0 = 70 {\rm\ km\ s^{-1}\ Mpc^{-1}}$ and $\Omega_{\rm m} = 0.3$. We obtain relations between $H_0$ and the time delays of SNe Encore and Requiem. In particular, for $H_0 = 73 {\rm\ km\ s^{-1}\ Mpc^{-1}}$, the four lowest $\chi^2$ models predict SN Requiem to reappear in ~Apr-Dec 2026; for $H_0 = 67 {\rm\ km\ s^{-1}\ Mpc^{-1}}$, in ~Mar-Nov 2027. Using the newly measured time delay between the two detected images of SN Encore by Pierel et al. (submitted) and our mass models, we jointly infer $H_0 = {\rm 66.9^{+11.2}_{-8.1}\ km\ s^{-1}\ Mpc^{-1}}$, where the uncertainty is dominated by that of the time delay. The long delays of the next-appearing SN Requiem and SN Encore images provide excellent opportunities to measure $H_0$ with an uncertainty of 2-3%. Our mass models form the basis for cosmological inference from this unique lens cluster with two strongly lensed SNe. (Abridged)

[3] arXiv:2509.12331 [pdf, html, other]

Title: Lowering the Horizon on Dark Energy: A Late-Time Response to Early Solutions for the Hubble Tension

Tal Adi

Comments: 5 pages, 2 figures, 1 table

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

We present a model-independent null test of the late-time cosmological response to a reduced sound horizon, as typically required by early-universe solutions to the Hubble tension. In this approach, we phenomenologically impose a shorter sound horizon without modeling early-universe physics to isolate its impact on late-time dark energy inference. Using baryon acoustic oscillations (BAO), supernovae (SN), big bang nucleosynthesis (BBN), and local $H_0$ data, while explicitly avoiding CMB anisotropies, we examine how this calibration shift propagates into constraints on the dark energy equation of state. We find that lowering $r_d$ systematically drives the $w_0$-$w_a$ posterior toward less dynamical, quintessence-like behavior, bringing it closer to $\Lambda$CDM. This result underscores that some of the apparent evidence for evolving or phantom-like dark energy may reflect early-universe assumptions rather than genuine late-time dynamics. More broadly, our analysis highlights the importance of carefully disentangling calibration effects from physical evolution in interpreting forthcoming results from DESI and future surveys.

[4] arXiv:2509.12335 [pdf, other]

Title: Phantom Crossing with Quintom Models

L. W. K. Goh, A. N. Taylor

Comments: Submitted to MNRAS, comments welcome

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We develop a two-scalar field quintom model, which utilises both a quintessence-like and a phantom-like scalar field, enabling a smooth and stable transition across the $w=-1$ phantom divide as hinted by recent measurements of Baryonic Acoustic Oscillations (BAO) by the Dark Energy Spectroscopic Instrument (DESI) Data Release 2. We explore a range of initial conditions and potential configurations that facilitate such a phantom-to-quintessence-like crossing, and find that this can be naturally realised with hill-top or cliff-face potentials bound from above. We study how varying these conditions affects the dynamics of the system, calculate the background observables and compare them with DESI, CMB, and Type Ia supernova data, identifying a viable parameter space for our model. In particular, we find that a potential featuring a hyperbolic tangent form can successfully reproduce the desired phantom crossing, although such models can suffer from fine-tuning effects. Finally, we discuss prospects for distinguishing such models with upcoming state-of-the-art cosmological observations.

[5] arXiv:2509.12422 [pdf, html, other]

Title: Search for Quintessence-Like Pseudoscalar Dark Energy Effects on $^{56}\text{Fe}$ Nuclear Transition Energies in Supernova 1991T

Robert D. Orlando, David S. Koltick, Dennis E. Krause

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)

The nature of dark energy remains one of the most important unanswered problems in physics. Here we use gamma-ray spectra from the Type Ia supernova 1991T to constrain the recent evolution of a dynamical pseudoscalar quintessence-like field $Q(t)$. We found that the 1991T gamma rays emitted by the $^{56}\text{Fe}$ nuclei observed by COMPTEL aboard the Compton Gamma Ray Observatory were slightly shifted to lower energies with respect to terrestrial values, with the average fractional energy shift of both the first and second excited states found to be $\delta E/E = -0.006\pm0.008$ including statistical and systematic errors. Assuming that this energy shift is caused by a dynamical QCD axion-like pseudoscalar field $Q(t)$, we find that observed energy deviations are consistent with a fractional rate of change of the pion mass given by $\delta \dot{m_{\pi}}/m_{\pi}=-(6\pm9)\times10^{-11}\text{ yr}^{-1}$. The observed energy deviation was also used to determine the rate of change of the quintessence-like field ($\dot{Q}_0$) for tracking models: $\dot{Q}_{0,max} = (3\pm 4)\times10^7 \text{ GeV/yr}$. Our findings are consistent with the cosmological constant ($\dot{Q}_0 =0$). Furthermore, we have demonstrated how nuclear spectra produced by astrophysical events can be used to inform the nature and behavior of dark energy.

[6] arXiv:2509.13207 [pdf, html, other]

Title: Parity in Composite-Field Galaxy Correlators

Zucheng Gao, Azadeh Moradinezhad Dizgah, Zvonimir Vlah

Comments: 46 pages, 19 figures, 1 table

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Detecting parity violation on cosmological scales would provide a striking clue to new physics. Large-scale structure offers the raw statistical power -- many three-dimensional modes -- to make such tests. However, for scalar observables, like galaxy clustering, the leading parity-sensitive observable is the trispectrum, whose high dimensionality makes the measurement and noise estimation challenging. We present two late-time parity-odd kurto spectra that compress the parity-odd scalar trispectrum into one-dimensional, power-spectrum-like observables. They are built by correlating (i) two appropriately weighted quadratic composite fields, or (ii) a linear and cubic composite field, constructed from dark matter (DM) or galaxy overdensity fields. We develop an FFTLog pipeline for efficient theoretical predictions of the two observables. We then validate the estimators for a specific parity-odd primordial template on perturbative DM field, and on DM and halo fields in full N-body \texttt{Quijote} simulations, with and without parity-odd initial conditions, in real and redshift space. For DM, the variance is dominated by the parity-even contribution -- i.e., the gravitationally induced parity-even trispectrum -- and is efficiently suppressed by phase-matched fiducial subtraction. For halos, discreteness-driven stochasticity dominates and is not appreciably reduced by subtraction; however, optimal weighting and halo-matter cross kurto spectra considerably mitigate this noise and enhance the signal. Using controlled down-sampling of the matter field, we empirically calibrate how the parity-even variance scales with number density and volume, and provide an illustrative forecast for the detectability of parity-odd kurto spectra in a Euclid-like spectroscopic galaxy survey.

[7] arXiv:2509.13220 [pdf, html, other]

Title: Dynamic or Systematic? Bayesian model selection between dark energy and supernova biases

A.N. Ormondroyd, W.J. Handley, M.P. Hobson, A.N. Lasenby

Comments: 8 pages, 5 figures, 2 tables. To be submitted to MNRAS. Comments welcome!

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

DES-5Y supernovae, combined with DESI BAO, appear to favour Chevallier-Polarski-Linder $(w_0, w_a)$ dynamical dark energy over $\Lambda$CDM. arXiv:2408.07175 suggested that this is driven by a systematic in the DES pipeline, which particularly affects the low-redshift supernovae brought in from legacy surveys. It is difficult to investigate these data in isolation, however, as the complicated supernovae pipelines must properly account for selection effects. In this work, we discover that the Bayesian evidence previously found for flexknot dark energy (arXiv:2503.17342) is beaten by a magnitude offset between the low- and high-redshift supernovae. In addition, we find that the possible tension between DES-5Y and DESI is significantly reduced by such an offset. We also take the opportunity to trial Nested Bridge Sampling with Sequential Monte Carlo as an alternative method for calculating Bayes factors.

[8] arXiv:2509.13302 [pdf, html, other]

Title: Comparing Minimal and Non-Minimal Quintessence Models to 2025 DESI Data

Husam Adam, Mark P. Hertzberg, Daniel Jiménez-Aguilar, Iman Khan

Comments: 29 pages, 9 figures, 11 tables

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

In this work we examine the 2025 DESI analysis of dark energy, which suggests that dark energy is evolving in time with an increasing equation of state $w$. We explore a wide range of quintessence models, described by a potential function $V(\varphi)$, including: quadratic potentials, quartic hilltops, double wells, cosine functions, Gaussians, inverse powers. We find that while some provide improvement in fitting to the data, compared to a cosmological constant, the improvement is only modest. We then consider non-minimally coupled scalars which can help fit the data by providing an effective equation of state that temporarily obeys $w<-1$ and then relaxes to $w>-1$. Since the scalar is very light, this leads to a fifth force and to time evolution in the effective gravitational strength, which are both tightly constrained by tests of gravity. For a very narrow range of carefully selected non-minimal couplings we are able to evade these bounds, but not for generic values.

[9] arXiv:2509.13307 [pdf, html, other]

Title: High-Dimensional Bayesian Model Comparison in Cosmology with GPU-accelerated Nested Sampling and Neural Emulators

Toby Lovick, David Yallup, Davide Piras, Alessio Spurio Mancini, Will Handley

Comments: 10 pages 4 figures

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We demonstrate a GPU-accelerated nested sampling framework for efficient high-dimensional Bayesian inference in cosmology. Using JAX-based neural emulators and likelihoods for cosmic microwave background and cosmic shear analyses, our approach provides parameter constraints and direct calculation of Bayesian evidence. In the 39 dimensional $\Lambda$CDM vs $w_0w_a$ shear analysis, we produce Bayes Factors and a robust error bar in just 2 days on a single A100 GPU, without loss of accuracy. Where CPU-based nested sampling can now be outpaced by methods relying on MCMC sampling and decoupled evidence estimation, we demonstrate that with GPU acceleration nested sampling offers the necessary speed-up to put it on equal computational footing with these methods, especially where reliable model comparison is paramount. We put forward both nested and gradient-based sampling as useful tools for the modern cosmologist, where cutting-edge inference pipelines can yield orders of magnitude improvements in computation time.

[10] arXiv:2509.13318 [pdf, html, other]

Title: How Theory-Informed Priors Affect DESI Evidence for Evolving Dark Energy

Michael W. Toomey, Gabriele Montefalcone, Evan McDonough, Katherine Freese

Comments: 16 pages, 7 figures, 2 tables

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

Recent measurements of baryon acoustic oscillations (BAO) from the Dark Energy Spectroscopic Instrument (DESI) have been interpreted to suggest that dark energy may be evolving. In this work, we examine how prior choices affect such conclusions. Specifically, we study the biases introduced by the customary use of uniform priors on the Chevallier-Polarski-Linder (CPL) parameters, $w_0$ and $w_a$, when assessing evidence for evolving dark energy. To do so, we construct theory-informed priors on $(w_0, w_a)$ using a normalizing flow (NF), trained on two representative quintessence models, which learns the distribution of these parameters conditional on the underlying $\Lambda$CDM parameters. In the combined $\textit{Planck}$ CMB + DESI BAO analysis we find that the apparent tension with a cosmological constant in the CPL framework can be reduced from $\sim 3.1\sigma$ to $\sim 1.3\sigma$ once theory-informed priors are applied, rendering the result effectively consistent with $\Lambda$CDM. For completeness, we also analyze combinations that include Type Ia supernova data, showing similar shifts toward the $\Lambda$CDM limit. Taken together, the observed sensitivity to prior choices in these analyses arises because uniform priors - often mischaracterized as "uninformative" - can actually bias inferences toward unphysical parameter regions. Consequently, our results underscore the importance of adopting physically motivated priors to ensure robust cosmological inferences, especially when evaluating new hypotheses with only marginal statistical support. Lastly, our NF-based framework achieves these results by post-processing existing MCMC chains, requiring $\approx 1$ hour of additional CPU compute time on top of the base analysis - a dramatic speedup over direct model sampling that highlights the scalability of this approach for testing diverse theoretical models.

[11] arXiv:2509.13319 [pdf, html, other]

Title: Constraints on Dark Matter Structures around Gaia Black Holes

Nuno P. Branco, Ricardo Z. Ferreira, João G. Rosa, Rodrigo Vicente

Comments: 6 pages, 3 figures

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

We demonstrate that Gaia's detection of stars on wide orbits around black holes opens a new observational window on dark matter structures -- such as scalar clouds and dark matter spikes -- predicted in a range of theoretical scenarios. Using precise radial velocity measurements of these systems, we derive state-of-the-art constraints on dark matter density profiles and particle masses in previously unexplored regions of parameter space. We also test the black hole hypothesis against the alternative of a boson star composed of light scalar fields.

Cross submissions (showing 16 of 16 entries)

[12] arXiv:2509.07069 (cross-list from hep-th) [pdf, html, other]

Title: Consistent Four-derivative Heterotic Truncations and the Kerr-Sen Solution

Liang Ma, Yi Pang, Robert J. Saskowski, Minghao Xia

Comments: 53 pages, 2 figures

Subjects: High Energy Physics - Theory (hep-th); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); Mathematical Physics (math-ph)

Four-derivative heterotic supergravity (without gauge fields) reduced on a $p$-dimensional torus leads to half-maximal supergravity coupled to $p$ vector multiplets, and it is known that removing the vector multiplets is a consistent truncation of the theory. We find a new consistent truncation of four-derivative heterotic supergravity on a torus that keeps the vector multiplets and precisely reproduces the bosonic action of heterotic supergravity (with heterotic gauge fields). We show that both truncations have an $O(d+p,d)$ symmetry when reduced on a $d$-dimensional torus and demonstrate how this embeds in the $O(d+p,d+p)$ symmetry that one gets from reducing on a $(d+p)$-dimensional torus without truncation. We then use our new truncation to obtain four-derivative corrections to the Kerr-Sen solution and compute thermodynamic quantities and multipole moments. Finally, we compare the Kerr-Sen solutions of the actions corresponding to the two different choices of truncation with the Kerr solution, the Kerr-Newman solution, and each other, and show that they have distinct four-derivative multipole structures.

[13] arXiv:2509.07982 (cross-list from hep-ph) [pdf, html, other]

Title: LHAASO Galactic Plane $γ$-rays Strongly Constrain Heavy Dark Matter

Celine Boehm, Ranjan Laha, Tarak Nath Maity

Comments: 29 pages, 8 figures. v1: Comments welcome

Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

LHAASO, a ground-based observatory, is unveiling new frontiers in our understanding of high-energy $\gamma-$rays and cosmic rays. It has recently observed high energy diffuse $\gamma-$rays from the Galactic plane in the TeV-PeV range. For the first time, we analyze this data to search for signatures of heavy decaying and annihilating dark matter in the mass range $10^{5}-10^{11}$ GeV. We compute the expected photon flux from both Galactic and extragalactic dark matter, incorporating attenuation due to photon pair production. For the Galactic contribution, we include both prompt photons and secondary photons produced via inverse Compton scattering, accounting for electron/positron propagation. For the extragalactic component, in addition to the prompt and inverse Compton contributions, we also include cascade photons arising from inverse Compton scattering of pair-produced electrons and positrons. By combining all these contributions, we derive constraints on the dark matter parameter space. Our bounds for various two body Standard Model final states are strongest to date. This underscore LHAASO's capability to discover the nature of heavy dark matter.

[14] arXiv:2509.11647 (cross-list from hep-th) [pdf, html, other]

Title: Bumblebee vector-tensor dark energy

Carsten van de Bruck, Mohammad Ali Gorji, Nils A. Nilsson, Masahide Yamaguchi

Comments: 27 pages, no figures

Subjects: High Energy Physics - Theory (hep-th); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

Bumblebee models, a class of vector-tensor theories in which a vector field acquires a nonzero vacuum expectation value that spontaneously breaks spacetime symmetries, are ubiquitous in the literature. In this paper, we highlight several often-overlooked properties of these models by analyzing their cosmological perturbations. We show that a non-minimal coupling to gravity is essential for the stability of the setup. However, avoiding propagation of a ghost mode then requires imposing a relation between the coupling coefficients, known as the degeneracy condition, which reduces the bumblebee model to a subset of generalized Proca theories with a marginal non-minimal operator. By imposing the degeneracy condition, the vector field becomes non-dynamical at the background level, and the form of its potential is completely fixed in vacuum. We show that the vacuum expectation value of the vector field can drive a de Sitter solution, for which the effects of the non-minimal coupling are negligible at the background level but provide essential order-one corrections to the sound speed of the scalar mode, keeping the setup weakly coupled at the level of perturbations. Treating this stealth de Sitter solution as a dark energy candidate, we study its coupling to matter and find the effective gravitational coupling for the matter density contrast in the quasi-static regime. At the level of perturbations, the system behaves differently from $\Lambda$CDM, providing a potential observational signature to distinguish the two models.

[15] arXiv:2509.12309 (cross-list from hep-ph) [pdf, html, other]

Title: Taming the dark photon production via a non-minimal coupling to gravity

Oleg Lebedev, Jong-Hyun Yoon

Comments: 8 pages, 2 figures

Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Inflationary production of massive dark photons with non-minimal couplings to gravity shows surprising growth at large momenta. These couplings appear in the effective low energy description of a more fundamental theory. We find that the growth is absent in explicit gauge invariant UV-complete models. Such completions are also free of "ghost" instabilities, which often appear in the effective models.

[16] arXiv:2509.12313 (cross-list from astro-ph.GA) [pdf, html, other]

Title: DELVE Milky Way Satellite Census I: Satellite Population and Survey Selection Function

C. Y. Tan, A. Drlica-Wagner, A. B. Pace, W. Cerny, E. O. Nadler, A. Doliva-Dolinsky, T. S. Li, J. D. Simon, A. K. Vivas, A. R. Walker, M. Adamów, D. Anbajagane, K. Bechtol, J. L. Carlin, Q. O. Casey, C. Chang, A. Chaturvedi, T.-Y. Cheng, A. Chiti, Y. Choi, D. Crnojević, P. S. Ferguson, R. A. Gruendl, A. P. Ji, G. Limberg, G. E. Medina, B. Mutlu-Pakdil, K. Overdeck, V. M. Placco, N. E. D. Noël, A. H. Riley, D. J. Sand, J. Sharp, N. F. Sherman, G. S. Stringfellow, R. H. Wechsler, M. Aguena, S. Allam, O. Alves, D. Bacon, D. Brooks, D. L. Burke, R. Camilleri, J. A. Carballo-Bello, A. Carnero Rosell, J. Carretero, L. N. da Costa, M. E. da Silva Pereira, T. M. Davis, J. De Vicente, S. Desai, S. Everett, B. Flaugher, J. Frieman, J. García-Bellido, D. Gruen, G. Gutierrez, K. Herner, S. R. Hinton, D. L. Hollowood, D. J. James, K. Kuehn, O. Lahav, S. Lee, J. L. Marshall, C. E. Martínez-Vázquez, P. Massana, J. Mena-Fernández, R. Miquel, J. Muir, J. Myles, R. L. C. Ogando, A. A. Plazas Malagón, A. Porredon, E. Sanchez, D. Sanchez Cid, I. Sevilla-Noarbe, M. Smith, E. Suchyta, M. E. C. Swanson, C. To, E. J. Tollerud, D. L. Tucker, V. Vikram, N. Weaverdyck, M. Yamamoto, A. Zenteno (DELVE and DES Collaboration)

Comments: 35 pages, 13 figures, 8 tables; Submitted to AAS Journals

Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The properties of Milky Way satellite galaxies have important implications for galaxy formation, reionization, and the fundamental physics of dark matter. However, the population of Milky Way satellites includes the faintest known galaxies, and current observations are incomplete. To understand the impact of observational selection effects on the known satellite population, we perform rigorous, quantitative estimates of the Milky Way satellite galaxy detection efficiency in three wide-field survey datasets: the Dark Energy Survey Year 6, the DECam Local Volume Exploration Data Release 3, and the Pan-STARRS1 Data Release 1. Together, these surveys cover $\sim$13,600 deg$^2$ to $g \sim 24.0$ and $\sim$27,700 deg$^2$ to $g \sim 22.5$, spanning $\sim$91% of the high-Galactic-latitude sky ($|b| \geq 15^\circ$). We apply multiple detection algorithms over the combined footprint and recover 49 known satellites above a strict census detection threshold. To characterize the sensitivity of our census, we run our detection algorithms on a large set of simulated galaxies injected into the survey data, which allows us to develop models that predict the detectability of satellites as a function of their properties. We then fit an empirical model to our data and infer the luminosity function, radial distribution, and size-luminosity relation of Milky Way satellite galaxies. Our empirical model predicts a total of $265^{+79}_{-47}$ satellite galaxies with $-20 \leq M_V \leq 0$, half-light radii of $15 \leq r_{1/2} (\rm pc) \leq 3000$, and galactocentric distances of $10 \leq D_{\rm GC} (\rm kpc) \leq 300$. We also identify a mild anisotropy in the angular distribution of the observed galaxies, at a significance of $\sim$$2\sigma$, which can be attributed to the clustering of satellites associated with the LMC.

[17] arXiv:2509.12333 (cross-list from hep-ph) [pdf, html, other]

Title: Leptogenesis from Dark Matter Coannihilation

Simran Arora, Debasish Borah, Arnab Dasgupta, P. S. Bhupal Dev, Devabrat Mahanta

Comments: 29 pages, 17 captioned figures, 1 table

Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We propose a minimal extension of the type-I seesaw model to realise leptogenesis from the co-annihilation of dark sector particles. The type-I seesaw model is extended with a singlet fermion and two singlet scalars charged under a $Z_{2}$ symmetry. The $Z_{2}$-odd singlet scalar is the dark matter candidate. Here the usual type-I seesaw mechanism generates neutrino mass, and a net lepton asymmetry is generated from the co-annihilation of the dark matter and the $Z_2$-odd singlet fermion. The $Z_{2}$-even singlet scalar is important in dark matter phenomenology. Successful leptogenesis is possible at TeV-scale, unlike the vanilla case. This minimal extension provides an elegant explanation of successful leptogenesis with direct connection to the dark matter abundance in the Universe.

[18] arXiv:2509.12352 (cross-list from astro-ph.GA) [pdf, html, other]

Title: Predicting stellar collision outcomes of main sequence stars

Pau Amaro Seoane

Comments: Submitted, 11 pages

Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Stellar collisions in dense galactic nuclei might play an important role in fueling supermassive black holes (SMBHs) and shaping their environments. The gas released during these collisions can contribute to SMBH accretion, influencing phenomena such as active galactic nuclei and tidal disruption events of the remnants. We address the challenge of rapidly and accurately predicting the outcomes of stellar collisionsincluding remnant masses and unbound gasacross a broad parameter space of initial conditions. Existing smoothed-particle-hydrodynamic (SPH) simulation techniques, while detailed, are too resource-intensive for exploratory studies or real-time applications. We develop a machine learning framework trained on a dataset of $\sim 16,000$ SPH simulations of main-sequence star collisions. By extracting physically meaningful parameters (e.g., masses, radii, impact parameters, and virial ratios) and employing gradient-boosted regression trees with Huber loss, we create a model that balances accuracy and computational efficiency. The method includes logarithmic transforms to handle dynamic ranges and regularization to ensure physical plausibility. The model achieves predictions of collision outcomes (remnant masses, and unbound mass) with very low mean absolute errors respect to the typical mass scale. It operates in fractions of a second, enabling large-scale parameter studies and real-time applications. Parameter importance analysis reveals that the impact parameter and the relative velocity dominate outcomes, aligning with theoretical expectations. Our approach provides a scalable tool for studying stellar collisions in galactic nuclei. The rapid predictions facilitate investigations into gas supply for SMBH accretion and the cumulative effects of collisions over cosmic time, particularly relevant to address the growth of SMBHs.

[19] arXiv:2509.12414 (cross-list from hep-ph) [pdf, html, other]

Title: Probing Flavour Deconstruction via Primordial Gravitational Waves

Noemi Fabri, Gino Isidori, Davide Racco

Comments: 8 pages, 5 figures

Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We study the production of primordial gravitational waves (GWs) from first-order phase transitions (FOPTs) in extensions of the Standard Model based on Flavour Deconstruction (FD). The link fields inherent to FD generically form a rich scalar sector, with sizeable couplings at the TeV scale, providing natural conditions for strong FOPTs and correspondingly large GW emission. We identify the key parameters controlling the GW spectrum and enabling its detection at future GW observatories. In particular, we find that while FD scenarios can yield detectable signals, the resulting spectra typically peak at higher frequencies than the millihertz range. As a consequence, a positive observation at LISA is possible but not guaranteed, while the signal falls in the range of mid-band proposals, making FD models an intriguing target for upcoming GW searches.

[20] arXiv:2509.12520 (cross-list from hep-ph) [pdf, html, other]

Title: On the (Im)possibility of Electrically Charged Planck Relics

Stefano Profumo

Comments: 24 pages, 3 figures, comments welcome

Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)

I revisit whether black-hole remnants, from sub-Planckian compact objects to Planck relics and up to (super)massive black holes, can preserve Standard-Model (SM) electric charge. Two exterior-field mechanisms -- Coulomb-focused capture from ambient media and QED Schwinger pair production -- robustly neutralize such objects across cosmic history. I first derive the general capture rate including both Coulomb and gravitational focusing, and sum the stepwise discharge time in closed form via the trigamma function, exhibiting transparent Coulomb- and gravity-dominated limits. I then integrate the Schwinger rate over the near-horizon region to obtain an explicit $\dot Q(Q)$ law: discharge proceeds until the horizon field falls below $E_{\rm crit}$, leaving a residual charge $Q_{\rm stop}^{(e)}\!\propto\! r_h^2$ that is $\ll e$ for Planck radii. Mapping the mass dependence from sub-Planckian to astrophysical scales, I also analyze dark-sector charges with heavy carriers (including kinetic mixing and massive mediators). In a conservative ``no-Schwinger'' limit where vacuum pair creation is absent, cumulative ambient exposures alone force discharge of any integer SM charge. Three possible loopholes remain. (i) A fine-tuned SM corner in which the relic sits arbitrarily close to Reissner-Nordström extremality so greybody factors suppress charged absorption, while Schwinger pair creation is absent due to Planck-scale physics. (ii) Charge relocated to a hidden $U(1)_D$ with no light opposite carriers, e.g. if the lightest state is very heavy and/or kinetic mixing with $U(1)_{\rm EM}$ is vanishingly small. (iii) Discrete or topological charges rather than ordinary SM electric charge. Outside these cases, the conclusion is robust: within SM electromagnetism, charged black-hole relics neutralize efficiently and cannot retain charge over cosmological times.

[21] arXiv:2509.12929 (cross-list from gr-qc) [pdf, html, other]

Title: Quantum Computing Tools for Fast Detection of Gravitational Waves in the Context of LISA Space Mission

Maria-Catalina Isfan, Laurentiu-Ioan Caramete, Ana Caramete, Daniel Tonoiu, Alexandru Nicolin-Zaczek

Comments: Submitted to Classical and Quantum Gravity

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Instrumentation and Methods for Astrophysics (astro-ph.IM); Data Analysis, Statistics and Probability (physics.data-an)

The field of gravitational wave (GW) detection is progressing rapidly, with several next-generation observatories on the horizon, including LISA. GW data is challenging to analyze due to highly variable signals shaped by source properties and the presence of complex noise. These factors emphasize the need for robust, advanced analysis tools. In this context, we have initiated the development of a low-latency GW detection pipeline based on quantum neural networks (QNNs). Previously, we demonstrated that QNNs can recognize GWs simulated using post-Newtonian approximations in the Newtonian limit. We then extended this work using data from the LISA Consortium, training QNNs to distinguish between noisy GW signals and pure noise. Currently, we are evaluating performance on the Sangria LISA Data Challenge dataset and comparing it against classical methods. Our results show that QNNs can reliably distinguish GW signals embedded in noise, achieving classification accuracies above 98\%. Notably, our QNN identified 5 out of 6 mergers in the Sangria blind dataset. The remaining merger, characterized by the lowest amplitude, highlights an area for future improvement in model sensitivity. This can potentially be addressed using additional mock training datasets, which we are preparing, and by testing different QNN architectures and ansatzes.

[22] arXiv:2509.12998 (cross-list from astro-ph.HE) [pdf, html, other]

Title: Probing the millisecond pulsar origin of the GeV excess in the Galactic Centre with LISA

Valeriya Korol, Andrei Igoshev

Comments: Submitted to A&A. Comments are welcome

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

The GeV $\gamma$-ray excess observed towards the Galactic Centre remains unexplained. While dark matter annihilation has long been considered a leading interpretation, an alternative scenario involving a large population of millisecond pulsars has not been ruled out. Testing this hypothesis with electromagnetic observations is difficult, as pulsar searches in the bulge are strongly affected by scattering, high sky temperature, and source confusion. We investigate whether gravitational-wave observations with the Laser Interferometer Space Antenna (LISA) could provide an independent probe of the millisecond pulsar binary population in the Galactic bulge.
We construct synthetic populations of millisecond pulsar-white dwarf binaries under two illustrative formation scenarios: an accreted scenario, in which systems are deposited by disrupted globular clusters, and an in situ scenario, in which binaries form through isolated binary evolution. In both cases, only $10^{-5}$--$10^{-4}$ of the underlying bulge population is detectable by LISA. Nevertheless, even a few detections would imply tens to hundreds of thousands of unseen systems. Accreted binaries are expected to have lower chirp masses ($\sim$0.4 M$_\odot$), while in situ binaries produce more massive companions ($\sim$0.9 M$_\odot$).
LISA will measure binary frequencies with high precision, but chirp masses can only be determined for the most massive or highest-frequency systems. Distinguishing millisecond pulsar binaries from the far more numerous double white dwarfs will be challenging, though LISA detections could provide valuable targets for follow-up with the Square Kilometre Array, enabling a critical test of the millisecond pulsar origin of the $\gamma$-ray excess.

[23] arXiv:2509.13010 (cross-list from astro-ph.IM) [pdf, html, other]

Title: Capturing System Drift with Time Series Calibration for Global 21-cm Cosmology Experiments

Christian J. Kirkham, Dominic J. Anstey, Eloy de Lera Acedo

Comments: 9 pages, 6 figures

Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

To achieve the sensitivity required to detect signals from neutral hydrogen from the Cosmic Dawn and Epoch of Reionisation it is critical to have a well-calibrated instrument which has a stable calibration over the course of the observation. Previous calibration methods do not explicitly use the time information available and make assumptions on the impedance matching of the reference sources. Here we present a new calibration method based on noise wave parameters which fits a calibration solution over time and frequency to the data, interpolating the solutions to the times at which the antenna is being measured. To test this method we simulate a dataset using measurements of the REACH receiver, modelling a low noise amplifier which is drifting over time. Fitting a polynomial surface in frequency and time to the simulated data demonstrates that we can remove the drift in the calibrated solution over time but leaves a chromatic residual. We further show that we can remove assumptions on the reflection coefficients of the reference noise source and the cold load, reducing degeneracies in the parameter fits. Applying this new calibration equation and surface fitting method to the simulated data removes the chromatic residual in the calibrated spectrum and recovers the parameters to within 0.06% of the truth and a 97% reduction in the RMSE of the spectrum of the validation source compared with previous calibration methods. For two parameters we report up to six times smaller fit error after the degeneracies are removed from the time-based calibration.

[24] arXiv:2509.13098 (cross-list from hep-ph) [pdf, html, other]

Title: Cogenesis of baryon and lepton number asymmetries matching the EMPRESS Data

Kyu Jung Bae, Arghyajit Datta, Rinku Maji, Wan-Il Park

Comments: 19 pages, 4 figures

Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We show that a simple supersymmetric $U(1)_{B-L}$ extension of the standard model can explain simultaneously the large electron neutrino asymmetry hinted by the recent EMPRESS data as well as the observed tiny baryon number asymmetry via the resonant leptogenesis mechanism. The condensation of $B-L$ Higgs dominating the universe at its decay is the sole source for these generation processes. Here, the infrequent decays of the $B-L$ Higgs to heavy right handed neutrinos and successive prompt decays of these right handed neutrinos around the electroweak phase transition produce the observed baryon number asymmetry, while the complete decay of the same $B-L$ Higgs at a later epoch leads to a large lepton number asymmetry. The right amounts of both asymmetries are found to be obtained for the symmetry-breaking scale $v_\phi \sim 10^{10}~{\rm GeV}$. Moreover, in a close connection to the positivity of both asymmetries, seemingly only the normal mass hierarchy of light neutrino species works. Finally, the gravitational wave background from the topologically stable strong type-I cosmic strings, generated from the breaking of $U(1)_{B-L}$ symmetry, can be within the reach of future experiments such as ultimate DECIGO.

[25] arXiv:2509.13292 (cross-list from hep-ph) [pdf, html, other]

Title: Revisiting axion dark matter with nonlinear transitions

Max Miyazaki, Yuma Narita, Deheng Song, Nemin Yaginuma, Wen Yin

Comments: 25pages, 7figures

Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Recently, two of the present authors showed that even when the axion momentum is much smaller than its mass, the axion can still behave like radiation if its energy density greatly exceeds the maximum potential energy set by the cosine-type potential. As the energy density redshifts down to the potential scale, a nonlinear transition occurs, during which the axion's adiabatic invariant is not conserved. In this paper, we revisit the analysis of axion dark matter by incorporating the effects of this nonlinear transition through a precise study of the axion spectrum. We demonstrate that in the parameter region with a relatively small decay constant, often favored in axion search experiments, special care is required when estimating the axion abundance and spectrum. We also highlight a scenario in which axions are produced through the stimulated decay of a modulus, a situation that may naturally arise in the string axiverse, where the nonlinear transition occurs across a wide parameter region. Furthermore, we discuss related phenomena, including QCD axion dark matter, the formation of axion clumps such as miniclusters and axion stars, gravitational wave production, and formation of primordial black holes as dark matter.

[26] arXiv:2509.13308 (cross-list from astro-ph.GA) [pdf, html, other]

Title: VAR-PZ: Constraining the Photometric Redshifts of Quasars using Variability

S. Satheesh Sheeba, R. J. Assef, T. Anguita, P. Sánchez-Sáez, R. Shirley, T. T. Ananna, F. E. Bauer, A. Bobrick, C. G. Bornancini, S. E. I. Bosman, W. N. Brandt, D. De Cicco, B. Czerny, M. Fatović, K. Ichikawa, D. Ilić, A. B. Kovačević, G. Li, M. Liao, A. Rojas-Lilayú, M. Marculewicz, D. Marsango, C. Mazzucchelli, T. Mkrtchyan, S. Panda, A. Peca, B. Rani, C. Ricci, G. T. Richards, M. Salvato, D. P. Schneider, M. J. Temple, F. Tombesi, W. Yu, I. Yoon, F. Zou

Comments: 15 Pages, 11 figures, 2 tables, Submitted to A&A

Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The Vera C. Rubin Observatory LSST is expected to discover tens of millions of new Active Galactic Nuclei (AGNs). The survey's exceptional cadence and sensitivity will enable UV/optical/NIR monitoring of a significant fraction of these objects. The unprecedented number of sources makes spectroscopic follow-up for the vast majority of them unfeasible in the near future, so most studies will have to rely on photometric redshifts estimates which are traditionally much less reliable for AGN than for inactive galaxies. This work presents a novel methodology to constrain the photometric redshift of AGNs that leverages the effects of cosmological time dilation, and of the luminosity and wavelength dependence of AGN variability. Specifically, we assume that the variability can be modeled as a damped random walk (DRW) process, and adopt a parametric model to characterize the DRW timescale ($\tau$) and asymptotic amplitude of the variability (SF$_\infty$) based on the redshift, the rest-frame wavelength, and the AGN luminosity. We construct variability-based photo-$z$ priors by modeling the observed variability using the expected DRW parameters at a given redshift. These variability-based photometric redshift (VAR-PZ) priors are then combined with traditional SED fitting to improve the redshift estimates from SED fitting.
Validation is performed using observational data from the SDSS, demonstrating significant reduction in catastrophic outliers by more than 10% in comparison with SED fitting techniques and improvements in redshift precision. The simulated light curves with both SDSS and LSST-like cadences and baselines confirm that, VAR-PZ will be able to constrain the photometric redshifts of SDSS-like AGNs by bringing the outlier fractions down to below 7% from 32% (SED-alone) at the end of the survey.

[27] arXiv:2509.13322 (cross-list from hep-ph) [pdf, html, other]

Title: Axion-photon conversion in transient compact stars: Systematics, constraints, and opportunities

Damiano F. G. Fiorillo, Ángel Gil Muyor, Hans-Thomas Janka, Georg G. Raffelt, Edoardo Vitagliano

Comments: 77 pages, 13 figures

Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

We study magnetic conversion of ultra-relativistic axion-like particles (ALPs) into photons in compact-star environments, focusing on the hot, transient conditions of core-collapse supernova (SN) remnants and neutron-star mergers (NSMs). We address previously overlooked uncertainties, particularly the suppression caused by ejected matter near the stellar surface, a region crucial to the conversion process. We derive analytical expressions for the transition rate; they reveal the influence of key parameters and their uncertainties. We update constraints using historical gamma-ray data from SN~1987A and find $g_{a\gamma}<5\times10^{-12}~{\rm GeV}^{-1}$ for $m_a\lesssim10^{-9}$ meV. We also forecast sensitivities for a future Galactic SN and for NSMs, assuming observations with Fermi-LAT or similar gamma-ray instruments. We distinguish ALPs -- defined as coupling only to photons and produced via Primakoff scattering -- from axions, which also couple to nucleons and emerge through nuclear bremsstrahlung. We omit pionic axion production due to its large uncertainties and inconsistencies, though it could contribute comparably to bremsstrahlung under optimistic assumptions. For the compact sources, we adopt time-averaged one-zone models, guided by numerical simulations, to enable clear and reproducible parametric studies.

Replacement submissions (showing 14 of 14 entries)

[28] arXiv:2410.06962 (replaced) [pdf, html, other]

Title: KiDS-Legacy: Covariance validation and the unified OneCovariance framework for projected large-scale structure observables

Robert Reischke, Sandra Unruh, Marika Asgari, Andrej Dvornik, Hendrik Hildebrandt, Benjamin Joachimi, Lucas Porth, Maximilian von Wietersheim-Kramsta, Jan Luca van den Busch, Benjamin Stölzner, Angus H. Wright, Ziang Yan, Maciej Bilicki, Pierre Burger, Nora Elisa Chisari, Joachim Harnois-Deraps, Christos Georgiou, Catherine Heymans, Priyanka Jalan, Shahab Joudaki, Konrad Kuijken, Shun-Sheng Li, Laila Linke, Constance Mahony, Davide Sciotti, Tilman Tröster, Mijin Yoon

Comments: 37 pages, 11 figures, published in A&A, code available at this https URL

Journal-ref: A&A 699, A124 (2025)

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We introduce OneCovariance, an open-source software designed to accurately compute covariance matrices for an arbitrary set of two-point summary statistics across a variety of large-scale structure tracers. Utilising the halo model, we estimated the statistical properties of matter and biased tracer fields, incorporating all Gaussian, non-Gaussian, and super-sample covariance terms. The flexible configuration permits user-specific parameters, such as the complexity of survey geometry, the halo occupation distribution employed to define each galaxy sample, or the form of the real-space and/or Fourier space statistics to be analysed. We illustrate the capabilities of OneCovariance within the context of a cosmic shear analysis of the final data release of the Kilo-Degree Survey (KiDS-Legacy). Upon comparing our estimated covariance with measurements from mock data and calculations from independent software, we ascertain that OneCovariance achieves accuracy at the per cent level. When assessing the impact of ignoring complex survey geometry in the cosmic shear covariance computation, we discover misestimations at approximately the $10\%$ level for cosmic variance terms. Nonetheless, these discrepancies do not significantly affect the KiDS-Legacy recovery of cosmological parameters. We derive the cross-covariance between real-space correlation functions, bandpowers, and COSEBIs, facilitating future consistency tests among these three cosmic shear statistics. Additionally, we calculate the covariance matrix of photometric-spectroscopic galaxy clustering measurements, validating the jackknife covariance estimates for calibrating KiDS-Legacy redshift distributions. The OneCovariance can be found on GitHub, together with comprehensive documentation and examples.

[29] arXiv:2410.07412 (replaced) [pdf, html, other]

Title: Circumventing Cosmic Variance via Remote Quadrupole Measurements

Arsalan Adil, Reid Koutras, Emory F. Bunn

Comments: Changes in v2: As suggested by an anonymous referee, we now calculate the Fisher matrix for a more general parameterization with two parameters and marginalize, instead of fixing, the additional parameter. All figures and values have been updated with the new results

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)

A number of important cosmological questions can be addressed only by probing perturbation modes on the largest accessible scales. One promising probe of these modes is the Kamionkowski-Loeb effect, i.e., the polarization induced in the cosmic microwave background (CMB) by Thomson scattering in galaxy clusters, which is proportional to the CMB quadrupole measured at the cluster's location and look-back time. We develop a Fisher formalism for assessing the amount of new information that can be obtained from a future remote quadrupole survey. To demonstrate the constraining power of such a survey, we apply our formalism to a model that suppresses the primordial power spectrum on large scales but is poorly constrained with existing CMB data. We find that the constraints can be improved by over $3\sigma$ for a survey that measures around 100 clusters over $20\%$ of the sky with a signal-to-noise ratio of $3$. In the most optimistic case with a low-noise survey with dense full-sky coverage and only a single degree of freedom in the theory, the constraint improves to over $7\sigma$ beyond local CMB data. Our formalism, which is based in real space rather than harmonic space, can be used to explore a wide range of survey designs, and our results paint an optimistic picture for the utility of remote quadrupole measurements to probe physics on the largest observable scales in the Universe.

[30] arXiv:2504.09523 (replaced) [pdf, html, other]

Title: Decaying vacuum energy, matter creation and cosmic acceleration

Lokesh Chander, C P Singh

Comments: 42 pages, 20 figures

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

We discuss an interacting dark sector model featuring decaying vacuum energy and dark matter empowered by gravitationally induced matter creation. Motivated by quantum field theoretic considerations of vacuum decay and adiabatic particle production, we analyse both the background dynamics and the growth rate of perturbations. The model is confronted with diverse datasets, including Cosmic Chronometers, Pantheon Type Ia Supernovae, Baryon Acoustic Oscillations, Cosmic Microwave Background distance priors, weighted linear growth rate measurements and an $H_0$ prior, with parameter estimation performed via Markov Chain Monte Carlo (MCMC) methods. Model comparison is carried out using the Akaike and Deviance Information Criterion. Our results show a consistent transition from a decelerated to an accelerated expansion phase, with present Hubble parameter estimates lying between the Planck and SH0ES values, thereby easing the Hubble tension. The structure growth parameter $S_8$ is also compatible with Planck 2018 and recent weak lensing surveys. A thermodynamic analysis confirms consistency with the generalized second law, and including Casimir contributions provides further insights into the model's dynamics. Overall, the proposed model effectively captures the Universe's evolution at both theoretical and observational levels.}

[31] arXiv:2506.04162 (replaced) [pdf, html, other]

Title: The effective running Hubble constant in SNe Ia as a marker for the dark energy nature

E. Fazzari, M.G. Dainotti, G. Montani, A. Melchiorri

Comments: 36 pages, 9 figures; discussion expanded, results updated and references added; matches the version published in JHEAP at this https URL

Journal-ref: JHEAP 49, 100459 (2026)

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We propose a new method that reveal the nature of dark energy (DE) evolution. Specifically, the method consists of studying the evolving trend regarding the effective running Hubble constant: when it increases, it indicates a quintessence nature, and when it decreases, it reveals a phantom behavior. Within the framework of the dark energy models we analyze three parameterizations: the $w$CDM model, a reduced Chevallier-Polarski-Linder (CPL) model and a new theoretical model based on the possible creation of dark energy by the time-varying gravitational field of the expanding Universe. For each DE model, we construct a theoretical effective running Hubble constant, i.e. a function of the redshift, which highlights the difference between modified dynamics and the $\Lambda$CDM-one. Furthermore, these dark energy models are compared to the phenomenological model of a decreasing trend of the Hubble constant as a function of the redshift, called the power-law model (PL) and the $\Lambda$CDM one. These three theoretical functions are fitted against the binned SNe Ia data samples, i.e. the Pantheon and the Master samples, the latter being a collection of SNe Ia from 4 catalogs: Dark Energy Survey (DES), PantheonPlus, Pantheon and Joint Lightcurve Analysis (JLA), without duplicated SNe Ia, called the Master sample. The main result of our study is that the phenomenological PL model is statistically favored compared to the other proposed scenarios, both for the Pantheon and the Master samples. At this stage, the SNe Ia data do not indicate that the evolution of dark energy models among the studied ones is favored respect to the $\Lambda$CDM. Nevertheless, the binned Pantheon sample allows for a discrimination of the nature of dark energy at least at the $1\,\sigma$ level via the fit of the effective running Hubble constant.

[32] arXiv:2506.11943 (replaced) [pdf, html, other]

Title: Calibrating baryonic effects in cosmic shear with external data in the LSST era

Amy Wayland, David Alonso, Matteo Zennaro

Comments: 17 pages, 13 figures

Journal-ref: Monthly Notices of the Royal Astronomical Society (MNRAS) September 2025

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Cosmological constraints derived from weak lensing (WL) surveys are limited by baryonic effects, which suppress the non-linear matter power spectrum on small scales. By combining WL measurements with data from external tracers of the gas around massive structures, it is possible to calibrate baryonic effects and, therefore, obtain more precise cosmological constraints. In this study, we generate mock data for a Stage-IV weak lensing survey such as the Legacy Survey of Space and Time (LSST), X-ray gas fractions, and stacked kinetic Sunyaev-Zel'dovich (kSZ) measurements, to jointly constrain cosmological and astrophysical parameters describing baryonic effects (using the Baryon Correction Model - BCM). First, using WL data alone, we quantify the level to which the BCM parameters will need to be constrained to recover the cosmological constraints obtained under the assumption of perfect knowledge of baryonic feedback. We identify the most relevant baryonic parameters and determine that they must be calibrated to a precision of $\sim 10$-$20\%$ to avoid significant degradation of the fiducial WL constraints. We forecast that long-term X-ray data from $\sim 5000$ clusters should be able to reach this threshold for the parameters that characterise the abundance of hot virialised gas. Constraining the distribution of ejected gas presents a greater challenge, however, but we forecast that long-term kSZ data from a CMB-S4-like experiment should achieve the level of precision required for full self-calibration.

[33] arXiv:2509.11305 (replaced) [pdf, html, other]

Title: The SRG/eROSITA All-Sky Survey $J$-Band Follow-Up Observations for Selected High-Redshift Galaxy Cluster Candidates

N. Zimmermann, M. Kluge, S. Grandis, T. Schrabback, F. Balzer, E. Bulbul, J. Comparat, B. Csizi, V. Ghirardini, H. Jansen, F. Kleinebreil, A. Liu, A. Merloni, M. E. Ramos-Ceja, J. Sanders, X. Zhang, P. Aschenbrenner, F. Enescu, S. Keiler, M. Märk, M. Rinner, P. Schweitzer, E. Silvestre-Rosello, L. Stepman

Comments: 24 pages, 13 figures, 8 tables, submitted to A&A, changed affiliations, added acknowledgement

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We select galaxy cluster candidates from the high-redshift (BEST_Z > 0.9) end of the first SRG/eROSITA All-Sky Survey (eRASS1) galaxy cluster catalogue, for which we obtain moderately deep J-band imaging data with the OMEGA2000 camera at the 3.5m telescope of the Calar Alto Observatory. We include J-band data of four additional targets obtained with the three-channel camera at the 2m Fraunhofer telescope at the Wendelstein Observatory. We complement the new J-band photometric catalogue with forced photometry in the i- and z-bands of the tenth data release of the Legacy Survey (LSDR10) to derive the radial colour distribution around the eRASS1 clusters. Without assuming a priori to find a cluster red sequence at a specific colour, we try to find a radially weighted colour over-density to confirm the presence of high-redshift optical counterparts for the X-ray emission. We compare our confirmation with optical properties derived in earlier works based on LSDR10 data to refine the existing high-redshift cluster confirmation of eROSITA-selected clusters. We attempt to calibrate the colour-redshift-relation including the new J-band data by comparing our obtained photometric redshift estimate with the spectroscopic redshift of a confirmed, optically selected, high-redshift galaxy cluster. We confirm 9 out of 18 of the selected galaxy cluster candidates with a radial over-density of similar coloured galaxies for which we provide a photometric redshift estimate. We can report an increase in the relative colour measurement precision from 8% to 4% when including J-band data. In conclusion, our findings indicate a not insignificant spurious contaminant fraction at the high-redshift end (BEST_Z > 0.9) of the eROSITA/eRASS1 galaxy cluster catalogue, as well as it underlines the necessity for wide and deep near infrared imaging data for confirmation and characterisation of high-$z$ galaxy clusters.

[34] arXiv:2412.03406 (replaced) [pdf, html, other]

Title: The Outskirt Stellar Mass of Low-Redshift Massive Galaxies is an Excellent Halo Mass Proxy in Illustris/IllustrisTNG Simulations

Shuo Xu, Song Huang, Alexie Leauthaud, Benedikt Diemer, Katya Leidig, Carlo Cannarozzo, Conghao Zhou

Comments: 21 pages, 8 figures, accepted for publication in ApJ

Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Recent observations suggest that the extended stellar halos of low-redshift massive galaxies are tightly connected to the assembly of their dark matter halos. In this paper, we use the Illustris, IllustrisTNG100, and IllustrisTNG300 simulations to compare how different stellar aperture masses trace halo mass. For massive central galaxies ($M_\star\geq 10^{11.2}M_\odot$), we find that a 2D outskirt stellar mass measured between 50 to 100 kpc ($M_{\star,[50,100]}$) consistently outperforms other aperture-based stellar masses. We further show that $M_{\star,[50,100]}$ correlates better with halo mass than the total amount of accreted stars (the ex situ mass), which suggests that not all accreted stars connect to halo assembly equally. While the galaxy formation recipes are different between Illustris and IllustrisTNG100, the two simulations yield consistent ex situ outskirt fractions for massive galaxies (about 70% in $M_{\star,[50,100]}$). These results demonstrate the potential of using the outskirt stellar mass to deepen our understanding of galaxy-halo connection in massive dark matter halos and trace dark matter halos better.

[35] arXiv:2502.20449 (replaced) [pdf, html, other]

Title: Cosmological Stasis from Field-Dependent Decay

Fei Huang, V. Knapp-Perez

Comments: 35 pages, 7 figures, to match the published version

Journal-ref: JHEP 09 (2025) 072

Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Cosmological stasis is a new type of epoch in the cosmological timeline during which the cosmological abundances of different energy components -- such as vacuum energy, matter, and radiation -- remain constant despite the expansion of the universe. Previous studies have shown that stasis naturally arises in various scenarios beyond the Standard Model, either through sequential decays of states in large towers or via the annihilation of a single particle species in thermal equilibrium with itself. In this work, we demonstrate that stasis can also emerge from the decay of a single particle species whose decay width is dynamically regulated by a scalar field rolling down a Hubble-mass potential. By analyzing the fixed points of the dynamical system, we identify regions of the parameter space where stasis occurs as a global attractor of cosmic evolution. We also find that, depending on the specific abundance configuration, stasis solutions can manifest as either a stable node with asymptotic behavior or a stable spiral exhibiting intrinsic oscillations. Furthermore, we present an explicit model for this realization of stasis and explore its phenomenological constraints and implications.

[36] arXiv:2505.21188 (replaced) [pdf, html, other]

Title: Optimized quantum sensor networks for ultralight dark matter detection

Adriel I. Santoso, Le Bin Ho

Comments: 7 pages, 7 figures

Journal-ref: Physical Review D (Letter) (2025)

Subjects: Quantum Physics (quant-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)

Dark matter (DM) remains one of the most compelling unresolved problems in fundamental physics, motivating the search for new detection approaches. We propose a network-based quantum sensor architecture to enhance sensitivity to ultralight DM fields. Each node in the network is a superconducting qubit, interconnected via controlled-Z gates in symmetric topologies such as line, ring, star, and fully connected graphs. We investigate four- and nine-qubit systems, optimizing both state preparation and measurement using a variational quantum metrology framework. This approach minimizes the quantum and classical Cramér-Rao bounds to identify optimal configurations. Bayesian inference is employed to extract the DM-induced phase shift from measurement outcomes. Our results show that optimized network configurations significantly outperform conventional GHZ-based protocols while maintaining shallow circuit depths compatible with noisy intermediate-scale quantum hardware. Sensitivity remains robust under local dephasing noise. These findings highlight the importance of network structure in quantum sensing and point toward scalable strategies for quantum-enhanced DM detection.

[37] arXiv:2505.23204 (replaced) [pdf, other]

Title: Shadows of naked singularity in Brans-Dicke gravity

Prajwal Hassan Puttasiddappa, Davi C Rodrigues, David F Mota

Comments: Accepted for publication in EPJC. 7 pages, 3 figures. It contains some additional comments and references

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We investigate the observational features of exact vacuum solutions in Brans-Dicke (BD) gravity, focusing on their implications for black hole shadow imaging. Motivated by the Event Horizon Telescope (EHT) observations, we revisit a class of BD solutions that exhibit a naked singularity. These solutions, despite lacking a conventional event horizon, exhibit photon spheres and produce shadow-like features. We analyze null geodesics and perform ray-tracing simulations under a simplified, optically thin accretion disk model to generate synthetic images. Our results show that BD naked singularities can cast shadows smaller than those of Schwarzschild black holes of equivalent mass. We identify the parameter space $-3/2 < \omega < 0$ as physically viable, ensuring attractive gravity and the absence of ghost fields. These findings suggest that BD naked singularities are possible candidates for compact astrophysical objects.

[38] arXiv:2507.02178 (replaced) [pdf, html, other]

Title: Evolution of the Ionizing Photon Luminosity Function

Stephan R. McCandliss, Swara Ravindranath, Sangeeta Malhotra, Chris Packham, Sophia Flury, Alexandra Le Reste, Allison Strom, Marc Postman, John OMeara

Comments: Science Case Development Document for the Habitable Worlds Observatory - 9 pages 6 figures - submitted to ASP conference proceedings 15 September 2025

Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Counting the number and brightness of ionizing radiation sources out to a redshift of z ~ 1.2 will revolutionize our understanding of how the ionizing background is created and sustained by the embedded growth of meta-galactic structures. The sheer number of sparsely separated targets required to efficiently construct redshift binned luminosity functions is industrial in scale, driving the need for low spectral resolution multi-object spectroscopy (MOS) with a short wavelength cut-off ~ 1000 Å, a sensitivity in the far-UV to better than 30 abmag, and an instantaneous field-of-view ~ (2')$^2$. A MOS on Habitable Worlds Observatory is the only instrument that could conceivably carry out such an ambitious observing program. This program will quantify how much of the ionizing radiation produced by galaxies is attenuated by intervening neutral H, He and dust, and how much escapes to maintain the universe in a mostly ionized state.

[39] arXiv:2509.04494 (replaced) [pdf, html, other]

Title: II. Non-Linear Interacting Dark Energy: Analytical Solutions and Theoretical Pathologies

Marcel van der Westhuizen, Amare Abebe, Eleonora Di Valentino

Comments: 38 pages, 19 figures, 12 tables. This work is the second in a series of three companion papers on interacting dark energy: I. Linear Interacting Dark Energy (arXiv:2509.04495), II. Non-Linear Interacting Dark Energy, and III. Summary and Constraints (arXiv:2509.04496)

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We investigate interacting dark energy (IDE) models with phenomenological, non-linear interaction kernels $Q$, specifically $Q_{1}=3H\delta \left(\frac{\rho_{\rm dm}\rho_{\rm de}}{\rho_{\rm dm}+\rho_{\rm de}}\right)$, $Q_{2}=3H\delta \left(\frac{\rho_{\rm dm}^2}{\rho_{\rm dm}+\rho_{\rm de}}\right)$, and $Q_{3}=3H\delta \left(\frac{\rho_{\rm de}^2}{\rho_{\rm dm}+\rho_{\rm de}}\right)$. Using dynamical system techniques developed in our companion paper on linear kernels, we derive new conditions that ensure positive and well-defined energy densities, as well as criteria to avoid future big rip singularities. We find that for $Q_{1}$, all densities remain positive, while for $Q_{2}$ and $Q_{3}$ negative values of either DM or DE are unavoidable if energy flows from DM to DE. We also show that for $Q_{1}$ and $Q_{2}$ a big rip singularity always arises in the phantom regime $w<-1$, whereas for $Q_{3}$ this fate may be avoided if energy flows from DE to DM. In addition, we provide new exact analytical solutions for $\rho_{\rm dm}$ and $\rho_{\rm de}$ in the cases of $Q_{2}$ and $Q_{3}$, and obtain new expressions for the effective equations of state of DM, DE, the total fluid, and the reconstructed dynamical DE equation of state ($w_{\rm dm}^{\rm eff}$, $w_{\rm de}^{\rm eff}$, $w_{\rm tot}^{\rm eff}$, and $\tilde{w}$). Using these results, we discuss phantom crossings, evaluate how each kernel addresses the coincidence problem, and apply statefinder diagnostics to compare the models. These findings extend the theoretical understanding of non-linear IDE models and provide analytical tools for future observational constraints.

[40] arXiv:2509.04495 (replaced) [pdf, html, other]

Title: I. Linear Interacting Dark Energy: Analytical Solutions and Theoretical Pathologies

Marcel van der Westhuizen, Amare Abebe, Eleonora Di Valentino

Comments: 54 pages, 22 figures, 12 tables. This work is the first in a series of three companion papers on interacting dark energy: I. Linear Interacting Dark Energy, II. Non-Linear Interacting Dark Energy (arXiv:2509.04494), and III. Summary and Constraints (arXiv:2509.04496)

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Interacting dark energy (IDE) models, in which dark matter (DM) and dark energy (DE) exchange energy through a non-gravitational interaction, have long been proposed as candidates to address key challenges in modern cosmology. These include the coincidence problem, the $H_0$ and $S_8$ tensions, and, more recently, the hints of dynamical dark energy reported by the DESI collaboration. Given the renewed interest in IDE models, it is crucial to fully understand their parameter space when constraining them observationally, especially with regard to the often-neglected issues of negative energy densities and future big rip singularities. In this work, we present a comparative study of the general linear interaction $Q=3H(\delta_{\rm dm}\rho_{\rm dm} + \delta_{\rm de}\rho_{\rm de})$ and four special cases: $Q=3H\delta(\rho_{\rm dm}+\rho_{\rm de})$, $Q=3H\delta(\rho_{\rm dm}-\rho_{\rm de})$, $Q=3H\delta \rho_{\rm dm}$, and $Q=3H\delta \rho_{\rm de}$. For these five models, we perform a dynamical system analysis and derive new conditions that ensure positive, real, and well-defined energy densities throughout cosmic evolution, as well as criteria to avoid future big rip singularities. We obtain exact analytical solutions for $\rho_{\rm{dm}}$, $\rho_{\rm{de}}$, the effective equations of state ($w_{\mathrm{eff}}^{\rm{dm}}$, $w_{\mathrm{eff}}^{\rm{de}}$, $w_{\mathrm{eff}}^{\rm{tot}}$), and a reconstructed dynamical DE equation of state $\tilde{w}$. Using these results, we examine phantom crossings, address the coincidence problem, and apply the statefinder diagnostic to distinguish between models. We show that energy transfer from DM to DE inevitably produces negative energy densities and make future singularities more likely, while transfer from DE to DM avoids these pathologies and is thus theoretically favored.

[41] arXiv:2509.04496 (replaced) [pdf, html, other]

Title: III. Interacting Dark Energy: Summary of Models, Pathologies, and Constraints

Marcel van der Westhuizen, Amare Abebe, Eleonora Di Valentino

Comments: 17 pages, 1 figure, 4 tables. This work is the third in a series of three companion papers on interacting dark energy: I. Linear Interacting Dark Energy (arXiv:2509.04495), II. Non-Linear Interacting Dark Energy (arXiv:2509.04494), and III. Summary and Constraints

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present an overview of the main results from our two companion papers that are relevant for observational constraints on interacting dark energy (IDE) models. We provide analytical solutions for the dark matter and dark energy densities, $\rho_{\rm dm}$ and $\rho_{\rm de}$, as well as the normalized Hubble function $h(z)$, for eight IDE models. These include five linear IDE models, namely $Q=3H(\delta_{\rm dm} \rho_{\rm dm} + \delta_{\rm de} \rho_{\rm de})$ and four special cases: $Q=3H\delta(\rho_{\rm dm}+\rho_{\rm de})$, $Q=3H\delta(\rho_{\rm dm}-\rho_{\rm de})$, $Q=3H\delta \rho_{\rm dm}$, and $Q=3H\delta \rho_{\rm de}$, together with three non-linear IDE models: $Q=3H\delta \left( \tfrac{\rho_{\rm dm} \rho_{\rm de}}{\rho_{\rm dm}+\rho_{\rm de}} \right)$, $Q=3H\delta \left( \tfrac{\rho_{\rm dm}^2}{\rho_{\rm dm}+\rho_{\rm de}} \right)$, and $Q=3H\delta \left( \tfrac{\rho_{\rm de}^2}{\rho_{\rm dm}+\rho_{\rm de}} \right)$. For these eight models, we present conditions to avoid imaginary, undefined, and negative energy densities. In seven of the eight cases, negative densities arise if energy flows from DM to DE, implying a strong theoretical preference for energy transfer from DE to DM. We also provide conditions to avoid future big rip singularities and evaluate how each model addresses the coincidence problem in both the past and the future. Finally, we propose a set of approaches and simplifying assumptions that can be used when constraining IDE models, by defining regimes that restrict the parameter space according to the behavior researchers are willing to tolerate.