Hanyu Cheng, Eleonora Di Valentino, Luis A. Escamilla, Anjan A. Sen and Luca Visinelli
{"title":"Pressure parametrization of dark energy: first and second-order constraints with latest cosmological data","authors":"Hanyu Cheng, Eleonora Di Valentino, Luis A. Escamilla, Anjan A. Sen and Luca Visinelli","doi":"10.1088/1475-7516/2025/09/031","DOIUrl":"https://doi.org/10.1088/1475-7516/2025/09/031","url":null,"abstract":"We explore an extension of the ΛCDM model in which the pressure p of the dark energy (DE) fluid evolves with the expansion of the Universe, expressed as a function of the scale factor a. The corresponding energy density ρ is derived from the continuity equation, resulting in a dynamical equation-of-state parameter w ≡ p/ρ during the late-time expansion of the Universe. The pressure is modeled using a Taylor expansion around the present epoch (a = 1), introducing deviations from a cosmological constant within the dynamical dark energy (DDE) framework. At first order, a single new parameter Ω1 captures linear deviations, while a second-order parameter, Ω2, accounts for quadratic evolution in the pressure. We constrain the first- and second-order DDE models using multiple observational datasets and compare their performance against ΛCDM and the CPL parameterization. A joint analysis of Planck CMB, DESI, and DESY5 data yields the strongest evidence for DDE, with a 2.7σ deviation in the first-order model and over 4σ in the second-order model — providing strong statistical support for a departure from a cosmological constant. The reconstructed DE evolution in the second-order case reveals a distinctive non-monotonic behavior in both energy density and wDE(a), including clear phantom-crossing phenomena. Notably, the late-time evolution of wDE(a) remains consistent across datasets and shows strong agreement with the CPL parameterization, underscoring the robustness of the pressure-based approach.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"16 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145035464","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kalliopi Petraki, Anna Socha and Christiana Vasilaki
{"title":"The role of unitarisation on dark-matter freeze-out via metastable bound states","authors":"Kalliopi Petraki, Anna Socha and Christiana Vasilaki","doi":"10.1088/1475-7516/2025/09/026","DOIUrl":"https://doi.org/10.1088/1475-7516/2025/09/026","url":null,"abstract":"In many Abelian and non-Abelian theories, standard calculations of radiative bound-state formation violate partial-wave unitarity — even at arbitrarily small couplings — when capture into excited states is considered. Recent work demonstrated that unitarity can be restored by the proper resummation of squared inelastic processes in the self-energy of the incoming state. We examine how unitarisation affects dark-matter thermal decoupling, given that the formation and decay of metastable dark-matter bound states are critical in determining the relic abundance, especially for multi-TeV dark matter. We consider an Abelian model featuring bound-state formation via emission of a light scalar that carries a conserved charge, whose dynamics also emulates relevant aspects of non-Abelian theories. Incorporating capture into excited states, we show that, without proper treatment, unitarity violation is so severe as to prevent freeze-out. Resumming the squared bound-state formation processes restores unitarity and ensures freeze-out, while capture into excited levels still significantly depletes dark matter. We further discuss the impact of higher partial waves, both within and beyond the present model. Finally, we point out the intriguing possibility of late dark-matter decoupling that can affect structure formation.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"2 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145025340","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Spontaneous magnetogenesis at the electroweak phase transition","authors":"Valerie Domcke, Yohei Ema and Teerthal Patel","doi":"10.1088/1475-7516/2025/09/023","DOIUrl":"https://doi.org/10.1088/1475-7516/2025/09/023","url":null,"abstract":"Spontaneous CP violation during the electroweak phase transition can induce a twisting of the magnetic field configuration of Standard Model dumbbells, resulting in sizable intergalactic magnetic fields and a small baryon asymmetry, in agreement with observations. We demonstrate this by coupling the electroweak gauge group of the Standard Model to an axion-like particle with a non-vanishing velocity. Studying the resulting monopole, string and dumbbell configurations, we conclude that the helicity fraction of the magnetic fields generated at the electroweak phase transition is roughly given by the dimensionless axion velocity.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"63 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145025337","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Precision calculation of the EFT likelihood with primordial non-Gaussianities","authors":"Ji-Yuan Ke, Yun Wang and Ping He","doi":"10.1088/1475-7516/2025/09/029","DOIUrl":"https://doi.org/10.1088/1475-7516/2025/09/029","url":null,"abstract":"We perform a precision calculation of the effective field theory (EFT) conditional likelihood for large-scale structure (LSS) using the saddle-point expansion method in the presence of primordial non-Gaussianities (PNG). The precision is manifested at two levels: one corresponding to the consideration of higher-order noise terms, and the other to the inclusion of contributions from the saddle-point fluctuations. When computing the latter, we encounter the same issue of the negative modes as in the context of false vacuum decay, which necessitates deforming the original integration contour into a combination of the steepest descent contours to ensure a convergent and real result. We demonstrate through detailed calculations that, upon incorporating leading-order PNG, both types of extensions introduce irreducible field-dependent contributions to the conditional likelihood. This insight motivates the systematic inclusion of additional effective terms within the forward modeling framework. Our work facilitates Bayesian forward modeling under non-Gaussian initial conditions, thereby enabling more stringent constraints on the parameters describing PNG.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"57 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145025405","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sayantan Ghosh, Tianqi Zhao, Bharat Kumar and Sailesh Ranjan Mohanty
{"title":"The role of adiabatic sound speeds in neutron star radial oscillations and stability","authors":"Sayantan Ghosh, Tianqi Zhao, Bharat Kumar and Sailesh Ranjan Mohanty","doi":"10.1088/1475-7516/2025/09/025","DOIUrl":"https://doi.org/10.1088/1475-7516/2025/09/025","url":null,"abstract":"We investigate the impact of adiabatic sound speed on the radial oscillations and stability of neutron stars (NSs), using five representative equations of state (EOSs): three hadronic (FSU2R, HPUC, SINPA) and two hybrid (Gibbs 40, KW 55). The adiabatic case, which assumes fixed particle composition during compression, corresponds to slow reaction scenarios and leads to an extension of the stable branch toward smaller radii and higher compactness, even beyond the maximum mass configuration. This extended regime, known as the “slow stable” branch, remains dynamically stable only when reactions are sufficiently slow. To assess stability, we subject the NSs to radial perturbations and examine their fundamental radial (f-mode) oscillations, identifying the transition point where the mode frequency vanishes. The adiabatic sound speed, compared to the equilibrium sound speed, delays the onset of instability, allowing NSs to sustain stability at higher compactness and thus exhibit smaller radii — a more physically realistic outcome for slow reaction rates. Notably, the delays in the onset of instability are more pronounced for hybrid EOSs than for hadronic ones.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"18 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145025339","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Entropy production at electroweak bubble walls from scalar field fluctuations","authors":"M. Eriksson and M. Laine","doi":"10.1088/1475-7516/2025/09/027","DOIUrl":"https://doi.org/10.1088/1475-7516/2025/09/027","url":null,"abstract":"The real-time dynamics of an electroweak phase transition involves large time and distance scales, the domain of hydrodynamics. However, the matching conditions of ideal hydrodynamics across a bubble wall do not fix the fluid profile completely, with the remaining degree of freedom parametrizable through entropy production. Within a framework of Langevin dynamics, viewed as an effective description valid between the hydrodynamic (k ∼ g4T/n3) and soft momentum scales (k ∼ gT), we determine the entropy production originating from scalar field fluctuations. The entropy discontinuity is shown to remain non-vanishing when the friction coefficient is sent to zero, in apparent violation of the “local thermal equilibrium” (LTE) framework. To confirm the finding, we identify its origin within Boltzmann equations, as being part of the 1 → 1 force associated with the “ballistic” regime. The result implies that LTE-based upper bounds on the wall velocity cannot be saturated.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"103 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145025341","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Quasi-Palatini formulation of scalar-tensor gravity","authors":"Sotirios Karamitsos","doi":"10.1088/1475-7516/2025/09/022","DOIUrl":"https://doi.org/10.1088/1475-7516/2025/09/022","url":null,"abstract":"The Palatini formulation has been successful in the development of several alternative theories of gravity. It is well understood that the Palatini and metric formulations are equivalent in minimally coupled scalar-tensor models, but nonminimal scalar-tensor models can lead to physically distinct theories depending on the underlying formulation. Once a model has been selected, the choice of formulation is a discrete one, and so promoting it to be continuous is expected to give rise to a wider class of actions. To this end, we propose the “quasi-Palatini” formulation, a method for interpolating between the metric and Palatini formulations for a given model that gives rise to a continuous family of models. We apply the quasi-Palatini formulation to Higgs inflation, induced gravity inflation, and Starobinsky inflation, and demonstrate how this leads to a deformation of the potential with a tangible effect on the observables. We also discuss how the interpolation between different actions can be extended to scalar-torsion and scalar-nonmetricity models.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"44 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145025336","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Francisco S.N. Lobo, Jorde A.A. Ramos and Manuel E. Rodrigues
{"title":"Supermassive black hole in NGC 4649 (M60) with a dark matter halo: impact on shadow measurements and thermodynamic properties","authors":"Francisco S.N. Lobo, Jorde A.A. Ramos and Manuel E. Rodrigues","doi":"10.1088/1475-7516/2025/09/024","DOIUrl":"https://doi.org/10.1088/1475-7516/2025/09/024","url":null,"abstract":"We investigate black hole (BH) solutions embedded in a dark matter (DM) halo, modeled as extensions of the Schwarzschild metric. The DM density profile is constrained by Hubble Space Telescope (HST) data, stellar dynamics, and globular cluster (GC) measurements of the elliptical galaxy NGC 4649 (M60). Using this profile, we construct two distinct spacetime solutions characterized by the black hole mass (M), critical velocity (Vc), and core radius (a), all reducing to the Schwarzschild case in the limit Vc = 0 and a = 0. Our results show that the DM halo modifies essential BH features, such as the event horizon radius and spacetime curvature, as reflected in the Kretschmann scalar. We also derive an approximate analytical expression for the BH shadow radius, which increases slightly due to the halo's influence. Comparisons with two observational datasets further validate the analysis. Thermodynamic properties are examined across the two models. In the first, a generalized Smarr formula is obtained via two additional variables, γ and a. The second incorporates halo effects through Vc and a. These results underscore the role of DM in shaping both geometric and thermodynamic aspects of BHs.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"67 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145025338","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mathew Thomas Arun, Prachiti P. Athalye and Basabendu Barman
{"title":"Light PIDM in warped extra dimensions","authors":"Mathew Thomas Arun, Prachiti P. Athalye and Basabendu Barman","doi":"10.1088/1475-7516/2025/09/028","DOIUrl":"https://doi.org/10.1088/1475-7516/2025/09/028","url":null,"abstract":"Traditional Planckian Interacting Dark Matter (PIDM), which interacts exclusively through gravity, typically requires heavy DM candidates (with mass 103–1015 GeV) and very high reheating temperature (Trh ≳ 1015 GeV). In this article, we explore a novel realization of PIDM in warped five-dimensions, consisting of an Ultra Violet-Dark-Infra Red (UV-DB-IR) brane setup, where the DM can be a Dark brane composite light state with mass 1 MeV–1 TeV. The DM sector is assumed to interact solely via gravity in five-dimensions. After orbifolding and performing a Kaluza-Klein (KK) decomposition, the DM is assumed to be localized onto the DB, which is positioned in the extra-dimension such that the DM interacts with both the massless graviton and its massive KK excitations, with suppressed couplings to remain consistent with the ethos of the PIDM framework. The light (heavy) Standard Model matter is assumed to be localized near UV (IR) branes for the geometric Froggatt-Neilsen mechanism, while their KK modes are localized close to the IR brane. We show that this construction allows for a viable and efficient freeze-in production mechanism for light composite PIDM, consistent with TeV-scale reheating temperature.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"13 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145025404","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Michele Lenzi, Arnau Montava Agudo and Carlos F. Sopuerta
{"title":"Korteweg-de Vries integrals for modified black hole potentials: instabilities and other questions","authors":"Michele Lenzi, Arnau Montava Agudo and Carlos F. Sopuerta","doi":"10.1088/1475-7516/2025/09/021","DOIUrl":"https://doi.org/10.1088/1475-7516/2025/09/021","url":null,"abstract":"Quasi-normal modes (QNMs) and greybody factors are some of the most characteristic features of the dynamics of black holes (BHs) and represent the basis for a number of fundamental physics tests with gravitational wave observations. It is therefore important to understand the properties of these quantities, naturally introduced within BH perturbation theory, in particular the stability properties under modifications of the BH potential. Instabilities in the QNMs have been recently shown to appear in the BH pseudospectrum under certain circumstances. In this work, we give a novel point of view based on the existence of some recently discovered hidden symmetries in BH dynamics and the associated infinite series of conserved quantities, the Korteweg-de Vries (KdV) integrals. We provide different motivations to use the KdV integrals as indicators of some crucial BH spectral properties. In particular, by studying them in different scenarios described by modified BH barriers, we find strong evidence that the KdV conserved quantities represent a useful tool to look for instabilities in the BH spectrum of QNMs and in their greybody factors.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"14 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2025-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144995704","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}