Pub Date : 2026-01-05DOI: 10.1088/1475-7516/2026/01/016
Mustafa A. Amin, M. Sten Delos and Mehrdad Mirbabayi
We investigate the evolution of density perturbations in dark matter, including the new combined effects of finite number density and non-zero velocity dispersion. Using a truncated BBGKY hierarchy, we derive analytical expressions for the dark matter power spectrum during radiation and matter domination. A component of warm white noise emerges in our analysis, which arises due to the finite number density and undergoes scale-dependent evolution because of the velocity dispersion. Although free streaming erases adiabatic initial perturbations on small scales, warm white noise persists below the free-streaming length and grows during matter domination, with growth suppressed below the dark matter Jeans length. Our calculated power spectra agree with N-body simulations in the linear regime and accurately predict halo mass functions in the nonlinear regime. Effects of warm white noise can emerge on observable quasi-linear scales for ultralight dark matter produced after inflation with a subhorizon correlation length. Our formalism is applicable to these scenarios (with de Broglie-scale quasi-particles), to cases in which dark matter includes macroscopic structures (such as primordial black holes), and to traditional warm and cold dark matter scenarios.
{"title":"Structure formation with warm white noise: Effects of finite number density and velocity dispersion in particle and wave dark matter","authors":"Mustafa A. Amin, M. Sten Delos and Mehrdad Mirbabayi","doi":"10.1088/1475-7516/2026/01/016","DOIUrl":"https://doi.org/10.1088/1475-7516/2026/01/016","url":null,"abstract":"We investigate the evolution of density perturbations in dark matter, including the new combined effects of finite number density and non-zero velocity dispersion. Using a truncated BBGKY hierarchy, we derive analytical expressions for the dark matter power spectrum during radiation and matter domination. A component of warm white noise emerges in our analysis, which arises due to the finite number density and undergoes scale-dependent evolution because of the velocity dispersion. Although free streaming erases adiabatic initial perturbations on small scales, warm white noise persists below the free-streaming length and grows during matter domination, with growth suppressed below the dark matter Jeans length. Our calculated power spectra agree with N-body simulations in the linear regime and accurately predict halo mass functions in the nonlinear regime. Effects of warm white noise can emerge on observable quasi-linear scales for ultralight dark matter produced after inflation with a subhorizon correlation length. Our formalism is applicable to these scenarios (with de Broglie-scale quasi-particles), to cases in which dark matter includes macroscopic structures (such as primordial black holes), and to traditional warm and cold dark matter scenarios.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"38 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145897755","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}
Pub Date : 2026-01-05DOI: 10.1088/1475-7516/2026/01/006
S.K. Maurya, A. Errehymy, Ksh. Newton Singh, G. Mustafa and Saibal Ray
The merger of binary neutron stars (BNSs) is a remarkable astrophysical event where all four fundamental forces interplay dynamically across multiple stages, producing a rich spectrum of multi-messenger signals. These observations present a significant multiphysics modeling challenge but also offer a unique opportunity to probe the nature of gravity and the strong nuclear interaction under extreme conditions. The landmark detection of GW170817 provided essential constraints on the properties of non-rotating neutron stars (NSs), including their maximum mass (Mmax) and radius distribution, thereby informing the equation of state (EOS) of cold, dense nuclear matter. While the inspiral phase of such events has been extensively studied, the post-merger signal holds even greater potential to reveal the behavior of matter at supranuclear densities, particularly in scenarios involving a transition to deconfined quark matter. Motivated by the recent gravitational wave event GW190814 (2.5–2.67 M⊙), we revisit the modeling of high-mass compact stars to investigate their internal structure via a generalized polytropic EOS. This framework incorporates a modified energy density profile and is coupled with the Tolman-Oppenheimer-Volkoff (TOV) equations. We explore mass-radius (M–R) relationships within both general relativity (GR) and the minimal geometric deformation (MGD) approach. Specifically, we constrain the radii of four massive compact objects — PSR J1614–2230 (1.97+0.04-0.04M⊙), PSR J0952–0607 (2.35+0.17-0.17M⊙), GW190814 (2.5–2.67 M⊙), and GW200210 (2.83+0.47-0.42M⊙) — and demonstrate that our theoretical M–R curves are consistent with observational data. These findings provide meaningful constraints on the EOS and underscore the potential of alternative gravity models to accommodate ultra-massive compact stars within a physically consistent framework.
{"title":"Relativistic massive compact stars supported by decoupled matter: implications for mass-radius bounds","authors":"S.K. Maurya, A. Errehymy, Ksh. Newton Singh, G. Mustafa and Saibal Ray","doi":"10.1088/1475-7516/2026/01/006","DOIUrl":"https://doi.org/10.1088/1475-7516/2026/01/006","url":null,"abstract":"The merger of binary neutron stars (BNSs) is a remarkable astrophysical event where all four fundamental forces interplay dynamically across multiple stages, producing a rich spectrum of multi-messenger signals. These observations present a significant multiphysics modeling challenge but also offer a unique opportunity to probe the nature of gravity and the strong nuclear interaction under extreme conditions. The landmark detection of GW170817 provided essential constraints on the properties of non-rotating neutron stars (NSs), including their maximum mass (Mmax) and radius distribution, thereby informing the equation of state (EOS) of cold, dense nuclear matter. While the inspiral phase of such events has been extensively studied, the post-merger signal holds even greater potential to reveal the behavior of matter at supranuclear densities, particularly in scenarios involving a transition to deconfined quark matter. Motivated by the recent gravitational wave event GW190814 (2.5–2.67 M⊙), we revisit the modeling of high-mass compact stars to investigate their internal structure via a generalized polytropic EOS. This framework incorporates a modified energy density profile and is coupled with the Tolman-Oppenheimer-Volkoff (TOV) equations. We explore mass-radius (M–R) relationships within both general relativity (GR) and the minimal geometric deformation (MGD) approach. Specifically, we constrain the radii of four massive compact objects — PSR J1614–2230 (1.97+0.04-0.04M⊙), PSR J0952–0607 (2.35+0.17-0.17M⊙), GW190814 (2.5–2.67 M⊙), and GW200210 (2.83+0.47-0.42M⊙) — and demonstrate that our theoretical M–R curves are consistent with observational data. These findings provide meaningful constraints on the EOS and underscore the potential of alternative gravity models to accommodate ultra-massive compact stars within a physically consistent framework.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"57 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145897700","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}
Pub Date : 2026-01-05DOI: 10.1088/1475-7516/2026/01/010
Aryabrat Mahapatra, Adarsh Pandey, Debojyoti Garain and Tapobrata Sarkar
We present the results of a suite of numerical simulations using smoothed particle hydrodynamics to study partial tidal disruption events (TDEs) of white dwarfs (WDs) in off-equatorial orbits in intermediate mass spinning (Kerr) black hole backgrounds. We carry out this analysis for both parabolic and eccentric WD orbits and also take into account possible initial WD spins. Our objective here is to quantify the differences in variables like the mass of the self-bound core, the peak fallback rate of debris and gravitational wave signature in off-equatorial orbits compared to equatorial ones. The analysis is carried out using a hybrid numerical scheme, one which involves integrating the exact Kerr geodesics while adopting a Newtonian formalism for the stellar fluid dynamics, justified by our choice of simulation parameters. We find that the physics of TDEs in off-equatorial orbits present several interesting and novel features due to black hole spin, which in some cases enhances when coupled with the rotation of the WD. However, numerical values of observable quantities in TDEs involving off-equatorial orbits cannot possibly distinguish between such orbits from equatorial ones. We further comment on the genericness of our results and argue that these should extend to a general TDE scenario involving a spinning BH.
{"title":"Partial tidal disruption of white dwarfs in off-equatorial orbits around Kerr black holes","authors":"Aryabrat Mahapatra, Adarsh Pandey, Debojyoti Garain and Tapobrata Sarkar","doi":"10.1088/1475-7516/2026/01/010","DOIUrl":"https://doi.org/10.1088/1475-7516/2026/01/010","url":null,"abstract":"We present the results of a suite of numerical simulations using smoothed particle hydrodynamics to study partial tidal disruption events (TDEs) of white dwarfs (WDs) in off-equatorial orbits in intermediate mass spinning (Kerr) black hole backgrounds. We carry out this analysis for both parabolic and eccentric WD orbits and also take into account possible initial WD spins. Our objective here is to quantify the differences in variables like the mass of the self-bound core, the peak fallback rate of debris and gravitational wave signature in off-equatorial orbits compared to equatorial ones. The analysis is carried out using a hybrid numerical scheme, one which involves integrating the exact Kerr geodesics while adopting a Newtonian formalism for the stellar fluid dynamics, justified by our choice of simulation parameters. We find that the physics of TDEs in off-equatorial orbits present several interesting and novel features due to black hole spin, which in some cases enhances when coupled with the rotation of the WD. However, numerical values of observable quantities in TDEs involving off-equatorial orbits cannot possibly distinguish between such orbits from equatorial ones. We further comment on the genericness of our results and argue that these should extend to a general TDE scenario involving a spinning BH.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"21 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145897704","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}
Pub Date : 2026-01-05DOI: 10.1088/1475-7516/2026/01/019
Rahima Mokeddem, Bruno B. Bizarria, Jiajun Zhang, Wiliam S. Hipólito-Ricaldi, Carlos Alexandre Wuensche, Elcio Abdalla, Filipe B. Abdalla, Amilcar R. Queiroz, Thyrso Villela, Bin Wang, Chang Feng, Edmar C. Gurjão and Alessandro Marins
We present a novel application of cosmological rescaling, or “remapping”, to generate 21 cm intensity mapping mocks for different cosmologies. The remapping method allows for computationally efficient generation of N-body catalogs by rescaling existing simulations. In this work, we employ the remapping method to construct dark matter halo catalogs, starting from the Horizon Run 4 simulation with WMAP5 cosmology, and apply it to different target cosmologies, including WMAP7, Planck18 and Chevallier-Polarski-Linder (CPL) models. These catalogs are then used to simulate 21 cm intensity maps. We use the halo occupation distribution (HOD) method to populate halos with neutral hydrogen (HI) and derive 21 cm brightness temperature maps. Our results demonstrate the effectiveness of the remapping approach in generating cosmological simulations for large-scale structure studies, offering an alternative for testing observational data pipelines and performing cosmological parameter forecasts without the need for computationally expensive full N-body simulations. We also analyze the precision and limitations of the remapping, in light of the rescaling parameters s and sm, as well as the effects of the halo mass and box size thresholds.
我们提出了一种新的宇宙学重新缩放或“重新映射”的应用，以生成不同宇宙学的21厘米强度映射模型。重新映射方法允许通过重新缩放现有模拟来计算高效地生成n体目录。本文从WMAP5宇宙学的Horizon Run 4模拟开始，采用重映射方法构建暗物质晕星表，并将其应用于WMAP7、Planck18和Chevallier-Polarski-Linder （CPL）模型等不同的目标宇宙学。然后用这些目录来模拟21厘米的强度图。我们利用光晕占位分布（HOD）方法用中性氢（HI）填充光晕，得到了21 cm的亮度温度图。我们的研究结果证明了重映射方法在为大规模结构研究生成宇宙学模拟方面的有效性，为测试观测数据管道和执行宇宙学参数预测提供了一种替代方法，而不需要计算昂贵的全n体模拟。我们还分析了重新映射的精度和局限性，根据重新缩放参数s和sm，以及光晕质量和盒尺寸阈值的影响。
{"title":"Cosmological remapping for efficient generation of 21 cm intensity mapping mocks","authors":"Rahima Mokeddem, Bruno B. Bizarria, Jiajun Zhang, Wiliam S. Hipólito-Ricaldi, Carlos Alexandre Wuensche, Elcio Abdalla, Filipe B. Abdalla, Amilcar R. Queiroz, Thyrso Villela, Bin Wang, Chang Feng, Edmar C. Gurjão and Alessandro Marins","doi":"10.1088/1475-7516/2026/01/019","DOIUrl":"https://doi.org/10.1088/1475-7516/2026/01/019","url":null,"abstract":"We present a novel application of cosmological rescaling, or “remapping”, to generate 21 cm intensity mapping mocks for different cosmologies. The remapping method allows for computationally efficient generation of N-body catalogs by rescaling existing simulations. In this work, we employ the remapping method to construct dark matter halo catalogs, starting from the Horizon Run 4 simulation with WMAP5 cosmology, and apply it to different target cosmologies, including WMAP7, Planck18 and Chevallier-Polarski-Linder (CPL) models. These catalogs are then used to simulate 21 cm intensity maps. We use the halo occupation distribution (HOD) method to populate halos with neutral hydrogen (HI) and derive 21 cm brightness temperature maps. Our results demonstrate the effectiveness of the remapping approach in generating cosmological simulations for large-scale structure studies, offering an alternative for testing observational data pipelines and performing cosmological parameter forecasts without the need for computationally expensive full N-body simulations. We also analyze the precision and limitations of the remapping, in light of the rescaling parameters s and sm, as well as the effects of the halo mass and box size thresholds.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"1 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145897732","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}
Pub Date : 2026-01-05DOI: 10.1088/1475-7516/2026/01/003
Jose A.R. Cembranos, Luis J. Garay, Álvaro Parra-López and Javier Ortega del Río
Gravitational production of scalar, non-minimally coupled dark matter depends on the specifics of the inflationary model under consideration. We analyze both Starobinsky inflation and a quadratic potential, solve the full background dynamics, study pair production during inflation and reheating, and find that the observed dark matter abundance can be explained solely by this mechanism, regardless of the inflationary model. Qualitative differences between the two cases only appear for dark matter masses close to the inflationary scale. In addition, we identify a large region in parameter space in which gravitational production of dark matter is mostly independent of the chosen inflationary potential, highlighting the robustness of this dark matter production mechanism and its independence of the unknown particular details of inflation. In the region of masses lower than the scale of inflation, and sufficiently away from the conformal limit, the total comoving number density of produced particles becomes a function of the coupling to the geometry alone. This allows us to provide an approximated analytic expression for fitting the resulting abundance.
{"title":"Estimation of gravitational production uncertainties","authors":"Jose A.R. Cembranos, Luis J. Garay, Álvaro Parra-López and Javier Ortega del Río","doi":"10.1088/1475-7516/2026/01/003","DOIUrl":"https://doi.org/10.1088/1475-7516/2026/01/003","url":null,"abstract":"Gravitational production of scalar, non-minimally coupled dark matter depends on the specifics of the inflationary model under consideration. We analyze both Starobinsky inflation and a quadratic potential, solve the full background dynamics, study pair production during inflation and reheating, and find that the observed dark matter abundance can be explained solely by this mechanism, regardless of the inflationary model. Qualitative differences between the two cases only appear for dark matter masses close to the inflationary scale. In addition, we identify a large region in parameter space in which gravitational production of dark matter is mostly independent of the chosen inflationary potential, highlighting the robustness of this dark matter production mechanism and its independence of the unknown particular details of inflation. In the region of masses lower than the scale of inflation, and sufficiently away from the conformal limit, the total comoving number density of produced particles becomes a function of the coupling to the geometry alone. This allows us to provide an approximated analytic expression for fitting the resulting abundance.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"38 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145897696","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}
Pub Date : 2026-01-05DOI: 10.1088/1475-7516/2026/01/009
Yi-Ying Wang, Lei Lei, Shao-Peng Tang and Yi-Zhong Fan
Cosmological measurements have revealed tensions within the standard ΛCDM model, notably discrepancies in the Hubble constant and S8 parameter. A modified recombination scenario involving a time-varying electron mass has been proposed as a feasible solution to the Hubble tension without exacerbating the S8 tension. Recent observations have further revealed other potential deviations from the ΛCDM framework, such as non-flat spatial curvature and an anomalous CMB lensing amplitude. In this study, we explore whether introducing a variation in the electron mass me, allowing non-zero spatial curvature ΩK, and a free lensing amplitude Alens can resolve these persistent tensions. Using the Planck Public Release (PR) 3 and ACT power spectra, Planck PR4 and ACT lensing maps, together with BAO measurements from DESI DR2, we obtain H0 = 69.61+0.60-0.55 km s-1 Mpc-1 and S8 = 0.808±0.012, with Δme/me = 0.0109+0.0068-0.0066 and Alens = 1.030+0.039-0.037, both exceeding the ΛCDM expectations. We find no indication of spatial curvature deviating from flatness, even when including the Cosmic Chronometers and SNe Ia samples. However, when adopting the latest Planck power spectra likelihoods, NPIPE and HiLLiPoP, we obtain lower electron masses with Δme/me = -0.0063+0.0095-0.0099 and -0.0095+0.0078-0.0079, relieving the S8 tension only. The lensing amplitude remains anomalously high, with Alens = 1.053+0.042-0.040 and 1.075+0.044-0.043. Our results point to a promising direction for cosmological models to reconcile the aforementioned discrepancies, although more precise data from future experiments will be necessary to clarify the aforementioned modifications.
{"title":"Lensing amplitude anomaly and varying electron mass alleviate the Hubble and S 8 tensions","authors":"Yi-Ying Wang, Lei Lei, Shao-Peng Tang and Yi-Zhong Fan","doi":"10.1088/1475-7516/2026/01/009","DOIUrl":"https://doi.org/10.1088/1475-7516/2026/01/009","url":null,"abstract":"Cosmological measurements have revealed tensions within the standard ΛCDM model, notably discrepancies in the Hubble constant and S8 parameter. A modified recombination scenario involving a time-varying electron mass has been proposed as a feasible solution to the Hubble tension without exacerbating the S8 tension. Recent observations have further revealed other potential deviations from the ΛCDM framework, such as non-flat spatial curvature and an anomalous CMB lensing amplitude. In this study, we explore whether introducing a variation in the electron mass me, allowing non-zero spatial curvature ΩK, and a free lensing amplitude Alens can resolve these persistent tensions. Using the Planck Public Release (PR) 3 and ACT power spectra, Planck PR4 and ACT lensing maps, together with BAO measurements from DESI DR2, we obtain H0 = 69.61+0.60-0.55 km s-1 Mpc-1 and S8 = 0.808±0.012, with Δme/me = 0.0109+0.0068-0.0066 and Alens = 1.030+0.039-0.037, both exceeding the ΛCDM expectations. We find no indication of spatial curvature deviating from flatness, even when including the Cosmic Chronometers and SNe Ia samples. However, when adopting the latest Planck power spectra likelihoods, NPIPE and HiLLiPoP, we obtain lower electron masses with Δme/me = -0.0063+0.0095-0.0099 and -0.0095+0.0078-0.0079, relieving the S8 tension only. The lensing amplitude remains anomalously high, with Alens = 1.053+0.042-0.040 and 1.075+0.044-0.043. Our results point to a promising direction for cosmological models to reconcile the aforementioned discrepancies, although more precise data from future experiments will be necessary to clarify the aforementioned modifications.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"14 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145897702","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}
Pub Date : 2026-01-05DOI: 10.1088/1475-7516/2026/01/017
Swarnim Shirke, Bikram Keshari Pradhan, Debarati Chatterjee, Laura Sagunski and Jürgen Schaffner-Bielich
Boson Stars are macroscopic self-gravitating configurations made of complex scalar fields. These exotic compact objects would manifest as dark Boson stars and, in the absence of electromagnetic signatures, could mimic properties of compact stars in the gravitational wave spectrum. In a recent study, using the simplest potential for massive Boson stars, we demonstrated that fundamental non-radial oscillations (f-modes) obey scaling relations that allow them to be distinguished from neutron stars and black holes. In this work, we provide analytical fits for these scaling relations, valid for the dark matter parameter space compatible with current astrophysical and cosmological data, that can be directly incorporated into future studies of massive Boson stars in the strong coupling regime, avoiding the need for numerical calculations. We also provide analytical fits for empirical and universal relations for gravitational wave asteroseismology, which can be used to infer microscopic dark matter properties following a successful detection. Further, we investigate the possibility of detection of f-modes and the dark matter parameter space that can be probed with current and future gravitational wave detectors across multiple frequency bands. Assuming a burst GW model and demanding a signal-to-noise ratio of 5, we show that the current and future detectors can, in principle, probe Boson star f-modes up to cosmological distances: 1 Mpc with aLIGO, 30 Mpc with Cosmic Explorer and Einstein Telescope, and in the best case scenario, about 300 Mpc with LISA.
{"title":"Detectability of massive boson stars using gravitational waves from fundamental oscillations","authors":"Swarnim Shirke, Bikram Keshari Pradhan, Debarati Chatterjee, Laura Sagunski and Jürgen Schaffner-Bielich","doi":"10.1088/1475-7516/2026/01/017","DOIUrl":"https://doi.org/10.1088/1475-7516/2026/01/017","url":null,"abstract":"Boson Stars are macroscopic self-gravitating configurations made of complex scalar fields. These exotic compact objects would manifest as dark Boson stars and, in the absence of electromagnetic signatures, could mimic properties of compact stars in the gravitational wave spectrum. In a recent study, using the simplest potential for massive Boson stars, we demonstrated that fundamental non-radial oscillations (f-modes) obey scaling relations that allow them to be distinguished from neutron stars and black holes. In this work, we provide analytical fits for these scaling relations, valid for the dark matter parameter space compatible with current astrophysical and cosmological data, that can be directly incorporated into future studies of massive Boson stars in the strong coupling regime, avoiding the need for numerical calculations. We also provide analytical fits for empirical and universal relations for gravitational wave asteroseismology, which can be used to infer microscopic dark matter properties following a successful detection. Further, we investigate the possibility of detection of f-modes and the dark matter parameter space that can be probed with current and future gravitational wave detectors across multiple frequency bands. Assuming a burst GW model and demanding a signal-to-noise ratio of 5, we show that the current and future detectors can, in principle, probe Boson star f-modes up to cosmological distances: 1 Mpc with aLIGO, 30 Mpc with Cosmic Explorer and Einstein Telescope, and in the best case scenario, about 300 Mpc with LISA.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"79 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145897726","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}
Pub Date : 2026-01-05DOI: 10.1088/1475-7516/2026/01/014
Raphaël Kou and Antony Lewis
Recent BAO measurements from DESI, when combined with CMB and supernovae data, suggest evolving dark energy and in particular point to a possible phantom regime, with an equation of state parameter w < -1. This behaviour is theoretically problematic, as it violates the null energy condition and typically leads to instabilities in the perturbations. We explore an alternative phenomenological way to model dark matter and dark energy based on a unified dark fluid (UDF). By construction, our model reproduces the same background expansion history as DESI's best-fit using the Chevallier–Polarski–Linder (CPL) parametrization, but assumes a vanishing rest-frame sound speed and no anisotropic stress. This simple prescription ensures a consistent and physical treatment of perturbations and, in our case, the use of a unified dark sector avoids phantom behaviour. We model CMB, large-scale structure, and redshift-space distortion observables, and find mostly small differences with CPL, suggesting that while stage IV CMB and galaxy surveys will be able to test these models, achieving a decisive distinction between them may prove challenging on linear scales. At the non-linear level, we study spherical collapse in the UDF and show that within this framework, structure formation proceeds very similarly to standard scenarios. Using Planck, DESI BAO DR2, and DES Y5 supernovae data, we demonstrate that this simple UDF model fits current observations nearly as well as CPL, while treating perturbations consistently. Because most cosmological observations are not sensitive to how the dark sector is split, the unified framework can also approximate the phenomenology of interacting dark energy–dark matter scenarios or evolving dark matter, making it a general way to model the data, at least as long as the dark components have a vanishing sound speed, which is the most distinctive feature of our analysis. Our results highlight that a unified dark fluid with evolving equation of state and null sound speed is sufficient to pass current constraints without invoking a phantom component.
最近来自DESI的BAO测量，当与CMB和超新星数据相结合时，表明暗能量的演变，特别是指向一个可能的幽灵状态，其状态参数方程为w < -1。这种行为在理论上是有问题的，因为它违反了零能量条件，并且通常会导致扰动中的不稳定。我们探索了一种基于统一暗流体（UDF）的替代现象学方法来模拟暗物质和暗能量。通过构造，我们的模型使用Chevallier-Polarski-Linder （CPL）参数化再现了与DESI最佳拟合相同的背景膨胀历史，但假设静止帧声速消失并且没有各向异性应力。这个简单的处方确保了扰动的一致和物理治疗，在我们的例子中，使用统一的暗区避免了幽灵行为。我们对CMB、大尺度结构和红移空间畸变观测数据进行了建模，并发现与CPL的差异大多很小，这表明尽管第四阶段CMB和星系调查将能够测试这些模型，但在线性尺度上实现它们之间的决定性区别可能是具有挑战性的。在非线性水平上，我们研究了UDF中的球形坍塌，并表明在这个框架内，结构形成的过程与标准场景非常相似。利用普朗克、DESI BAO DR2和DES Y5超新星数据，我们证明了这个简单的UDF模型几乎和CPL一样适合当前的观测结果，同时一致地处理了扰动。由于大多数宇宙学观测对暗扇区如何分裂并不敏感，统一框架还可以近似暗能量-暗物质相互作用场景或暗物质演化的现象学，使其成为一种通用的数据建模方法，至少只要暗成分具有消失的声速，这是我们分析中最显著的特征。我们的研究结果强调，具有演化状态方程和零声速的统一暗流体足以通过电流约束而不调用幻相组件。
{"title":"Unified dark fluid with null sound speed as an alternative to phantom dark energy","authors":"Raphaël Kou and Antony Lewis","doi":"10.1088/1475-7516/2026/01/014","DOIUrl":"https://doi.org/10.1088/1475-7516/2026/01/014","url":null,"abstract":"Recent BAO measurements from DESI, when combined with CMB and supernovae data, suggest evolving dark energy and in particular point to a possible phantom regime, with an equation of state parameter w < -1. This behaviour is theoretically problematic, as it violates the null energy condition and typically leads to instabilities in the perturbations. We explore an alternative phenomenological way to model dark matter and dark energy based on a unified dark fluid (UDF). By construction, our model reproduces the same background expansion history as DESI's best-fit using the Chevallier–Polarski–Linder (CPL) parametrization, but assumes a vanishing rest-frame sound speed and no anisotropic stress. This simple prescription ensures a consistent and physical treatment of perturbations and, in our case, the use of a unified dark sector avoids phantom behaviour. We model CMB, large-scale structure, and redshift-space distortion observables, and find mostly small differences with CPL, suggesting that while stage IV CMB and galaxy surveys will be able to test these models, achieving a decisive distinction between them may prove challenging on linear scales. At the non-linear level, we study spherical collapse in the UDF and show that within this framework, structure formation proceeds very similarly to standard scenarios. Using Planck, DESI BAO DR2, and DES Y5 supernovae data, we demonstrate that this simple UDF model fits current observations nearly as well as CPL, while treating perturbations consistently. Because most cosmological observations are not sensitive to how the dark sector is split, the unified framework can also approximate the phenomenology of interacting dark energy–dark matter scenarios or evolving dark matter, making it a general way to model the data, at least as long as the dark components have a vanishing sound speed, which is the most distinctive feature of our analysis. Our results highlight that a unified dark fluid with evolving equation of state and null sound speed is sufficient to pass current constraints without invoking a phantom component.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"38 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145897731","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}
Pub Date : 2026-01-05DOI: 10.1088/1475-7516/2026/01/018
Heena Ali and Sushant G. Ghosh
We investigate the shadow of Kerr-Bertotti-Robinson black holes (KBRBHs), which have a deviation parameter B that captures the effect of an external magnetic field on the spacetime geometry. These spacetimes of Petrov type D are asymptotically non-flat. We utilise the separability of the Hamilton-Jacobi equation to generate null geodesics and examine the crucial impact parameters for unstable photon orbits that define the black hole shadow. We carefully investigate how the magnetic field strength B and spin parameter a influence black hole shadows, discovering that increasing B increases the shadow size while also introducing additional distortions, especially at high spins. We calculate the shadow observables, viz., area A and oblateness D and create contour plots in the parameter space (a, B) to facilitate parameter estimation. We also investigate the dependence of the shadow on the observer's position, specifically by altering the radial coordinate rO and the inclination angle θ. For far viewers, the shadow approaches its asymptotic shape, but finite-distance observers perceive substantial deviations. The energy emission rate analysis reveals that the magnetic field parameter B modifies the Hawking radiation spectrum, with increasing B suppressing emission via backreaction, which lowers the Hawking temperature. Our findings confirm that KBRBH shadows encode imprints of magnetic deviations, thereby offering a potential avenue to distinguish Kerr from non-Kerr spacetimes and to probe magnetic effects in the strong-gravity regime.
{"title":"Parameter estimation of Kerr-Bertotti-Robinson black holes using their shadows","authors":"Heena Ali and Sushant G. Ghosh","doi":"10.1088/1475-7516/2026/01/018","DOIUrl":"https://doi.org/10.1088/1475-7516/2026/01/018","url":null,"abstract":"We investigate the shadow of Kerr-Bertotti-Robinson black holes (KBRBHs), which have a deviation parameter B that captures the effect of an external magnetic field on the spacetime geometry. These spacetimes of Petrov type D are asymptotically non-flat. We utilise the separability of the Hamilton-Jacobi equation to generate null geodesics and examine the crucial impact parameters for unstable photon orbits that define the black hole shadow. We carefully investigate how the magnetic field strength B and spin parameter a influence black hole shadows, discovering that increasing B increases the shadow size while also introducing additional distortions, especially at high spins. We calculate the shadow observables, viz., area A and oblateness D and create contour plots in the parameter space (a, B) to facilitate parameter estimation. We also investigate the dependence of the shadow on the observer's position, specifically by altering the radial coordinate rO and the inclination angle θ. For far viewers, the shadow approaches its asymptotic shape, but finite-distance observers perceive substantial deviations. The energy emission rate analysis reveals that the magnetic field parameter B modifies the Hawking radiation spectrum, with increasing B suppressing emission via backreaction, which lowers the Hawking temperature. Our findings confirm that KBRBH shadows encode imprints of magnetic deviations, thereby offering a potential avenue to distinguish Kerr from non-Kerr spacetimes and to probe magnetic effects in the strong-gravity regime.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"128 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145897705","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}
Pub Date : 2026-01-05DOI: 10.1088/1475-7516/2026/01/015
Amy Wayland, David Alonso and Adrien La Posta
We examine, from first principles, the angular power spectrum between the kinematic Sunyaev-Zel'dovich effect (kSZ) and the reconstructed galaxy momentum — the basis of existing and future “kSZ stacking” analyses. We present a comprehensive evaluation of all terms contributing to this cross-correlation, including both the transverse and longitudinal modes of the density-weighted velocity field, as well as all irreducible correlators that contribute to the momentum power spectrum. This includes the dominant component, involving the convolution of the electron-galaxy and velocity-velocity power spectra, an additional disconnected cross-term, and a connected non-Gaussian trispectrum term. Using this framework, we examine the impact of other commonly neglected contributions, such as the two-halo component of the dominant term, and the impact of satellite galaxies. Finally, we assess the sensitivity of upcoming CMB experiments to these effects and determine that they will be sensitive to the cross-term, the connected non-Gaussian trispectrum term, the two-halo contribution and impact of satellite galaxies, at a significance level of ∼ 4-6σ. On the other hand, the contribution from longitudinal modes is negligible in all cases. These results identify the astrophysical observables that must be accurately modelled to obtain unbiased constraints on cosmology and astrophysics from near-future kSZ measurements.
{"title":"Detailed theoretical modelling of the kinetic Sunyaev-Zel'dovich stacking power spectrum","authors":"Amy Wayland, David Alonso and Adrien La Posta","doi":"10.1088/1475-7516/2026/01/015","DOIUrl":"https://doi.org/10.1088/1475-7516/2026/01/015","url":null,"abstract":"We examine, from first principles, the angular power spectrum between the kinematic Sunyaev-Zel'dovich effect (kSZ) and the reconstructed galaxy momentum — the basis of existing and future “kSZ stacking” analyses. We present a comprehensive evaluation of all terms contributing to this cross-correlation, including both the transverse and longitudinal modes of the density-weighted velocity field, as well as all irreducible correlators that contribute to the momentum power spectrum. This includes the dominant component, involving the convolution of the electron-galaxy and velocity-velocity power spectra, an additional disconnected cross-term, and a connected non-Gaussian trispectrum term. Using this framework, we examine the impact of other commonly neglected contributions, such as the two-halo component of the dominant term, and the impact of satellite galaxies. Finally, we assess the sensitivity of upcoming CMB experiments to these effects and determine that they will be sensitive to the cross-term, the connected non-Gaussian trispectrum term, the two-halo contribution and impact of satellite galaxies, at a significance level of ∼ 4-6σ. On the other hand, the contribution from longitudinal modes is negligible in all cases. These results identify the astrophysical observables that must be accurately modelled to obtain unbiased constraints on cosmology and astrophysics from near-future kSZ measurements.","PeriodicalId":15445,"journal":{"name":"Journal of Cosmology and Astroparticle Physics","volume":"19 1","pages":""},"PeriodicalIF":6.4,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145897724","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}
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