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1. Constraints on $f\left(R\right)$ gravity from thermal-Sunyaev-Zel’dovich-effect-selected SPT galaxy clusters and weak lensing mass calibration from DES and HST

   https://doi.org/10.1103/PhysRevD.111.043519  

   Vogt, S_M L; Bocquet, S; Davies, C T; Mohr, J J; Schmidt, F; Ruan, C-Z; Li, B; Hernández-Aguayo, C; Grandis, S; Bleem, L E; et al (February 2025, Physical Review D)

   We present constraints on the $f\left(R\right)$gravity model using a sample of 1005 galaxy clusters in the redshift range 0.25–1.78 that have been selected through the thermal Sunyaev-Zel’dovich effect from South Pole Telescope data and subjected to optical and near-infrared confirmation with the multicomponent matched filter algorithm. We employ weak gravitational lensing mass calibration from the Dark Energy Survey Year 3 data for 688 clusters at $z<0.95$and from the Hubble Space Telescope for 39 clusters with $0.6<z<1.7$. Our cluster sample is a powerful probe of $f\left(R\right)$gravity, because this model predicts a scale-dependent enhancement in the growth of structure, which impacts the halo mass function (HMF) at cluster mass scales. To account for these modified gravity effects on the HMF, our analysis employs a semianalytical approach calibrated with numerical simulations. Combining calibrated cluster counts with primary cosmic microwave background temperature and polarization anisotropy measurements from the Planck 2018 release, we derive robust constraints on the $f\left(R\right)$parameter $f_{R0}$. Our results, ${\log }_{10}\left|f_{R0}\right|<-5.32$at the 95% credible level, are the tightest current constraints on $f\left(R\right)$gravity from cosmological scales. This upper limit rules out $f\left(R\right)$-like deviations from general relativity that result in more than a $\sim 20\%$enhancement of the cluster population on mass scales $M_{200\mathrm{c}}>3\times {10}^{14}{M}_{\odot }$. Published by the American Physical Society2025 

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2. Constraints on the Hubble constant from supernova Refsdal’s reappearance

   https://doi.org/10.1126/science.abh1322  

   Kelly, Patrick L.; Rodney, Steven; Treu, Tommaso; Oguri, Masamune; Chen, Wenlei; Zitrin, Adi; Birrer, Simon; Bonvin, Vivien; Dessart, Luc; Diego, Jose M.; et al (June 2023, Science)

   The gravitationally lensed supernova Refsdal appeared in multiple images produced through gravitational lensing by a massive foreground galaxy cluster. After the supernova appeared in 2014, lens models of the galaxy cluster predicted that an additional image of the supernova would appear in 2015, which was subsequently observed. We use the time delays between the images to perform a blinded measurement of the expansion rate of the Universe, quantified by the Hubble constant (H₀). Using eight cluster lens models, we infer $H_0={64.8}_{-4.3}^{+4.4}\text{ kilometers per second per megaparsec}$. Using the two models most consistent with the observations, we find $H_0={66.6}_{-3.3}^{+4.1}\text{ kilometers per second per megaparsec}$. The observations are best reproduced by models that assign dark-matter halos to individual galaxies and the overall cluster. 

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3. Star formation beyond galaxies: widespread in-situ formation of intra-cluster stars

   https://doi.org/10.33232/001c.127132  

   Ahvazi, Niusha; Sales, Laura V; Navarro, Julio F; Benson, Andrew; Boselli, Alessandro; D'Souza, Richard (January 2024, The Open Journal of Astrophysics)

   We study the fraction of the intra-cluster light (ICL) formed in-situ in the three most massive clusters of the TNG50 simulation, with virial masses $\sim {10}^{14}$. We find that a significant fraction of ICL stars ( $8\%$- $28\%$) are born in-situ. This amounts to a total stellar mass comparable to the central galaxy itself. Contrary to simple expectations, only a sub-dominant fraction of these in-situ ICL stars are born in the central regions and later re-distributed to more energetic orbits during mergers. Instead, many in-situ ICL stars form directly hundreds of kiloparsecs away from the central galaxy, in clouds condensing out of the circum-cluster medium. The simulations predict a present-date diffuse star formation rate of $$1 ${\mathrm{M}}_{\odot }$/yr, with higher rates at higher redshifts. The diffuse star forming component of the ICL is filamentary in nature, extends for hundreds of kiloparsecs and traces the distribution of neutral gas in the cluster host halo. We discuss briefly how numerical details of the baryonic treatment in the simulation, in particular the density threshold for star formation and the equation of state, may play a role in this result. We conclude that a sensitivity of $1.6\times {10}^{-19}-2.6\times {10}^{-18}$erg s ${}^{-1}$cm ${}^{-2}$arcsec ${}^{-2}$in H ${}_{\alpha }$flux (beyond current observational capabilities) would be necessary to detect this diffuse star-forming component in galaxy clusters. 

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4. Enhanced dark matter abundance in first-order phase transitions

   https://doi.org/10.1103/PhysRevD.110.115005  

   Allahverdi, Rouzbeh; Hauptmann, Cash; Huang, Peisi (December 2024, Physical Review D)

   We propose a novel scenario to obtain the correct relic abundance for thermally underproduced dark matter. This scenario utilizes a strongly first-order phase transition at temperature $T_{\mathrm{PT}}$that gives rise to dark matter mass $m$. Freeze-out in the broken phase can yield the desired abundance in the entire region currently allowed by observational bounds and theoretical constraints for ${10}^2{T}_{\mathrm{PT}}\lesssim m\lesssim {10}^4{T}_{\mathrm{PT}}$. We show that the accompanying gravitational waves are strong enough to be detected by many upcoming and proposed experiments. This, in tandem with dark matter indirect searches, provides a multimessenger probe of such models. Positive signals in the future can help reconstruct the potential governing the phase transition and shed light on an underlying particle physics realization. Published by the American Physical Society2024 

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5. Searching for dark photon dark matter in LIGO O1 data

   https://doi.org/10.1038/s42005-019-0255-0  

   Guo, Huai-Ke; Riles, Keith; Yang, Feng-Wei; Zhao, Yue (December 2019, Communications Physics)

   Abstract Dark matter exists in our Universe, but its nature remains mysterious. The remarkable sensitivity of the Laser Interferometer Gravitational-Wave Observatory (LIGO) may be able to solve this mystery. A good dark matter candidate is the ultralight dark photon. Because of its interaction with ordinary matter, it induces displacements on LIGO mirrors that can lead to an observable signal. In a study that bridges gravitational wave science and particle physics, we perform a direct dark matter search using data from LIGO’s first (O1) data run, as opposed to an indirect search for dark matter via its production of gravitational waves. We demonstrate an achieved sensitivity on squared coupling as$$\sim\! 4\times 1{0}^{-45}$$ $~4\times 10^{-45}$, in a$$U{(1)}_{{\rm{B}}}$$ $U{\left(1\right)}_B$dark photon dark matter mass band around$${m}_{{\rm{A}}} \sim 4\,\times 1{0}^{-13}$$ $m_A~4\times 10^{-13}$eV. Substantially improved search sensitivity is expected during the coming years of continued data taking by LIGO and other gravitational wave detectors in a growing global network. 

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