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1. Multimessenger constraints on the neutron-star equation of state and the Hubble constant

   https://doi.org/10.1126/science.abb4317  

   Dietrich, Tim; Coughlin, Michael W.; Pang, Peter T. H.; Bulla, Mattia; Heinzel, Jack; Issa, Lina; Tews, Ingo; Antier, Sarah (December 2020, Science)

   Observations of neutron-star mergers with distinct messengers, including gravitational waves and electromagnetic signals, can be used to study the behavior of matter denser than an atomic nucleus and to measure the expansion rate of the Universe as quantified by the Hubble constant. We performed a joint analysis of the gravitational-wave event GW170817 with its electromagnetic counterparts AT2017gfo and GRB170817A, and the gravitational-wave event GW190425, both originating from neutron-star mergers. We combined these with previous measurements of pulsars using x-ray and radio observations, and nuclear-theory computations using chiral effective field theory, to constrain the neutron-star equation of state. We found that the radius of a 1.4–solar mass neutron star is ${11.75}_{-0.81}^{+0.86}$km at 90% confidence and the Hubble constant is ${66.2}_{-4.2}^{+4.4}$at 1σ uncertainty. 

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2. Short GRB Host Galaxies. II. A Legacy Sample of Redshifts, Stellar Population Properties, and Implications for Their Neutron Star Merger Origins

   https://doi.org/10.3847/1538-4357/ac91d1  

   Nugent, Anya E.; Fong, Wen-Fai; Dong 董, Yuxin 雨欣; Leja, Joel; Berger, Edo; Zevin, Michael; Chornock, Ryan; Cobb, Bethany E.; Kelley, Luke Zoltan; Kilpatrick, Charles D.; et al (November 2022, The Astrophysical Journal)

   Abstract We present the stellar population properties of 69 short gamma-ray burst (GRB) host galaxies, representing the largest uniformly modeled sample to date. Using theProspectorstellar population inference code, we jointly fit photometry and/or spectroscopy of each host galaxy. We find a population median redshift of $z={0.64}_{-0.32}^{+0.83}$(68% confidence), including nine photometric redshifts atz≳ 1. We further find a median mass-weighted age oft_m= ${0.8}_{-0.53}^{+2.71}$Gyr, stellar mass of log(M_*/M_⊙) = ${9.69}_{-0.65}^{+0.75}$, star formation rate of SFR = ${1.44}_{-1.35}^{+9.37}$M_⊙yr⁻¹, stellar metallicity of log(Z_*/Z_⊙) = $-{0.38}_{-0.42}^{+0.44}$, and dust attenuation of $A_V={0.43}_{-0.36}^{+0.85}$mag (68% confidence). Overall, the majority of short GRB hosts are star-forming (≈84%), with small fractions that are either transitioning (≈6%) or quiescent (≈10%); however, we observe a much larger fraction (≈40%) of quiescent and transitioning hosts atz≲ 0.25, commensurate with galaxy evolution. We find that short GRB hosts populate the star-forming main sequence of normal field galaxies, but do not include as many high-mass galaxies as the general galaxy population, implying that their binary neutron star (BNS) merger progenitors are dependent on a combination of host star formation and stellar mass. The distribution of ages and redshifts implies a broad delay-time distribution, with a fast-merging channel atz> 1 and a decreased neutron star binary formation efficiency from high to low redshifts. If short GRB hosts are representative of BNS merger hosts within the horizon of current gravitational wave detectors, these results can inform future searches for electromagnetic counterparts. All of the data and modeling products are available on the Broadband Repository for Investigating Gamma-ray burst Host Traits website. 

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3. Updated Observing Scenarios and Multimessenger Implications for the International Gravitational-wave Networks O4 and O5

   https://doi.org/10.3847/1538-4357/acfcb1  

   Kiendrebeogo, R. Weizmann; Farah, Amanda M.; Foley, Emily M.; Gray, Abigail; Kunert, Nina; Puecher, Anna; Toivonen, Andrew; VandenBerg, R. Oliver; Anand, Shreya; Ahumada, Tomás; et al (November 2023, The Astrophysical Journal)

   An advanced LIGO and Virgo’s third observing run brought another binary neutron star merger (BNS) and the first neutron-star black hole mergers. While no confirmed kilonovae were identified in conjunction with any of these events, continued improvements of analyses surrounding GW170817 allow us to project constraints on the Hubble Constant (H₀), the Galactic enrichment fromr-process nucleosynthesis, and ultra-dense matter possible from forthcoming events. Here, we describe the expected constraints based on the latest expected event rates from the international gravitational-wave network and analyses of GW170817. We show the expected detection rate of gravitational waves and their counterparts, as well as how sensitive potential constraints are to the observed numbers of counterparts. We intend this analysis as support for the community when creating scientifically driven electromagnetic follow-up proposals. During the next observing run O4, we predict an annual detection rate of electromagnetic counterparts from BNS of ${0.43}_{-0.26}^{+0.58}$( ${1.97}_{-1.2}^{+2.68}$) for the Zwicky Transient Facility (Rubin Observatory). 

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4. Measurement of the inclusive isolated-photon production cross section in pp collisions at $$\mathbf {\sqrt{\textit{s}}=13}$$ TeV

   https://doi.org/10.1140/epjc/s10052-024-13506-x  

   Acharya, S; Adamová, D; Agarwal, A; Aglieri_Rinella, G; Aglietta, L; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; et al (January 2025, The European Physical Journal C)

   Abstract The production cross section of inclusive isolated photons has been measured by the ALICE experiment at the CERN LHC in pp collisions at centre-of-momentum energy of$$\sqrt{s} =13$$ $\sqrt{s}=13$ TeV collected during the LHC Run 2 data-taking period. The measurement is performed by combining the measurements of the electromagnetic calorimeter EMCal and the central tracking detectors ITS and TPC, covering a pseudorapidity range of$$|\eta ^{\gamma }|<0.67$$ $|{\eta }^{\gamma }|<0.67$and a transverse momentum range of$$7 $7<p_{\text{T}}^{\gamma }<200$GeV/$$c$$ $c$. The result extends to lower$$p_\textrm{T}^{\gamma }$$ $p_{\text{T}}^{\gamma }$and$$x_\textrm{T}^{\gamma } = 2p_\textrm{T}^{\gamma }/\sqrt{s} $$ $x_{\text{T}}^{\gamma }=2p_{\text{T}}^{\gamma }/\sqrt{s}$ranges, the lowest$$x_\textrm{T}^{\gamma }$$ $x_{\text{T}}^{\gamma }$of any isolated photon measurements to date, extending significantly those measured by the ATLAS and CMS experiments towards lower$$p_\textrm{T}^{\gamma }$$ $p_{\text{T}}^{\gamma }$at the same collision energy with a small overlap between the measurements. The measurement is compared with next-to-leading order perturbative QCD calculations and the results from the ATLAS and CMS experiments as well as with measurements at other collision energies. The measurement and theory prediction are in agreement with each other within the experimental and theoretical uncertainties. 

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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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