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Radio observations of the 2022 outburst of the transitional Z-Atoll source XTE J1701-462

(2024)

Authors:

KVS Gasealahwe, IM Monageng, RP Fender, PA Woudt, AK Hughes, SE Motta, J van den Eijnden, P Saikia, E Tremou
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Catalog-based pseudo-$C_\ell$s

(2024)

Authors:

Kevin Wolz, David Alonso, Andrina Nicola
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Search for flavour-changing neutral-current couplings between the top quark and the Higgs boson in multi-lepton final states in 13 TeV pp collisions with the ATLAS detector

The European Physical Journal C SpringerOpen 84:7 (2024) 757

Authors:

G Aad, E Aakvaag, B Abbott, K Abeling, NJ Abicht, SH Abidi, M Aboelela, A Aboulhorma, H Abramowicz, H Abreu, Y Abulaiti, BS Acharya, A Ackermann, C Adam Bourdarios, L Adamczyk, SV Addepalli, MJ Addison, J Adelman, A Adiguzel, T Adye, AA Affolder, Y Afik, MN Agaras, J Agarwala

Abstract:

A search is presented for flavour-changing neutral-current interactions involving the top quark, the Higgs boson and an up-type quark (q=u, c) with the ATLAS detector at the Large Hadron Collider. The analysis considers leptonic decays of the top quark along with Higgs boson decays into two W bosons, two Z bosons or a τ+τ- pair. It focuses on final states containing either two leptons (electrons or muons) of the same charge or three leptons. The considered processes are tt¯ and Ht production. For the tt¯ production, one top quark decays via t→Hq. The proton–proton collision data set analysed amounts to (140fb-1) at (s=13TeV). No significant excess beyond Standard Model expectations is observed and upper limits are set on the t→Hq branching ratios at 95 % confidence level, amounting to observed (expected) limits of B(t→Hu)<2.8(3.0)×10-4 and B(t→Hc)<3.3(3.8)×10-4. Combining this search with other searches for tHq flavour-changing neutral-current interactions previously conducted by ATLAS, considering H→bb¯ and H→γγ decays, as well as H→τ+τ- decays with one or two hadronically decaying τ-leptons, yields observed (expected) upper limits on the branching ratios of B(t→Hu)<2.6(1.8)×10-4 and B(t→Hc)<3.4(2.3)×10-4.
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Search for short- and long-lived axion-like particles in H → a a → 4 γ decays with the ATLAS experiment at the LHC

The European Physical Journal C SpringerOpen 84:7 (2024) 742

Authors:

G Aad, B Abbott, K Abeling, NJ Abicht, SH Abidi, A Aboulhorma, H Abramowicz, H Abreu, Y Abulaiti, BS Acharya, C Adam Bourdarios, L Adamczyk, SV Addepalli, MJ Addison, J Adelman, A Adiguzel, T Adye, AA Affolder, Y Afik, MN Agaras, J Agarwala, A Aggarwal, C Agheorghiesei, A Ahmad

Abstract:

Presented is the search for anomalous Higgs boson decays into two axion-like particles (ALPs) using the full Run 2 data set of 140fb-1 of proton-proton collisions at a centre-of-mass energy of 13TeV recorded by the ATLAS experiment. The ALPs are assumed to decay into two photons, providing sensitivity to recently proposed models that could explain the (g-2)μ discrepancy. This analysis covers an ALP mass range from 100 to 62GeV and ALP-photon couplings in the range 10-7TeV-1
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A Radio Flare in the Long-lived Afterglow of the Distant Short GRB 210726A: Energy Injection or a Reverse Shock from Shell Collisions?

The Astrophysical Journal American Astronomical Society 970:2 (2024) 139

Authors:

Genevieve Schroeder, Lauren Rhodes, Tanmoy Laskar, Anya Nugent, Alicia Rouco Escorial, Jillian C Rastinejad, Wen-fai Fong, Alexander J van der Horst, Péter Veres, Kate D Alexander, Alex Andersson, Edo Berger, Peter K Blanchard, Sarah Chastain, Lise Christensen, Rob Fender, David A Green, Paul Groot, Ian Heywood, Assaf Horesh, Luca Izzo, Charles D Kilpatrick, Elmar Körding, Amy Lien

Abstract:

We present the discovery of the radio afterglow of the short gamma-ray burst (GRB) 210726A, localized to a galaxy at a photometric redshift of z ∼ 2.4. While radio observations commenced ≲1 day after the burst, no radio emission was detected until ∼11 days. The radio afterglow subsequently brightened by a factor of ∼3 in the span of a week, followed by a rapid decay (a “radio flare”). We find that a forward shock afterglow model cannot self-consistently describe the multiwavelength X-ray and radio data, and underpredicts the flux of the radio flare by a factor of ≈5. We find that the addition of substantial energy injection, which increases the isotropic kinetic energy of the burst by a factor of ≈4, or a reverse shock from a shell collision are viable solutions to match the broadband behavior. At z ∼ 2.4, GRB 210726A is among the highest-redshift short GRBs discovered to date, as well as the most luminous in radio and X-rays. Combining and comparing all previous radio afterglow observations of short GRBs, we find that the majority of published radio searches conclude by ≲10 days after the burst, potentially missing these late-rising, luminous radio afterglows.
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