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1. Measurement of the t$$ \overline{t} $$t$$ \overline{t} $$ production cross section in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector

   https://doi.org/10.1007/JHEP11(2021)118  

   Aad, G. ; Abbott, B. ; Abbott, D. C. ; Abed Abud, A. ; Abeling, K. ; Abhayasinghe, D. K. ; Abidi, S. H. ; Abramowicz, H. ; Abreu, H. ; Abulaiti, Y. ; et al ( November 2021 , Journal of High Energy Physics)

   A bstract A measurement of four-top-quark production using proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the Large Hadron Collider corresponding to an integrated luminosity of 139 fb − 1 is presented. Events are selected if they contain a single lepton (electron or muon) or an opposite-sign lepton pair, in association with multiple jets. The events are categorised according to the number of jets and how likely these are to contain b -hadrons. A multivariate technique is then used to discriminate between signal and background events. The measured four-top-quark production cross section is found to be $$ {26}_{-15}^{+17} $$ 26 − 15 + 17 fb, with a corresponding observed (expected) significance of 1.9 (1.0) standard deviations over the background-only hypothesis. The result is combined with the previous measurement performed by the ATLAS Collaboration in the multilepton final state. The combined four-top-quark production cross section is measured to be $$ {24}_{-6}^{+7} $$ 24 − 6 + 7 fb, with a corresponding observed (expected) signal significance of 4.7 (2.6) standard deviations over the background-only predictions. It is consistent within 2.0 standard deviations with the Standard Model expectation of 12 . 0 ± 2 . 4 fb. 

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2. Mixed EW-QCD two-loop amplitudes for $$ q\overline{q}\to {\mathrm{\ell}}^{+}{\mathrm{\ell}}^{-} $$ and γ5 scheme independence of multi-loop corrections

   https://doi.org/10.1007/JHEP05(2021)213  

   Heller, Matthias ; von Manteuffel, Andreas ; Schabinger, Robert M. ; Spiesberger, Hubert ( May 2021 , Journal of High Energy Physics)

   null (Ed.)

   A bstract We perform a dedicated study of the $$ q\overline{q} $$ q q ¯ -initiated two-loop electroweak-QCD Drell-Yan scattering amplitude in dimensional regularization schemes for vanishing light quark and lepton masses. For the relative order α and α s one-loop Standard Model corrections, details of our comparison to the original literature are given. The infrared pole terms of the mixed two-loop amplitude are governed by a known generalization of the dipole formula and we show explicitly that exactly the same two-loop polarized hard scattering functions are obtained in both the standard ’t Hooft-Veltman-Breitenlohner-Maison γ 5 scheme and Kreimer’s anticommuting γ 5 scheme. 

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3. Two-loop leading colour QCD corrections to $$ q\overline{q} $$ → γγg and qg → γγq

   https://doi.org/10.1007/JHEP04(2021)201  

   Agarwal, Bakul ; Buccioni, Federico ; von Manteuffel, Andreas ; Tancredi, Lorenzo ( April 2021 , Journal of High Energy Physics)

   null (Ed.)

   A bstract We present the leading colour and light fermionic planar two-loop corrections for the production of two photons and a jet in the quark-antiquark and quark-gluon channels. In particular, we compute the interference of the two-loop amplitudes with the corresponding tree level ones, summed over colours and polarisations. Our calculation uses the latest advancements in the algorithms for integration-by-parts reduction and multivariate partial fraction decomposition to produce compact and easy-to-use results. We have implemented our results in an efficient C++ numerical code. We also provide their analytic expressions in Mathematica format. 

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4. On representations of Gal(\overline{Q}/Q), \hat{GT} and Aut(\hat{F}_2).

   Bleher, Frauke M. ; Chinburg, Ted ; Lubotzky, Alexander ( June 2021 , Journal of algebra)

   By work of Belyi, the absolute Galois group G_Q of the rational numbers embeds into a subgroup \hat{GT} called the Grothendeick-Teichmuller group of the group A of continuous automorphisms of a profinite group on two generators. We show that a rich class of representations of G_Q lifts to \hat{GT} by showing they lift all the way to a finite index subgroup of A. 

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5. Search for resonant t t ¯ $$ \mathrm{t}\overline{\mathrm{t}} $$ production in proton-proton collisions at s = 13 $$ \sqrt{s}=13 $$ TeV

   https://doi.org/10.1007/JHEP04(2019)031  

   Sirunyan, A. M. ; Tumasyan, A. ; Adam, W. ; Ambrogi, F. ; Asilar, E. ; Bergauer, T. ; Brandstetter, J. ; Dragicevic, M. ; Erö, J. ; Escalante Del Valle, A. ; et al ( April 2019 , Journal of High Energy Physics)