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1. Search for dark matter produced in association with a single top quark and an energetic W boson in $$\sqrt{s}=$$ 13 TeV $$pp$$ collisions with the ATLAS detector

   https://doi.org/10.1140/epjc/s10052-023-11582-z  

   Aad, G. ; Abbott, B. ; Abbott, D. C. ; Abeling, K. ; Abidi, S. H. ; Aboulhorma, A. ; Abramowicz, H. ; Abreu, H. ; Abulaiti, Y. ; Hoffman, A. C. ; et al ( July 2023 , The European Physical Journal C)

   This paper presents a search for dark matter,$$\chi $$$\chi$, using events with a single top quark and an energeticWboson. The analysis is based on proton–proton collision data collected with the ATLAS experiment at$$\sqrt{s}=$$$\sqrt{s}=$13 TeV during LHC Run 2 (2015–2018), corresponding to an integrated luminosity of 139 fb$$^{-1}$$${}^{-1}$. The search considers final states with zero or one charged lepton (electron or muon), at least oneb-jet and large missing transverse momentum. In addition, a result from a previous search considering two-charged-lepton final states is included in the interpretation of the results. The data are found to be in good agreement with the Standard Model predictions and the results are interpreted in terms of 95% confidence-level exclusion limits in the context of a class of dark matter models involving an extended two-Higgs-doublet sector together with a pseudoscalar mediator particle. The search is particularly sensitive to on-shell production of the charged Higgs boson state,$$H^{\pm }$$$H^{\pm }$, arising from the two-Higgs-doublet mixing, and its semi-invisible decays via the mediator particle,a:$$H^{\pm } \rightarrow W^\pm a (\rightarrow \chi \chi )$$$H^{\pm }\to W^{\pm }a(\to \chi \chi )$. Signal models with$$H^{\pm }$$$H^{\pm }$masses up to 1.5 TeV andamasses up to 350 GeV are excluded assuming a$$\tan \beta $$$tan\beta$value of 1. For masses ofaof 150 (250) GeV,$$\tan \beta $$$tan\beta$values up to 2 are excluded for$$H^{\pm }$$$H^{\pm }$masses between 200 (400) GeV and 1.5 TeV. Signals with$$\tan \beta $$$tan\beta$values between 20 and 30 are excluded for$$H^{\pm }$$$H^{\pm }$masses between 500 and 800 GeV.

    

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2. Molecular polariton electroabsorption

   https://doi.org/10.1038/s41467-022-35589-4  

   Cheng, Chiao-Yu ; Krainova, Nina ; Brigeman, Alyssa N. ; Khanna, Ajay ; Shedge, Sapana ; Isborn, Christine ; Yuen-Zhou, Joel ; Giebink, Noel C. ( December 2022 , Nature Communications)

   We investigate electroabsorption (EA) in organic semiconductor microcavities to understand whether strong light-matter coupling non-trivially alters their nonlinear optical [$${\chi }^{(3)}\left(\omega,{{{{\mathrm{0,0}}}}}\right)$$${\chi }^{\left(3\right)}\left(\omega ,\mathrm{0,\; 0}\right)$] response. Focusing on strongly-absorbing squaraine (SQ) molecules dispersed in a wide-gap host matrix, we find that classical transfer matrix modeling accurately captures the EA response of low concentration SQ microcavities with a vacuum Rabi splitting of$$\hslash \Omega \approx 200$$$\hslash \Omega \approx 200$meV, but fails for high concentration cavities with$$\hslash \Omega \approx 420$$$\hslash \Omega \approx 420$meV. Rather than new physics in the ultrastrong coupling regime, however, we attribute the discrepancy at high SQ concentration to a nearly dark H-aggregate state below the SQ exciton transition, which goes undetected in the optical constant dispersion on which the transfer matrix model is based, but nonetheless interacts with and enhances the EA response of the lower polariton mode. These results indicate that strong coupling can be used to manipulate EA (and presumably other optical nonlinearities) from organic microcavities by controlling the energy of polariton modes relative to other states in the system, but it does not alter the intrinsic optical nonlinearity of the organic semiconductor inside the cavity.

    

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3. Searching for a dark matter particle with anti-protonic atoms

   https://doi.org/10.1140/epjc/s10052-023-12319-8  

   Doser, Michael ; Farrar, Glennys ; Kornakov, Georgy ( December 2023 , The European Physical Journal C)

   A wide range of dark matter candidates have been proposed and are actively being searched for in a large number of experiments, both at high (TeV) and low (sub meV) energies. One dark matter candidate, a deeply bounduuddsssexaquark,$$S$$$S$, with mass$$\sim 2$$$\sim 2$GeV (having the same quark content as the hypothesized H-dibaryon, but long lived) is particularly difficult to explore experimentally. In this paper, we propose a scheme in which such a state could be produced at rest through the formation of$$\bar{p}$$$\overline{p}$–$$^3$$${}^3$He antiprotonic atoms and their annihilation into$$S$$$S$+$$K^+K^+\pi ^-$$$K^{+}{K}^{+}{\pi }^{-}$, identified both through the unique tag of a$$S=+2, Q=+1$$$S=+2,Q=+1$final state, as well as through full kinematic reconstruction of the final state recoiling against it.

    

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4. Search strategy for gluinos at the LHC with a Higgs boson decaying into tau leptons

   https://doi.org/10.1140/epjc/s10052-022-10951-4  

   Arganda, Ernesto ; Delgado, Antonio ; Morales, Roberto A. ; Quirós, Mariano ( October 2022 , The European Physical Journal C)

   The possibility in supersymmetric scenarios that the dark matter candidate is a Higgsino-like neutralino means that its production can be associated with Higgs bosons. Taking advantage of this fact, we propose a LHC search strategy for gluinos with$$\tau $$$\tau$leptons in the final state, coming from the decay of a Higgs boson. We consider the strong production of a pair of gluinos, one of which decays into the Higgsino plus jets while the other decays into the bino plus jets. In turn, this bino decays into the Higgsino plus a Higgs boson which finally decays into a$$\tau $$$\tau$-lepton pair. Therefore, the experimental signature under study consists of 4 jets, 2$$\tau $$$\tau$leptons, and a large amount of missing transverse energy. This work represents a proof of principle of a search that is sensitive to a spectrum such that the gluino does not directly decay to the dark matter candidate but to an intermediate electroweakino that then produces Higgs bosons in its subsequent decay. Our cut-based search strategy allows us to reach, for a LHC center-of-mass energy of 14 TeV and a total integrated luminosity of 1 ab$$^{-1}$$${}^{-1}$, significances of up to 2 standard deviations, considering systematic uncertainties in the SM background of 30%. The projections for 3 ab$$^{-1}$$${}^{-1}$are encouraging, with significances at the evidence level, which in more optimistic experimental scenarios could exceed 4 standard deviations.

    

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5. Exploration of a singular fluid spacetime

   https://doi.org/10.1007/s10714-021-02873-5  

   Remmen, Grant N. ( November 2021 , General Relativity and Gravitation)

   We investigate the properties of a special class of singular solutions for a self-gravitating perfect fluid in general relativity: the singular isothermal sphere. For arbitrary constant equation-of-state parameter$$w=p/\rho $$$w=p/\rho$, there exist static, spherically-symmetric solutions with density profile$$\propto 1/r^2$$$\propto 1/r^2$, with the constant of proportionality fixed to be a special function ofw. Like black holes, singular isothermal spheres possess a fixed mass-to-radius ratio independent of size, but no horizon cloaking the curvature singularity at$$r=0$$$r=0$. For$$w=1$$$w=1$, these solutions can be constructed from a homogeneous dilaton background, where the metric spontaneously breaks spatial homogeneity. We study the perturbative structure of these solutions, finding the radial modes and tidal Love numbers, and also find interesting properties in the geodesic structure of this geometry. Finally, connections are discussed between these geometries and dark matter profiles, the double copy, and holographic entropy, as well as how the swampland distance conjecture can obscure the naked singularity.

    

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