De Romeri, V., Karamitros, D., Lebedev, O., & Toma, T. (2020). Neutrino dark matter and the Higgs portal: improved freeze-in analysis. J. High Energy Phys., 10(10), 137–41pp.
Abstract: Sterile neutrinos are one of the leading dark matter candidates. Their masses may originate from a vacuum expectation value of a scalar field. If the sterile neutrino couplings are very small and their direct coupling to the inflaton is forbidden by the lepton number symmetry, the leading dark matter production mechanism is the freeze-in scenario. We study this possibility in the neutrino mass range up to 1 GeV, taking into account relativistic production rates based on the Bose-Einstein statistics, thermal masses and phase transition effects. The specifics of the production mechanism and the dominant mode depend on the relation between the scalar and sterile neutrino masses as well as on whether or not the scalar is thermalized. We find that the observed dark matter abundance can be produced in all of the cases considered. We also revisit the freeze-in production of a Higgs portal scalar, pointing out the importance of a fusion mode, as well as the thermalization constraints.
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de Anda, F. J., Antoniadis, I., Valle, J. W. F., & Vaquera-Araujo, C. A. (2020). Scotogenic dark matter in an orbifold theory of flavor. J. High Energy Phys., 10(10), 190–13pp.
Abstract: We propose a flavour theory in which the family symmetry results naturally from a six-dimensional orbifold compactification. “Diracness” of neutrinos is a consequence of the spacetime dimensionality, and the fact that right-handed neutrinos live in the bulk. Dark matter is incorporated in a scotogenic way, as a result of an auxiliary Z(3) symmetry, and its stability is associated to the conservation of a “dark parity” symmetry. The model leads naturally to a “golden” quark-lepton mass relation.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Searches for low-mass dimuon resonances. J. High Energy Phys., 10(10), 156–26pp.
Abstract: Searches are performed for a low-mass dimuon resonance, X, produced in proton-proton collisions at a center-of-mass energy of 13 TeV, using a data sample corresponding to an integrated luminosity of 5.1 fb(-1) and collected with the LHCb detector. The X bosons can either decay promptly or displaced from the proton-proton collision, where in both cases the requirements placed on the event and the assumptions made about the production mechanisms are kept as minimal as possible. The searches for promptly decaying X bosons explore the mass range from near the dimuon threshold up to 60 GeV, with nonnegligible X widths considered above 20 GeV. The searches for displaced X -> μ(+)mu (-) decays consider masses up to 3 GeV. None of the searches finds evidence for a signal and 90% confidence-level exclusion limits are placed on the X -> μ(+)mu (-) cross sections, each with minimal model dependence. In addition, these results are used to place world-leading constraints on GeV-scale bosons in the two-Higgs-doublet and hidden-valley scenarios.
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Penalva, N., Hernandez, E., & Nieves, J. (2021). The role of right-handed neutrinos in b -> c tau (pi nu(tau), rho nu(tau), mu(nu)over-bar(mu)nu(tau))(nu)over-bar(tau) from visible final-state kinematics. J. High Energy Phys., 10(10), 122–45pp.
Abstract: In the context of lepton flavor universality violation (LFUV) studies, we fully derive a general tensor formalism to investigate the role that left- and right-handed neutrino new-physics (NP) terms may have in b -> c tau(nu) over bar (tau) transitions. We present, for several extensions of the Standard Model (SM), numerical results for the Lambda(b) -> Lambda(c)tau(nu) over bar (tau) semileptonic decay, which is expected to be measured with precision at the LHCb. This reaction can be a new source of experimental information that can help to confirm, or maybe rule out, LFUV presently seen in (B) over bar meson decays. The present study analyzes observables that can help in distinguishing between different NP scenarios that otherwise provide very similar results for the branching ratios, which are our currently best hints for LFUV. Since the tau lepton is very short-lived, we consider three subsequent tau-decay modes, two hadronic pi nu(tau) and rho nu(tau) and one leptonic mu(nu) over bar (mu)nu(tau), which have been previously studied for (B) over bar -> D(*) decays. Within the tensor formalism that we have developed in previous works, we re-obtain the expressions for the differential decay width written in terms of visible (experimentally accessible) variables of the massive particle created in the tau decay. There are seven different tau angular and spin asymmetries that are defined in this way and that can be extracted from experiment. Those asymmetries provide observables that can help in constraining possible SM extensions.
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Eberhardt, O., Miralles, V., & Pich, A. (2021). Constraints on coloured scalars from global fits. J. High Energy Phys., 10(10), 123–23pp.
Abstract: We consider a simple extension of the electroweak theory, incorporating one SU(2)(L) doublet of colour-octet scalars with Yukawa couplings satisfying the principle of minimal flavour violation. Using the HEPfit package, we perform a global fit to the available data, including all relevant theoretical constraints, and extract the current bounds on the model parameters. Coloured scalars with masses below 1.05 TeV are already excluded, provided they are not fermiophobic. The mass splittings among the different (charged and CP-even and CP-odd neutral) scalars are restricted to be smaller than 20 GeV. Moreover, for scalar masses smaller than 1.5 TeV, the Yukawa coupling of the coloured scalar multiplet to the top quark cannot exceed the one of the SM Higgs doublet by more than 80%. These conclusions are quite generic and apply in more general frameworks (without fine tunings). The theoretical requirements of perturbative unitarity and vacuum stability enforce relevant constraints on the quartic scalar potential parameters that are not yet experimentally tested.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., Cabrera Urban, S., et al. (2023). Search for leptoquarks decaying into the bt final state in pp collisions at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 10(10), 001–55pp.
Abstract: A search for leptoquarks decaying into the b tau final state is performed using Run 2 proton-proton collision data from the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb(-1) at root s = 13TeV recorded by the ATLAS detector. The benchmark models considered in this search are vector leptoquarks with electric charge of 2/3e and scalar leptoquarks with an electric charge of 4/3e. No significant excess above the Standard Model prediction is observed, and 95% confidence level upper limits are set on the cross-section times branching fraction of leptoquarks decaying into b tau. For the vector leptoquark production two models are considered: the Yang-Mills and Minimal coupling models. In the Yang-Mills (Minimal coupling) scenario, vector leptoquarks with a mass below 1.58 (1.35) TeV are excluded for a gauge coupling of 1.0 and below 2.05 (1.99) TeV for a gauge coupling of 2.5. In the case of scalar leptoquarks, masses below 1.28 (1.53) TeV are excluded for a Yukawa coupling of 1.0 (2.5). Finally, an interpretation of the results with minimal model dependence is performed for each of the signal region categories, and limits on the visible cross-section for beyond the Standard Model processes are provided.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., Cabrera Urban, S., et al. (2023). Search for periodic signals in the dielectron and diphoton invariant mass spectra using 139 fb-1 of pp collisions at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 10(10), 079–51pp.
Abstract: A search for physics beyond the Standard Model inducing periodic signals in the dielectron and diphoton invariant mass spectra is presented using 139 fb(-1) of root s = 13 TeV pp collision data collected by the ATLAS experiment at the LHC. Novel search techniques based on continuous wavelet transforms are used to infer the frequency of periodic signals from the invariant mass spectra and neural network classifiers are used to enhance the sensitivity to periodic resonances. In the absence of a signal, exclusion limits are placed at the 95% confidence level in the two-dimensional parameter space of the clockwork gravity model. Model-independent searches for deviations from the background-only hypothesis are also performed.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2012). Search for a standard model Higgs boson in the H -> ZZ -> l(+)l(-) nu(nu)over-bar decay channel using 4.7 fb(-1) of root s=7 TeV data with the ATLAS detector. Phys. Lett. B, 717(1-3), 29–48.
Abstract: A search for a Standard Model Higgs boson decaying via H -> ZZ -> l(+)l(-) nu(nu) over bar, where l represents electrons or muons, is presented. It is based on proton-proton collision data at root s = 7 TeV, collected by the ATLAS experiment at the LHC during 2011 and corresponding to an integrated luminosity of 4.7 fb(-1). The data agree with the expected Standard Model backgrounds. Upper limits on the Higgs boson production cross section are derived for Higgs boson masses between 200 GeV and 600 GeV and the production of a Standard Model Higgs boson with a mass in the range 319-558 GeV is excluded at the 95% confidence level.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2012). Search for a Standard Model Higgs boson in the mass range 200-600 GeV in the H -> ZZ -> l(+)l(-)q(q)over-bar decay channel with the ATLAS detector. Phys. Lett. B, 717(1-3), 70–88.
Abstract: A search for a heavy Standard Model Higgs boson decaying via H -> ZZ -> l(+)l(-)q (q) over bar, where l = e or mu, is presented. The search uses a data set of pp collisions at root s = 7 TeV, corresponding to an integrated luminosity of 4.7 fb(-1) collected in 2011 by the ATLAS detector at the CERN LHC. No significant excess of events above the estimated background is found. Upper limits at 95% confidence level on the production cross section of a Higgs boson with a mass in the range between 200 and 600 GeV are derived. A Standard Model Higgs boson with a mass in the range 300 GeV <= m(H) 322 <= GeV or 353 GeV <= m(H) <= 410 GeV is excluded at 95% CL The corresponding expected exclusion range is 351 GeV <= m(H) <= 404 GeV at 95% CL.
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Cirigliano, V., Jenkins, J. P., & Gonzalez-Alonso, M. (2010). Semileptonic decays of light quarks beyond the Standard Model. Nucl. Phys. B, 830(1-2), 95–115.
Abstract: We describe non-standard contributions to semileptonic processes in a model independent way in terms of in SU(2)(L) x U(1)(Y) invariant effective lagrangian at the weak scale, front which we derive the low-energy effective lagrangian governing muon and beta decays. We find that the deviation from Cabibbo universality, Delta(CKM) equivalent to vertical bar V-ud vertical bar(2) + vertical bar V-us vertical bar(2) + vertical bar V-ub vertical bar(2) – 1, receives contributions from four effective operators. The phenomenological bound Delta(CKM) = (-1 +/- 6) x 10(-4) provides strong constraints on all four operators, corresponding to art effective scale Lambda > 11 TeV (90% CL). Depending on the operator, this constraint is at the same level or better then the Z pole observables. Conversely, precision electroweak constraints alone would allow universality violations as large as Delta(CKM) = -0.01 (90% CL). An observed Delta(CKM) not equal 0 at this level Could be explained in terms of a single four-fermion operator which is relatively poorly constrained by electroweak precision measurements.
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