1,720,989 research outputs found
Searches for vector-like quarks at future colliders and implications for composite Higgs models with dark matter
Full text linkMany composite Higgs models predict the existence of vector-like quarks with masses outside the reach of the LHC, e.g. mQ ≳ 2 TeV, in particular if these models contain a dark matter candidate. In such models the mass of the new resonances is bounded from above to satisfy the constraint from the observed relic density. We therefore develop new strategies to search for vector-like quarks at a future 100 TeV collider and evaluate what masses and interactions can be probed. We find that masses as large as ∼ 6.4 (∼9) TeV can be tested if the fermionic resonances decay into Standard Model (dark matter) particles. We also discuss the complementarity of dark matter searches, showing that most of the parameter space can be closed. On balance, this study motivates further the consideration of a higher-energy hadron collider for a next generation of facilities
Hunting for CP -violating axionlike particle interactions
Full text linkThe impact of axionlike particles (ALPs) on the search of permanent electric dipole moments (EDMs) of molecules, atoms, nuclei and nucleons is systematically investigated. Assuming the most general ALP effective field theory containing operators up to dimension-five, we evaluate the leading short-distance effects to the EDMs at two-loop order. The high sensitivity of EDMs to CP-violating ALP interactions is emphasized exploiting both the current and projected experimental sensitivities
Composite Higgs boson pair production at the LHC
No full textThe measurement of the trilinear and quartic Higgs self-couplings is necessary for the reconstruction of the Higgs potential. This way the Higgs mechanism as the origin of electroweak symmetry breaking can be tested. The couplings are accessible in multi- Higgs production processes at the LHC. In this paper we investigate the prospects of measuring the trilinear Higgs coupling in composite Higgs models. In these models, the Higgs boson emerges as a pseudo-Goldstone boson of a strongly interacting sector, and the Higgs potential is generated by loops of the Standard Model (SM) gauge bosons and fermions. The Higgs self-couplings are modified compared to the SM and controlled by the compositeness parameter ξ in addition to the Higgs boson mass. We construct areas of sensitivity to the trilinear Higgs coupling in the relevant parameter space for various final states. © SISSA 2011
Probing Higgs couplings to light quarks via Higgs pair production
Full text linkWe consider the potential of the Higgs boson pair production process to probe the light quark Yukawa couplings. We show within an effective theory description that the prospects of constraining enhanced first generation light quark Yukawa couplings in Higgs pair production are similar to other methods and channels, due to a coupling of two Higgs bosons to two fermions. Higgs pair production can hence also probe if the Higgs sector couples non-linearly to the light quark generations. For the second generation, we show that by employing charm tagging for the Higgs boson pair decaying to cc¯γγ, we can obtain similarly good prospects for measuring the charm Yukawa coupling as in other direct probes
Top quark mass effects in gg → ZZ at two loops and off-shell Higgs boson interference
Full text linkWe consider top-quark mass effects in the Higgs-interference contribution to Z-boson pair production in gluon fusion. While this production mechanism is formally of next-to-next-to leading order, its contribution is numerically important above the top threshold M²ZZ=44m²t. This region is essential to constrain the width of the Higgs boson, and good control over the top-quark mass dependence is crucial. We determine the form factors that are relevant for the interference contribution at two-loop order using a method based on a conformal mapping and Pade ́ approximants constructed from the expansions of the amplitude for large top mass and around the top threshold
Higgs probes of top quark contact interactions and their interplay with the Higgs self-coupling
Full text linkWe calculate the dominant contributions of third generation four-quark
operators to single-Higgs production and decay. They enter via loop corrections
to Higgs decays into gluons, photons and , and in Higgs production
via gluon fusion and in association with top quark pairs. We show that these
loop effects can, in some cases, lead to better constraints than those from
fits to top quark data. Finally, we investigate whether these four-fermion
operators can spoil the determination of the trilinear Higgs self-coupling from
fits to single-Higgs data.Comment: 36 pages, 11 figure
Vector-like bottom quarks in composite Higgs models
Full text linkLike many other models, Composite Higgs Models feature the existence of heavy vector-like quarks. Mixing effects between the Standard Model fields and the heavy states, which can be quite large in case of the top quark, imply deviations from the SM. In this work we investigate the possibility of heavy bottom partners. We show that they can have a significant impact on electroweak precision observables and the current Higgs results if there is a sizeable mixing with the bottom quark. We explicitly check that the constraints from the measurement of the CKM matrix element V tb are fulfilled, and we test the compatibility with the electroweak precision observables. In particular we evaluate the constraint from the Z coupling to left-handed bottom quarks. General formulae have been derived which include the effects of new bottom partners in the loop corrections to this coupling and which can be applied to other models with similar particle content. Furthermore, the constraints from direct searches for heavy states at the LHC and from the Higgs search results have been included in our analysis. The best agreement with all the considered constraints is achieved for medium to large compositeness of the left-handed top and bottom quarks. © 2014 The Author(s)
Reconstruction of top-quark mass effects in Higgs pair production and other gluon-fusion processes
Full text linkAbstract We propose a novel method for the treatment of top-quark mass effects in the production of H (∗), HH, HZ and ZZ final states in gluon fusion. We show that it is possible to reconstruct the full top-quark mass dependence of the virtual amplitudes from the corresponding large-m t expansion and the non-analytic part of the amplitude near the top-quark threshold ŝ = 4m t 2 with a Padé ansatz. The reliability of our method is clearly demonstrated by a comparison with the recent NLO result for Higgs pair production with full top-quark mass dependence
NLO QCD corrections to Higgs pair production including dimension-6 operators
Full text linkNew Physics that becomes relevant at some high scale Λ beyond the experimental reach, can be described in the effective theory approach by adding higher-dimensional operators to the Standard Model (SM) Lagrangian. In Higgs pair production through gluon fusion, which gives access to the trilinear Higgs self-coupling, this leads not only to modifications of the SM couplings but also induces novel couplings not present in the SM. For a proper prediction of the cross section, higher order QCD corrections that are important for this process, have to be taken into account. The various higher-dimensional contributions are affected differently by the QCD corrections. In this paper, we provide the next-to-leading order (NLO) QCD corrections to Higgs pair production including dimension-6 operators in the limit of large top quark masses. Depending on the dimension-6 coefficients entering the Lagrangian, the new operators affect the relative NLO QCD corrections by several per cent, while modifying the cross section by up to an order of magnitude. © 2015, The Author(s)
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