No abstract

Using the upper bound on the inelastic reaction cross-section implied by S-matrix unitarity, we derive the thermally averaged maximum dark matter (DM) annihilation rate for general k → 2 number-changing reactions, with k ≥ 2, taking place either entirely within the dark sector, or involving standard model fields. This translates to a maximum mass of the particle saturating the observed DM abundance, which, for dominantly s-wave annihilations, is obtained to be around 130 TeV, 1 GeV, 7 MeV and 110 keV, for k = 2, 3, 4 and 5, respectively, in a radiation dominated Universe, for a real or complex scalar DM stabilized by a minimal symmetry. For modified thermal histories in the pre-big bang nucleosynthesis era, with an intermediate period of matter domination, values of reheating temperature higher than $$ \mathcal{O}(200) $$ O 200 GeV for k ≥ 4, $$ \mathcal{O}(1) $$ O 1 TeV for k = 3 and $$ \mathcal{O}(50) $$ O 50 TeV for k = 2 are strongly disfavoured by the combined requirements of unitarity and DM relic abundance, for DM freeze-out before reheating.

We examine the phenomenology of the production, at the 13 TeV Large Hadron Collider (LHC), of a heavy resonance X , which decays via other new on-shell particles n into multi-(i.e. three or more) photon final states. In the limit that n has a much smaller mass than X , the multi-photon final state may dominantly appear as a two-photon final state because the γ s from the n decay are highly collinear and remain unresolved. We discuss how to discriminate this scenario from X → γ γ : rather than discarding non-isolated photons, it is better to relax the isolation criteria and instead form photon jets substructure variables. The spins of X and n leave their imprint upon the distribution of pseudo-rapidity gap η between the apparent two-photon states. Depending on the total integrated luminosity, this can be used in many cases to claim discrimination between the possible spin choices of X and n, although the case where X and n are both scalar particles cannot be discriminated from the direct X → γ γ decay in this manner. Information on the mass of n can be gained by considering the mass of each photon jet.

We identify a class of U(1) X models which can explain the R K anomaly and the neutrino mixing pattern, by using a bottom-up approach. The different X-charges of lepton generations account for the lepton universality violation required to explain R K . In addition to the three right-handed neutrinos needed for the Type-I seesaw mechanism, these minimal models only introduce an additional doublet Higgs and a singlet scalar. While the former helps in reproducing the quark mixing structure, the latter gives masses to neutrinos and the new gauge boson Z . Our bottom-up approach determines the Xcharges of all particles using theoretical consistency and experimental constraints. We find the parameter space allowed by the constraints from neutral meson mixing, rare b → s decays and direct collider searches for Z . Such a Z may be observable at the ongoing run of the Large Hadron Collider with a few hundred fb −1 of integrated luminosity.

We present a comprehensive analysis of observing a light Higgs boson in the mass range 70-110 GeV at the 13=14 TeV LHC, in the context of the type-I two-Higgs-doublet model. The decay of the light Higgs to a pair of bottom quarks is dominant in most parts of the parameter space, except in the fermiophobic limit. Here its decay to bosons (mainly a pair of photons) becomes important. We perform an extensive collider analysis for the bb and γγ final states. The light scalar is tagged in the highly boosted regimes for the bb mode to reduce the enormous QCD background. This decay can be observed with a few thousand fb −1 of integrated luminosity at the LHC. Near the fermiophobic limit, the decay of the light Higgs to a pair of photons can even be probed with a few hundred fb −1 of integrated luminosity at the LHC.