Diphoton Resonances at the LHC

We review the current status of searches for new physics beyond the Standard Model in the diphoton channel at the LHC and estimate the reach with future collected data. We perform a model independent analysis based on an effective field theory approach and different production mechanisms. As an illustrative example, we apply our results to a scenario of minimal composite dynamics.Comment: 13 pages, 3 figures; invited review for MPLA; journal versio

Potential for probing three-body decays of Long-Lived Particles with MATHUSLA

Several extensions of the Standard Model predict the existence of Long-Lived Neutral Particles (LLNPs) with masses in the multi-GeV range and decay lengths of O(100 m) or longer. These particles could be copiously produced at the LHC, but the decay products cannot be detected with the ATLAS or CMS detectors. MATHUSLA is a proposed large-volume surface detector installed near ATLAS or CMS aimed to probe scenarios with LLNPs which offers good prospects for disentangling the physics underlying two-body decays into visible particles. In this work we focus on LLNP decays into three particles with one of them being invisible, which are relevant for scenarios with low scale supersymmetry breaking, feebly interacting dark matter or sterile neutrinos, among others. We analyze the MATHUSLA prospects to discriminate between two- and three-body LLNP decays, as well as the prospects for reconstructing the underlying model parameters.Comment: 11 pages, 4 figures, matches journal versio

CP Violation in the Lepton Sector, Thermal Leptogenesis and Lepton Flavour Violating Processes

It is a well established experimental fact that the Universe is strongly asymmetric in its matter and antimatter content. Indeed, there is no direct/indirect evidence up to now about the formation of primordial stars or galaxies made entirely of antiparticles. The only clear observation of antimatter in the Universe, besides the one created in particle accelerators, resides on the measurement of the cosmic ray flux through the Earth....

Collider Tests of (Composite) Diphoton Resonances

We analyze the Large Hadron Collider sensitivity to new pseudoscalar resonances decaying into diphoton with masses up to scales of few TeVs. We focus on minimal scenarios where the production mechanisms involve either photon or top-mediated gluon fusion, partially motivated by the tantalizing excess around 750 GeV reported by ATLAS and CMS. The two scenarios lead respectively to a narrow and a wide resonance. We first provide a model-independent analysis via effective operators and then introduce minimal models of composite dynamics where the diphoton channel is characterized by their topological sector. The relevant state here is the pseudoscalar associated with the axial anomaly of the new composite dynamics. If the Standard Model top mass is generated via four-fermion operators the coupling of this state to the top remarkably explains the wide-width resonance reported by ATLAS. Beyond the excess, our analysis paves the way to test dynamical electroweak symmetry breaking via topological sectors.Comment: 17 pages, 5 figure

Minimal Composite Dynamics versus Axion Origin of the Diphoton excess

ATLAS and CMS observe deviations from the expected background in the diphoton invariant mass searches of new resonances around 750 GeV. We show that a simple realization in terms of a new pseudoscalar state can accommodate the observations. The model leads to further footprints that can be soon observed. The new state can be interpreted both as an axion or as a {highly natural} composite state arising from minimal models of dynamical electroweak symmetry breaking. We further show how to disentangle the two scenarios. Beyond the possible explanation of the diphoton excess the results show that it is possible to directly test and constrain composite dynamics via processes stemming from its distinctive topological sector.Comment: 6 pages, Latex. Improved version with new figures and further detail