Setting limits on Effective Field Theories: the case of Dark Matter

The usage of Effective Field Theories (EFT) for LHC new physics searches is receiving increasing attention. It is thus important to clarify all the aspects related with the applicability of the EFT formalism in the LHC environment, where the large available energy can produce reactions that overcome the maximal range of validity, i.e. the cutoff, of the theory. We show that this does forbid to set rigorous limits on the EFT parameter space through a modified version of the ordinary binned likelihood hypothesis test, which we design and validate. Our limit-setting strategy can be carried on in its full-fledged form by the LHC experimental collaborations, or performed externally to the collaborations, through the Simplified Likelihood approach, by relying on certain approximations. We apply it to the recent CMS mono-jet analysis and derive limits on a Dark Matter (DM) EFT model. DM is selected as a case study because the limited reach on the DM production EFT Wilson coefficient and the structure of the theory suggests that the cutoff might be dangerously low, well within the LHC reach. However our strategy can also be applied to EFT's parametrising the indirect effects of heavy new physics in the Electroweak and Higgs sectors

Optimal Bounds on Heavy-Mediator Dark Matter

The aim of the thesis is to design a model-indepedent strategy for the interpretation of Dark Matter searches at colliders, using as reference the CMS mono-jet analysis of the data gathered by the detector in 2015. The strategy is based on the consistent usage of the Effective Field Theory (EFT) description of the Dark Matter signal that allows us to set bounds under the hypothesis that the Dark Matter interactions are due to the exchange of heavy mediator particles. Implementing it in a concrete experimental situations and assessing the expected limits requires a detailed study of the background and a refined simulation of the signal. Moreover, a new statistical procedure, based on the Shape Analysis method, is introduced in order to set universal bounds on heavy-mediator Dark Matter production at LHC. A comparison is performed between the performances of the new statistical method and those of a more traditional cut and count strategy. EFT limits can be reinterpreted in any specific underlying model

Hiking the ALPs: Signatures and Models

In this thesis work some aspects of the Axion-Like Particles (ALP) physics are presented. After a didascalic introduction on QCD axions and, more generally, on ALPs, an innovative approach to search for such type of particles at B-factories is explained. In the second part of the work, a solution for an ALP or axion to rise in a composite Higgs model framework is described, including some phenomenological results

Hiking the ALPs: Signatures and Models

In this thesis work some aspects of the Axion-Like Particles (ALP) physics are presented. After a didascalic introduction on QCD axions and, more generally, on ALPs, an innovative approach to search for such type of particles at B-factories is explained. In the second part of the work, a solution for an ALP or axion to rise in a composite Higgs model framework is described, including some phenomenological results

Leptoquarks and real singlets: A richer scalar sector behind the origin of dark matter

We investigate scenarios with O(1  TeV) scalar leptoquarks that act as portals between the Standard Model and dark matter. We assume that dark matter is a scalar singlet S which couples to a scalar leptoquark Δ and the Higgs boson via the terms in the scalar potential. In addition, the leptoquark is endowed with Yukawa couplings to quarks and leptons that may address the anomalies in B meson decays. We consider the SS annihilation cross sections to estimate the dark matter relic abundance and explore the interplay between astrophysical, collider, and flavor physics bounds on such models. In the heavy dark matter window, mS>mΔ, the leptoquark portal becomes the dominant mechanism to explain the dark matter abundance. We find that the leptoquark Yukawa couplings, relevant for quark and lepton flavor physics, are decoupled from the dark matter phenomenology. By focussing on a scenario with a single leptoquark state, we find that relic density can only be explained when both Δ and S masses are lighter than O(10  TeV)

Leptoquarks and real singlets: A richer scalar sector behind the origin of dark matter

none5We investigate scenarios with scalar leptoquarks that act as portals between the Standard Model and dark matter. We assume that dark matter is a scalar singlet which couples to a scalar leptoquark and the Higgs boson via the terms in the scalar potential. In addition, the leptoquark is endowed with Yukawa couplings to quarks and leptons that may address the anomalies in meson decays. We consider the annihilation cross sections to estimate the dark matter relic abundance and explore the interplay between astrophysical, collider, and flavor physics bounds on such models. In the heavy dark matter window, , the leptoquark portal becomes the dominant mechanism to explain the dark matter abundance. We find that the leptoquark Yukawa couplings, relevant for quark and lepton flavor physics, are decoupled from the dark matter phenomenology. By focussing on a scenario with a single leptoquark state, we find that relic density can only be explained when both and masses are lighter than .noneD'Eramo F.; Kosnik N.; Pobbe F.; Smolkovic A.; Sumensari O.D'Eramo, F.; Kosnik, N.; Pobbe, F.; Smolkovic, A.; Sumensari, O