High Energy Physics - Phenomenology (hep-ph)

Abstract: We study the contribution of a heavy right-handed Majorana neutrino to neutrinoless double beta decay ($0\nu\beta\beta$) via four-fermion effective interactions of Nambu-Jona-Lasinio (NJL) type. In this physical scenario, the sterile neutrino contributes to the nuclear transition through gauge, contact, and mixed interactions. Using the lower limit on the half-life of $0\nu\beta\beta$ from the KamLAND-Zen experiment, we then constrain the effective right-handed coupling between the sterile neutrino and the $W$ boson: $\mathcal{G}^{W}_{R}$. Eventually, we show that the obtained bounds are compatible with those found in the literature, which highlights the complementarity of this type of phenomenological study with high-energy experiments.

Abstract: Dynamical theories of dark energy predict new degrees of freedom with particular environmental sensitivity to avoid constraints on fifth forces. We show that the similar, yet complementary multi-purpose detector setup of the ATLAS and CMS experiments provides a unique opportunity to place sensitivity on such scenarios in a narrow, yet relevant parameter range. Furthermore, our investigation gives rise to a novel phenomenological signature that the LHC experiments can pursue to exploit their complementary detector design from a BSM perspective.

Abstract: The hard-scatter processes in hadronic collisions are often largely contaminated with soft background coming from pileup in proton-proton collisions, or underlying event in heavy-ion collisions. There are multiple methods to remove the effect of pileup for jets. Two such methods, Area Subtraction and Constituent Subtraction, use the pileup density as the main ingredient to estimate the magnitude of pileup contribution on an event-by-event basis. The state-of-the-art approaches to estimating pileup density are sensitive to the number of hard-scatter jets in the event. This paper presents a new pileup-density estimation method that minimizes the sensitivity on the presence of hard-scatter jets in the event. Using a detector-level simulation, we provide a comparison of the new method with the state-of-the-art estimation methods. We observe a significantly lower bias for the estimated pileup density when using the new method. We conclude that the new method has the potential to significantly improve pileup mitigation in proton-proton collisions or the underlying event subtraction in heavy-ion collisions.

Abstract: We provide updated predictions of the lifetimes of singly charmed baryons and mesons within the heavy quark expansion, with all known corrections included. A special attention is devoted to the choice of the charm mass and wavefunctions of heavy baryons. Our results accommodate the experimentally-favoured hierarchy of singly charmed baryon lifetimes \begin{eqnarray*} \tau(\Xi_c^0) < \tau(\Lambda_c^+)< \tau(\Omega_c^0) < \tau(\Xi_c^+)\, \end{eqnarray*} in contrast to earlier theoretical findings. Predictions for charmed meson lifetimes and semileptonic branching ratios are also in agreement, within uncertainties, with a recent comprehensive study and with experimental results.

Abstract: In this short talk, we present a renormalizable model that can i) generate neutrino masses via a low-scale seesaw mechanism and ii) solve the long-standing $(g-2)_\mu$ and the more recent CDF II $M_W$-anomalies. This is minimally achieved by introducing two sterile neutrinos and a single electroweak-doublet vector-like lepton, with masses $< 2$ TeV. We focus on the one-generation scenario and the requirements to extend it to three generations.

Abstract: A variety of supergravity and string models involve hidden sectors where the hidden sectors may couple feebly with the visible sectors via a variety of portals. While the coupling of the hidden sector to the visible sector is feeble its coupling to the inflaton is largely unknown. It could couple feebly or with the same strength as the visible sector which would result in either a cold or a hot hidden sector at the end of reheating. These two possibilities could lead to significantly different outcomes for observables. We investigate the thermal evolution of the two sectors in a cosmologically consistent hidden sector dark matter model where the hidden sector and the visible sector are thermally coupled and their thermal evolution occurs without the assumption of separate entropy conservation for each sector. Within this framework we analyze several phenomena to illustrate their dependence on the initial conditions. These include the allowed parameter space of models, dark matter relic density, proton-dark matter cross section, effective massless neutrino species at BBN time, self-interacting dark matter cross-section, where self-interaction occurs via exchange of dark photon, and Sommerfeld enhancement. Finally fits to the velocity dependence of dark matter cross sections from galaxy scales to the scale of galaxy clusters is given. The analysis indicates significant effects of the initial conditions on the observables listed above. The analysis is carried out within the framework where dark matter is constituted of dark fermions and the mediation between the visible and the hidden sector occurs via the exchange of dark photons. The techniques discussed here may have applications for a wider class of hidden sector models using different mediations between the visible and the hidden sectors to explore the impact of Big Bang initial conditions on observable physics.