在大額外維度的背景下探索一些粒子物理異常

Abstract

noneIn this dissertation, we probe three different anomalies in particle physics in the context of large extra dimensions (LEDs). The first anomaly refers to the lepton flavor universality violation (LFUV) found in b → sl+l− transition. Recently, the measurement of RK by LHCb supports the deviation on standard model (SM) predictions. The updated global fit preferred the muon Wilson coefficients to be Cbsμμ 9 = −Cbsμμ 10 = −0.41. Regarding this, we show that the contributions of all Kaluza-Klein (KK) modes of Dirac singlet neutrino propagating in the large extra dimensions explain the anomaly by naturally providing Cbsll9 = −Cbsll10. In particular, the muon Yukawa coupling strength hμ = 5 and two extra spatial dimensions suggest that the fundamental scale MF of the extra dimensions must be reduced to around 20 TeV. The second anomaly is about the anomalous values of RD(∗) . Recent measurements of RD(∗) by LHCb determine a significant discrepancy from its SM predictions. These values are associated with semi-leptonic B meson decays fueled by b → cτ ¯ν transition. The anomaly signals a new physics (NP) beyond the SM by violating lepton flavor universality. In our work, we show that the cumulative effects of the KK modes of right-handed singlet neutrino propagating in the large extra dimensions provide an explanation of the anomaly. As a result, the number of extra dimensions must be two to address RD(∗) . The fitting of the fundamental scale MF corresponds to the experimental values of RD and RD∗ , and it is in good agreement with experimental bounds from the lepton flavor violation in τ decays. However, the most stringent constraints from the neutrino experiments set new lower limits of MF , which are in tension to our findings. Therefore, if the central values of RD(∗) remain with smaller uncertainties using the future data, then the extra-dimensional framework with right-handed neutrinos propagating in the bulk will be excluded. Lastly, we address the puzzling Gamma Ray Burst GRB221009A event. In particular, the LHAASO and Carpet- 2 collaboration detected very energetic photons up to maximum energies of 18 TeV and 251 TeV, respectively. Observing such photons from a vast distance remains a mystery due to the severe attenuation from the extra background light (EBL) before the photons arrive on Earth. A possible remedy is the existence of axion-like particles (ALPs). The flux of very energetic photons from a host galaxy is converted into ALPS that travel intergalactically, unhindered by the EBL. In our third paper, we explore the effect of extra dimensions on the conversion probability of photons into ALPs. The conversion probability of very energetic photons may reach almost 100% and will saturate eventually. We show that the energies where the saturation occurs are affected by the size of the extra dimensions. Consequently, smaller extra dimensions are favored for detecting very energetic photons.