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### Browsing Theses by Supervisor "Alok, Ashutosh Kumar"

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Item Probing New Physics Through Bottom and Top Quark Decays.(Indian Institute of Technology Jodhpur, 2020-10) Alok, Ashutosh KumarShow more There are several measurements in the decays of B mesons which show discrepancy with the predictions of the Standard Model (SM) of electro-weak interactions. Many such measurements are in the decays induced by the quark level transition b ! s l+ l (l = e; ). In order to discriminate between various new physics solutions and pin down the type of new physics responsible for anomalies in b ! s l+ l transition, one should look for alternative observables. The purely leptonic decay of B s meson is considered to be a golden channel to probe beyond SM Physics in b ! s l+ l sector as it is theoretically very clean. Assuming new physics only in b ! s + , we perform a model independent analysis of new physics in B s ! + decay to identify operator(s) which can provide large enhancement in the branching ratio of B s ! + above its SM value. We find that a significant enhancement in Br(B s ! + ) is not allowed by any of the allowed solutions. In fact, the present b ! s + data indicates that the future measurements of Br(B s ! + ) is expected to be suppressed in comparison to the SM. We then consider a new observable, the longitudinal polarization asymmetry of muons in B s ! + decay. We find that this observable is a good discriminant between the new physics solutions if it can be measured to a precision of 10%. We also investigate the potential impact of b ! c anomalies on B s ! + decay in a model where the new physics contributions to these two transitions are strongly correlated. We find that the branching ratio of B s ! + can be enhanced by three orders of magnitude. We then consider new physics only in b ! s e+ e decay. Including all measurements in b ! se+e sector along with lepton-universality violating ratios RK( ) , we perform a model independent analysis of new physics by considering effective operators in the form of vector/axial-vector (V/A), scalar/pseudoscalar (S/P) and tensors (T). We find that S/P operators cannot account for the anomalous measurements of RK( ) due to tight constraints coming from the upper bound on the branching ratio of Bs ! e+e. On the other hand, various V/A scenarios can alleviate the tension between RK( ) data and the SM predictions. This includes generating values for RK within 1 of its measured values in the low-q2 bin (0:045 GeV2 q2 1:1 GeV2). Further, we identify angular observables in B ! K e+e which can discriminate between the allowed V/A solutions. Moreover, it was previously shown that various combinations of V/A and T new physics operators can also explain RK( ) measurements. We find that K longitudinal polarization fraction, FL, in B ! K e+e decay can discriminate against pure V/A and (V/A+T) scenarios. A measurement of FL in (1 6) GeV2 bin with an absolute uncertainty of 0.05 can either confirm or rule out any combination of V/A and T new physics scenarios by more than 2 . Finally, we study the impact of B anomalies on rare top quark decay t ! cZ. Top quarks are particularly important for hunting new physics as it is the heaviest of all the SM particles. In particular, the flavour changing neutral current top quark decay t ! cZ has immense potential to probe new physics as it is highly suppressed in the SM. The SM prediction for its branching ratios is 1014 and is probably immeasurable at the LHC until new physics enhances its branching ratio up to the current detection level which is 104-105. Using relevant constraints from the B and K sectors, we show that the anomalous tcZ couplings can enhance the branching ratio of t ! cZ at the level of 104 provided the couplings are complex.Show more Item A Study of Quantum Mechanical Aspects in Neutrino Oscillations(Indian Institute of Technology Jodhpur, 2020-10) Alok, Ashutosh KumarShow more The phenomena of entanglement and the nonlocal features of quantum correlations were initially introduced to elegantly abase the opponents of quantum mechanics. However, owing to the development of the quantum information science, these quantum mechanical features have to be reassessed and to be elevated as resources that may be exploited to achieve tasks that are not possible within the realm of classical physics. Along these lines, quantum resource theories provide the framework to study and quantify these quantum effects, develop new protocols for its detection, and identify processes that optimize its use for a given application. Due to weakly interacting nature, the system of oscillating neutrinos can maintain quantum coherence over a long distance, which can be detected in long baseline experiments. Hence, neutrinos can prove to be promising candidates for various quantum information tasks. Also, the correlation measures used in our analysis can reveal important information about several open problems present in the neutrino sector, which makes this a dual study, important for both neutrino physics and quantum information theory. We study various facets of nonclassicality, quantified by spatial quantum correlations such as flavour entropy, geometric entanglement, Mermin and Svetlichny inequalities, in the system of three flavour neutrino oscillations in the context of ongoing accelerator neutrino experiments NOνA and T2K and upcoming experiment DUNE.We find that various witnesses show sensitivity to the mass-hierarchy problem and CP violation in neutrino physics. In order to test the efficiency and feasibility of neutrinos for QIP tasks, we also incorporated effects of new physics. For this study, we have chosen a measure of quantum coherence, the characteristic element of quantum mechanics which enfolds the defining features of the theory. The new physics effects are incorporated in a model-independent way within the framework of effective field theory, where higher dimensional operators (dimension-6) are added to the Standard Model (SM) Lagrangian. We show that the SM interaction provides favourable conditions for quantum information tasks for normal mass ordering, whereas new physics favours inverted ordering for such tasks. Also, we investigated the variation of coherence and mixedness encapsulated in the neutrino-system under the action of quantum decoherence. It is also interesting to see the features of quantum correlations in the effect of gravitational Zeeman-splitting, causing neutrino-antineutrino oscillations. Another interesting quantum mechanical phenomena, the geometric phase has been studied in neutrino system in the context of experiments T2K, NOνA and reactor neutrino experiments such as Daya Bay and RENO. It is seen that for neutrino experimental facilities where the geometric phase can complete one cycle, all the phase curves corresponding to different values of CP violating phase, converge to a single point, called the cluster point. There are two distinct cluster points for positive and negative signs of Δ31 (large mass-squared difference). Thus the geometric phase can contribute to our understanding of the neutrino mass hierarchy problem.Show more