Alok, Ashtosh Kumar

Neutrinos may possess tiny magnetic moments (μν) via quantum corrections, by virtue of which they can undergo spin-flavor oscillations. This phenomenon can alter the flux of cosmic neutrinos. Considering the current limit on μν , we show that the flux of cosmic neutrinos will reduce by half if they traverse a few Mpcs through the intergalactic magnetic field, in the range of μG to nG. Furthermore, if the current upper bound is improved by a few orders of magnitude, the effect of μν can be safely neglected, even if the neutrinos travel through the size of the visible universe.

We investigate the potential of the ratios in ll and *ll decays (l =, ) to probe new physics in the - sector. We find that this ratio deviates from their SM prediction even for universal couplings. This implies that the bare deviation of these ratios from their SM predictions cannot confirm the nature of possible new physics. For this, we need to compare the allowed range of for a class of solutions with only universal couplings to leptons and solutions having both universal and non-universal components. By comparing the predictions of and * for the two class of solutions using the current data, we find that the solutions with only universal couplings and solutions having both universal and non-universal couplings can be discriminated if the measured value of is greater than the SM prediction.

In recent times several signatures of beyond standard model (SM) physics have appeared in a number of observables related to the semi-leptonic decays of B mesons. Further, the magnetic moment of muon also shows deviation from SM at the level of 4σ. A number of proposed new physics models can accommodate these anomalies. A class of these models also contain dark matter (DM) candidates. We intend to distinguish between a Lμ − Lτ DM which is considered to reconcile the (g − 2)μ anomaly and a heavier muonphilic DM candidate which can also account for the B-anomalies. We find that one type of the DM compels the neutrinos to change the flavor ratios whereas for the other type of DM, the neutrinos mimic the flavor ratio of the vacuum. The DM-neutrino interaction, thus, has the potential to discriminate between flavor models with a dark connection.

The recent measurement of RK∗ is yet another hint of new physics (NP) and supports the idea that it is present in b → sμμ- decays. We perform a combined model-independent and model-dependent analysis in order to deduce properties of this NP. Like others, we find that the NP must obey one of two scenarios: (I) Cμμ 9 NP < 0 or (II) Cμμ 9 NP = -Cμμ 10 NP < 0. A third scenario, (III) Cμμ 9 NP = -C0μμ 9 NP, is rejected largely because it predicts RK = 1, in disagreement with experiment. The simplest NP models involve the tree-level exchange of a leptoquark (LQ) or a Z0 boson.We show that scenario II can arise in LQ or Z0 models, but scenario I is only possible with a Z0. Fits to Z0 models must take into account the additional constraints from B0s - B0s mixing and neutrino trident production. Although the LQs must be heavy, O(TeV), we find that the Z0 can be light, e.g., MZ0 = 10 GeV or 200 MeV.

The measurements of the ratios RK(∗) along with RD(∗) hint towards lepton flavor non universality which is in disagreement with the standard model. In this work, we reanalyze the four new physics models, which are widely studied in the literature as a candidates for the simultaneous explanations of these measurements. These are, standard model like vector boson (VB), SU(2) L-singlet vector leptoquark (U1), SU(2) L-triplet scalar leptoquark (S3) and SU(2) L triplet vector leptoquark (U3) models. We assume a coupling only to the third generation in the weak basis, so that the b→ sμ+μ- transition is generated only via mixing effects. Preforming a global fit to all relevant data, we show that the vector boson model violates the current upper bound on Br(τ→ 3 μ) and hence is inconsistent with the present data. Further, we show that within this framework, the U1 leptoquark model cannot simultaneously accommodate RK(∗) and RD(∗) measurements. We emphasize that this conclusion is independent of the additional constraints coming from renormaliztion group running effects and high-pT searches. In addition, we show that the S3 and U3 models are highly disfavored by the constraints coming from b→ sνν¯ data. Finally, we find a that hypothesis of two LQ particles is also challenged by b→ sν¯ ν data.

Many facets of nonclassicality are probed in the context of three flavour neutrino oscillations including matter effects and CP violation. The analysis is carried out for parameters relevant to two ongoing experiments NO νA and T2K, and also for the upcoming experiment DUNE. The various quantum correlations turn out to be sensitive to the mass-hierarchy problem in neutrinos. This sensitivity is found to be more prominent in DUNE experiment as compared to NO νA and T2K experiments. This can be attributed to the large baseline and high energy of the DUNE experiment. Further, we find that to probe these correlations, the neutrino (antineutrino) beam should be preferred if the sign of mass square difference Δ31 turns out to be positive (negative).

One of the exciting results in flavor physics in recent times is the RD/RD⁎ puzzle. The measurements of these flavor ratios performed by the B-factory experiments, BaBar and Belle, and the LHCb experiment are about 4σ away from the Standard Model expectation. These measurements indicate that the mechanism of b→cτν¯ decay is not identical to that of b→c(μ/e)ν¯. This charge lepton universality violation is particularly intriguing because these decays occur at tree level in the Standard Model. In particular, we expect a moderately large new physics contribution to b→cτν¯. The different types of new physics amplitudes, which can explain the RD/RD⁎ puzzle, have been identified previously. In this letter, we show that the polarization fractions of τ and D⁎ and the angular asymmetries AFB and ALT in B→D⁎τν¯ decay have the capability to uniquely identify the Lorentz structure of the new physics. A measurement of these four observables will lead to such an identification.

In this work we study temporal quantum correlations, quantified by Leggett-Garg (LG) and LG-type inequalities, in the B and K meson systems. We use the tools of open quantum systems to incorporate the effect of decoherence which is quantified by a single phenomenological parameter. The effect of CP violation is also included in our analysis. We find that the LG inequality is violated for both B and K meson systems, the violation being most prominent in the case of K mesons and least for Bs system. Since the systems with no coherence do not violate LGI, incorporating decoherence is expected to decrease the extent of violation of LGI and is clearly brought out in our results. We show that the expression for the LG functions depends upon an additional term, apart from the experimentally measurable meson transition probabilities. This term vanishes in the limit of zero decoherence. On the other hand, the LG-type parameter can be directly expressed in terms of transition probabilities, making it a more appropriate observable for studying temporal quantum correlations in neutral meson systems.

We study the geometric phase for neutrinos at various man-made facilities, such as the reactor and accelerator neutrino experiments. The analysis is done for the three flavor neutrino scenario, in the presence of matter and for general, noncyclic paths. The geometric phase is seen to be sensitive to the CP violating phase in the leptonic sector and the sign ambiguity in . We find 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. Thus, the geometric phase can contribute to our understanding of the neutrino mass hierarchy problem.

We study the impact of decoherence on B meson systems with specific emphasis on Bs. For consistency we also study the Bd mesons based on the most recent data. Even though the study of decoherence made here depends upon the basis chosen and the final decay products, our analysis suggests that the coherence property of B meson systems is robust and could be a good candidate for making a study of foundational aspects of quantum mechanics. © 2013 American Physical Society.