arXiv subjects

Neetu Raj Singh Chundawat

Publications and source records attributed to Neetu Raj Singh Chundawat.

24 records · Page 2Linked to original sources

arXiv2023

Cosmic neutrino flux and spin flavor oscillations in intergalactic medium

The ultra high energy (UHE) cosmic neutrinos are expected to play a pivotal role in the disquisition of physics beyond the standard model of particle physics as well as serve as an ideal cosmic messengers. This epitomizes the selling point of several currently running or planned neutrino telescopes. The UHE cosmic neutrinos usually perambulate gargantuan scales in the extragalactic universe having a magnetic field. If neutrinos have a finite magnetic moment ($μ_ν$) owing to quantum loop corrections, this may result in spin-flavor oscillations, which can affect the cosmic neutrino flux. Using the current limit and assuming neutrinos to be Dirac particles, we show that the flux of cosmic neutrinos will reduce by half if they traverse few Mpcs through the intergalactic magnetic field, in the range of $\rm μG$ to $nG$. Moreover, one can safely neglect the effect of $μ_ν$ if the current upper bound is improved by a few orders of magnitude even if the neutrinos travel through the size of the visible universe.

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arXiv2023

New physics in $B \to K^* τ^+ τ^-$: A model independent analysis

In this work we consider the implications of current $b \to s \ell^+ \ell^-$ ($\ell=e,\,μ$) measurements on several $B \to K^* τ^+ τ^-$ observables under the assumption that the possible new physics can have both universal as well as nonuniversal couplings to leptons. For new physics solutions which provide a good fit to all $b \to s \ell^+ \ell^-$ data, we intend to identify observables with large deviations from the Standard Model (SM) predictions as well as to discriminate between various new physics solutions. For this we consider the $B \to K^* τ^+ τ^-$ branching fraction, the $K^*$ longitudinal fraction $f_L$, the tau forward-backward asymmetry $A_{FB}$ and the optimized observables in the $P_i^{(')}$ basis. Further, we construct the $τ- μ$ lepton-flavor differences ($Q^{τμ}$) between these tau observables and their muonic counterparts in $B \to K^* μ^+ μ^-$ decay. Moreover, we also consider lepton-flavor ratios ($R^{τμ}$) of all of these observables. We find that the current data allows for deviations ranging from 25% up to an order of magnitude from the SM value in a number of observables. For e.g., the magnitudes of $Q^{τμ}_{P_3}$ and $Q^{τμ}_{P'_8}$ observables can be enhanced up to an order of magnitude, a twofold enhancement in $Q^{τμ}_{A_{FB}}$ is possible along with $\sim$50% enhancement in $R^{τμ}_{K^*}$ and $\sim$25% in $R^{τμ}_{A_{FB}}$. Moreover, the branching ratio of $B \to K^* τ^+ τ^-$ can be suppressed up to 25%. A precise measurement of these observables can also discriminate between a number of new physics solutions.

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arXiv2022

A global analysis of $b \to s \ell \ell$ data in heavy and light $Z'$ models

We perform a model-independent global fit to all $b \to s \ell \ell$ data in the light of recent measurements of the lepton flavour universality violating (LFUV) observables $R_{K_S^0}$ and $R_{K^{*+}}$ as well as the updated measurements of observables in $B_s \to ϕμ^+ μ^-$ decay, by the LHCb collaboration. We obtain new physics (NP) solutions to the current anomalies in the data, assuming NP in the muon sector only. We find that the 1D NP scenarios $C_9^{\rm NP} <0 $ and $C_{9}^{\rm NP}=-C_{10}^{\rm NP}$ continue to be the most favoured ones. However, the significance of the then favoured scenario $C_{9}^{\rm NP}=-C'_{9}$ has reduced and the updated data now marginally prefers $C_{10}^{\rm NP}$ scenario over $C_{9}^{\rm NP}=-C'_{9}$. The 2D scenarios $(C_9^{\rm NP}, C_{10}^{\prime} )$, $(C_9^{\rm NP}, C_{9}^{\prime} )$ and $(C_9^{\rm NP}, C_{10}^{\rm NP} )$, continue to be favoured by the data in the listed order. We also analyse generic TeV scale $Z'$ models which can generate the favored 1D scenarios, $C_9^{\rm NP} $ and $C_9^{\rm NP} = -C_{10}^{\rm NP}$ along with the 2D NP scenarios $(C_9^{\rm NP}, C_{9}^{\prime} )$ and $(C_9^{\rm NP}, C_{10}^{\rm NP} )$. Using the additional constraints from $B_s -\bar{B_s}$ mixing and neutrino trident data, we find that all four models provide an equally good fit to the data. Further, we consider a model with a 25 MeV $Z'$ that couples to muons and has a $q^2$ dependent $b - s$ coupling. We also study the implications of the current data on the LFUV observable $R_ϕ$, $Q_{4,5}$ along with $R_{K^{(*)}}$ in the high $q^2$. We find that a precise measurements of these observables can provide a good discrimination between a few favored model-independent solutions, and have a potential to disentangle different heavy and light $Z'$ scenarios considered in this work.

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arXiv2022

UHE neutrinos encountering decaying and non-decaying magnetic fields of compact stars

The phenomena of neutrino spin flavour precession in the presence of an extraneous magnetic field is a repercussion of neutrino magnetic moment which is consociated with the physics beyond the standard model of electroweak interactions. Ultra high energy neutrinos are spawned from a number of sources in the universe including the highly energetic astrophysical objects such as active galactic nuclei, blazar or supermassive black holes. When such high energy neutrinos pass through any compact stellar objects like neutron stars or white dwarfs, their flux can significantly reduce due to the exorbitant magnetic field provided by these compact objects. For Dirac neutrinos, such phenomena occur due to the conversion of neutrinos to their sterile counterparts. In this work, we consider a neutron star possessing a spatially varying magnetic field which may or may not decay with time. We find that, for the non-decaying magnetic field, the flux of high energy Dirac neutrinos becomes nearly half after passing through the neutron star. The flux is further enfeebled by $\sim 10\%$ in the presence of muons inside the neutron star. For decaying magnetic field, the flux reduction is abated by $\sim 5\%$ as compared to the temporally static magnetic field. In the case of a white dwarf, the depletion of flux is lesser as compared to the neutron stars.

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arXiv2022

Can neutron star discriminate between Dirac and Majorana neutrinos?

Any observable repercussion of electromagnetic properties of neutrinos will provide a perspicuous signature of new physics. This includes the phenomenon of neutrino spin flip in the propinquity of an external magnetic field. In this work, we study the inklings of spin flip in a neutron star with a radially varying magnetic field and matter density, known as a magnetar, which is also a source of profuse production of neutrinos during its initial stage of thermal evolution. We find that a precise measurement of neutrino flux emerging from a neutron star would reeducate discrimination between Dirac and Majorana neutrinos as the flux reduction due to spin flip oscillations are different for both types of neutrinos. Further, the reduction of flux is more preeminent near the surface as compared to the core of a neutron star.

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arXiv2022

Impact of $b \to s \ell \ell$ anomalies on rare charm decays in non-universal $Z'$ models

In this work, we study the impact of $b \to s \ell \ell$, $B_s - \bar{B_s}$ mixing and neutrino trident measurements on observables in decays induced by $c \to u $ transition in the context of a non-universal $Z'$ model which generates $C^{\rm NP}_{9} <0$ and $C^{\rm NP}_9 = - \,C^{\rm NP}_{10} $ new physics scenarios at the tree level. We inspect the effects on $D^0 \to π^0 ν\barν$, $D^+ \to π^+ ν\barν$ and $B_c \to B^+ ν\barν $ decays which are induced by the quark level transition $c \to u ν\barν$. The fact that the branching ratios of these decays are negligible in the standard model (SM) and the long distance effects are relatively smaller in comparison to their charged dileptons counterparts, they are considered to provide genuine null-tests of SM. Therefore the observation of these modes at the level of current as well as planned experimental sensitivities would imply unambiguous signature of new physics. Using the constraints on $Z'$ couplings coming from a combined fit to $b \to s \ell \ell$, $ΔM_s$ and neutrino trident data, we find that any meaningful enhancement over the SM value is ruled out in the considered framework. The same is true for $D - \bar{D}$ mixing observable $ΔM_D$ along with $D^0 \to μ^+ μ^-$ and $D^+ \to π^+ μ^+ μ^-$ decay modes which are induced through $c \to u μ^+ μ^-$ transition.

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