arXiv subjects

Sunando Kumar Patra

Publications and source records attributed to Sunando Kumar Patra.

33 records · Page 2Linked to original sources

arXiv2018

$b \to c τν_τ$ Decays: A Catalogue to Compare, Constrain, and Correlate New Physics Effects

In this article, we have predicted the standard model (SM) values of the asymmetric and angular observables in $B\to D^{(\ast)}τν_τ$ decays, using the results of the new up-to-date analysis in $B\to D^{(*)}\ellν_{\ell}$. We have also revisited the SM prediction of the inclusive ratio $\mathcal{R}_{X_c}$, and have given its values in different schemes of the charm quark mass. This is the first analysis which includes all the known corrections in the SM. In addition, we have analysed the $b\to cτν_τ$ decay modes in a model-independent framework of effective field theory beyond the standard model. Considering all the possible combinations of the effective operators in $b \to c τν_τ$ decays and using the Akaike Information Criterion, we find out the scenarios which can best explain the available data on these channels. In the selected scenarios, best-fit values and correlations of the new parameters are extracted. Using these results, predictions are made on various observables in the exclusive and inclusive semitaunic $b \to c $ decays. The graphical correlations between these observables are shown, which are found to be useful in discriminating various new physics scenarios.

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arXiv2018

CoDEx: Wilson coefficient calculator connecting SMEFT to UV theory

CoDEx is a Mathematica package that calculates the Wilson Coefficients (WCs) corresponding to effective operators up to mass dimension-6. Once the part of the Lagrangian involving single as well as multiple degenerate heavy fields, belonging to some Beyond Standard Model (BSM) theory, is given, the package can then integrate out propagators from the tree as well as 1-loop diagrams of that BSM theory. It then computes the associated WCs up to 1-loop level, for two different bases: "Warsaw" and "SILH". CoDEx requires only very basic information about the heavy field(s), e.g., Colour, Isospin, Hyper-charge, Mass, and Spin. The package first calculates the WCs at the high scale (mass of the heavy field(s)). We then have an option to perform the renormalisation group evolutions (RGEs) of these operators in "Warsaw" basis, a complete one (unlike "SILH"), using the anomalous dimension matrix. Thus, one can get all effective operators at the electro-weak scale, generated from any such BSM theory, containing heavy fields of spin: 0, 1/2, and 1. We have provided many example models (both here and in the package-documentation) that more or less encompass different choices of heavy fields and interactions. Relying on the status of the present day precision data, we restrict ourselves up to dimension-6 effective operators. This will be generalised for any dimensional operators in a later version. Site: https://effexteam.github.io/CoDEx

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arXiv2018

New physics with the lepton flavor violating decay $τ\to 3μ$

Lepton flavour violating (LFV) processes are a smoking gun signal of new physics (NP). If the semileptonic $B$ decay anomalies are indeed due to some NP, such operators can potentially lead to LFV decays involving the second and the third generation leptons, like $τ\to 3μ$. In this paper, we explore how far the nature of NP can be unraveled at the next generation $B$-factories like Belle-II, provided the decay $τ\to 3μ$ has been observed. We use four observables with which the differentiation among NP operators may be achieved to a high confidence level. Possible presence of multiple NP operators are also analysed with the Optimal Observable technique. While the analysis can be improved even further if the final state muon polarisations are measured, we present this work as a motivational tool for the experimentalists, as well as a template for the analysis of similar processes.

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arXiv2018

Roadmap of left-right models based on GUTs

We perform a detailed study of the grand unified theories $SO(10)$ and $E(6)$ with left-right intermediate gauge symmetries of the form $SU(N)_L\otimes SU(N)_R \otimes \mathcal{G}$. Proton decay lifetime constrains the unification scale to be $ \gtrsim 10^{16}$ GeV and, as discussed in this paper, unwanted cosmological relics can be evaded if the intermediate symmetry scale is $ \gtrsim 10^{12}$ GeV. With these conditions, we study the renormalization group evolution of the gauge couplings and do a comparative analysis of all possible left-right models where unification can occur. Both the D-parity conserved and broken scenarios, as well as the supersymmetric (SUSY) and Non-supersymmetric (Non-SUSY) versions, are considered. In addition to the fermion and scalar representations at each stage of the symmetry breaking, contributing to the $β$-functions, we list the intermediate left-right groups which successfully meet these requirements. We make use of the dimension-5 kinetic mixing effective operators for achieving unification and large intermediate scale. A significant result in the supersymmetric case is that to achieve successful unification for some breaking patterns, the scale of SUSY breaking needs to be at least a few TeV. In some of these cases, the intermediate scale can be as low as $\sim 10^{12}$ GeV, for SUSY scale to be $\sim 30$ TeV. This has important consequences in the collider searches for SUSY particles and phenomenology of the lightest neutralino as dark matter.

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arXiv2018

$\mathcal{R}(D^{(*)})$ anomalies in light of Non-Minimal Universal Extra Dimension

We estimate contributions from Kaluza-Klein excitations of gauge bosons and physical charge scalar for the explanation of the lepton flavor universality violating excess in the ratios $\mathcal{R}(D)$ and $\mathcal{R}(D^*)$ in 5 dimensional Universal Extra Dimensional scenario with non-vanishing boundary localized terms. This model is conventionally known as non-minimal Universal Extra Dimensional model. We obtain the allowed parameter space in accordance with constraints coming from $B_c \to τν$ decay, as well as those from the electroweak precision tests.

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arXiv2017

Non-Abelian Vector Boson Dark Matter, its Unified Route and signatures at the LHC

Vector boson dark matter (DM) appears in $SU(2)_N$ extension ($N$ stands for neutral) of Standard Model (SM) where an additional global $U(1)_P$ symmetry is assumed and results in a generalized lepton number defined as: $L=P+T_{3N}$. Breaking of $U(1)_P$ leads to the breaking of $L$ to $(-1)^L$, thus stabilizing DM through modified $R=(-1)^{3B+L+2J}$. This model, already discussed in literature, offers several novel features to elaborate upon. For example, $t$-channel annihilation and dominant $s$-channel direct search, along with co-annihilation, helps the DM to evade stringent direct search bounds from LUX and XENON1T after satisfying relic density constraints. On the other hand, the exotic particles of the model can be produced at the Large Hadron Collider (LHC) yielding multilepton final states. Hadronically quiet four lepton signal with large missing energy, in specific, is shown to provide a smoking gun signature of such a framework. We study the details of $E(6) \to SM \otimes SU(2)_N$ breaking patterns (through D-parity odd/even cases) which yield important phenomenological consequences.

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arXiv2017

Extraction of $|V_{cb}|$ from $B\to D^{()}\ellν_\ell$ and the Standard Model predictions of $R(D^{()})$

We extract $|V_{cb}|$ from the available data in the decay $B \to D^{(*)}\ellν_{\ell}$. Our analysis uses the $q^2(w)$ binned differential decay rates in different subsamples of $B\to D\ellν_\ell$ ($\ell = e, μ$), while for the decay $B\to D^*\ellν_\ell$, the unfolded binned differential decay rates of four kinematic variables including the $q^2$ bins have been used. In the CLN and BGL parameterizations of the form factors, the combined fit to all the available data along with their correlations yields $|V_{cb}| = (39.77 \pm 0.89)\times 10^{-3}$ and $(40.90 \pm 0.94)\times 10^{-3}$ respectively. In these fits, we have used the inputs from lattice and light cone sum rule (LCSR) along with the data. Using our fit results and the HQET relations (with the known corrections included) amongst the form factors, and parameterizing the unknown higher order corrections (in the ratios of HQET form factors) with a conservative estimate of the normalizing parameters, we obtain $R(D^{*}) = 0.259 \pm 0.006$ (CLN) and $R(D^*) = 0.257 \pm 0.005$ (BGL).

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arXiv2017

Optimal observable analysis for the decay $b \to s$ plus missing energy

The decay $b\to sν\barν$ has been a neglected sibling of $b\to s\ell^+\ell^-$ because neutrinos pass undetected and hence the process offers less number of observables. We show how the decay $b\to s~+$~invisible(s) can shed light, even with a limited number of observables, on possible new physics beyond the Standard Model and also show, quantitatively, the reach of future $B$ factories like SuperBelle to uncover such new physics. Depending on the operator structure of new physics, different channels may act as the best possible probe. We show, using the Optimal Observable technique, how almost the entire parameter space allowed till now can successfully be probed at a high luminosity $B$ factory.

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arXiv2017

Unified resolution of the $R(D)$ and $R(D^*)$ anomalies and the lepton flavor violating decay $h\toμτ$

Taking advantage of the fact that the flavor of the neutrino in semileptonic $B$ decays $B\to D^{(*)}τν$ is not known, we show how a minimal set of higher-dimensional lepton flavor violating (LFV) operators can explain the $R(D^{(*)})$ anomalies, and as a spin-off, can give rise to the LFV decay of the Higgs boson, $h\toμτ$. We also show how none but the minimal set of operators survive the present data.

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arXiv2016

Optimal-observable analysis of possible new physics in $B\to D^{(\ast)}τν_τ$

We study all possible observables in $B\to D^{(\ast)}τν_τ$ with new physics (NP), including new vector, scalar and tensor interactions, and investigate the prospects of extracting NP Wilson coefficients with optimal observables. Analysis of the full $q^2$ integrated branching fractions of $B\to D^{(\ast)}τν_τ$ show that the overall sensitivity of the observables of $B\to D τν_τ$ is more towards the scalar current, whereas the bin-by-bin analysis of $q^2$ distribution of the differential branching fraction points to regions of $q^2$ sensitive to tensor interactions. Interestingly, the observables in $B\to D^{\ast}τν_τ$ are more sensitive to tensor interactions, and bin-by-bin analysis of this mode shows the distinct regions of $q^2$ sensitive to vector or scalar interactions. In addition to that, the $τ$ polarisation asymmetry is found to be more sensitive to NP compared to the other observables, in both decay modes.

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arXiv2015

Probing Higgs couplings at LHC and beyond

The study of the Higgs couplings following its discovery is the priority of future LHC runs. A hint of anomalous nature will be exhibited via its coupling to the Standard Model(SM) particles and open up new domain of phenomenological study of physics beyond the Standard Model. The enhanced statistics from next LHC runs will enable entry into the precision era to study the properties of Higgs with greater details. In this paper we present how one can extract Higgs couplings in future LHC runs at 14 TeV via $H \rightarrow Z Z^* \rightarrow 4 \ell$, using observables constructed from angular distributions for the Standard Model Higgs and Higgs with mixed CP configuration. We show how angular asymmetries can be used to measure the ratios of the couplings and the relative phases at LHC. We benchmark our analysis finding out the angular asymmetries and the best fit values of the ratios of the couplings for SM Higgs, CP-odd admixture, CP-even higher derivative contribution and when CP-even higher derivative contribution and CP-odd admixture are both present. In the Standard Model, $HZZ$ couplings have no momentum dependence. It is thus essential to demonstrate the momentum independence of the couplings to establish the couplings are SM like in nature. In this work we show how one can test the momentum independence of the Standard Model like coupling using angular asymmetries. We develop the necessary tools and demonstrate how to study the momentum dependence can be studied at future LHC runs.

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arXiv2013

CPT violation and triple-product correlations in B decays

The T-odd triple product (TP) asymmetries in B decays to a pair of vector mesons are treated as a good probe of CP violation because of the CPT symmetry. If CPT is no longer a good symmetry, such correlations between T-odd and CP-odd observables do not exist, and one might get unexpected nonzero TP asymmetries as a signal for CPT violation. We give a general formalism of TP asymmetries in the presence of CPT violation, either in decay or in neutral meson mixing. We also discuss how the observables depending on the transversity amplitudes are modified, and compare our expressions with the LHCb results, showing that the study of TP asymmetries might turn out to be one of the best probes for CPT violation.

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arXiv2013

Probing CPT Violation in B Systems

We discuss how a possible violation of the combined symmetry CPT in the B meson system can be investigated at the LHC. We show how a tagged and an untagged analysis of the decay modes of both B(d) and B(s) mesons can lead not only to a possible detection of a CPT-violating new physics but also to an understanding of its precise nature. The implication of CPT violation to a large mixing phase in the B(s) system is also discussed.

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arXiv2013

$B_s\to D_s K$ as a Probe of CPT Violation

We discuss some possible signals of CPT violation in the $B_s$ system that may be probed at the Large Hadron Collider (LHC). We show how one can construct combinations ofobservables coming from tagged and untagged decay rates of $B_s\to D_s^\pm K^\mp$ that can unambiguously differentiate between CPT violating and CPT conserving new physics (NP) models contributing in $B_s-\bar B_s$ mixing. We choose this particular mode as an illustrative example for two reasons: (i) In the Standard Model, there is only one decay amplitude, so it is easier to untangle any new physics; (ii) $B_s$ being a neutral meson, it is possible to unambiguously identify any sign of CPT violation that occurs only in mixing but not in decay. We define an observable which is useful to extract the CPT violating parameter in $B_s$ decay, and also discuss how far the results are applicable even if CPT violation is present in both mixing and decay.

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arXiv2011

Reconciling anomalous measurements in $B_s-\bar{B}_s$ mixing: the role of CPT-conserving and CPT-violating new physics

Recently observed anomalies in the $B_s \to J/ψϕ$ decay and the like-sign dimuon asymmetry $A^b_{sl}$ hint at possible new physics (NP) in the $\bsbsbar$ mixing. We parameterize the NP with four model-independent quantities: the magnitudes and phases of the dispersive part $M_{12}$ and the absorptive part $Γ_{12}$ of the NP contribution to the effective Hamiltonian. We constrain these parameters using the four observables $ΔM_s$, $ΔΓ_s$, the mixing phase $β_s^{J/ψϕ}$, and $A^b_{sl}$. Our quantitative fit indicates that the NP should contribute a significant dispersive as well as absorptive part. In fact, models that do not contribute a new absorptive part are disfavored at more than 99% confidence level. We extend this formalism to include CPT violation, and show that CPT violation by itself, or even in presence of CPT-conserving new physics without an absorptive part, helps only marginally in the simultaneous resolution of these anomalies. The NP absorptive contribution to $\bsbsbar$ mixing therefore seems to be essential, and would imply a large branching fraction for channels like $B_s \to τ^+ τ^-$.

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