arXiv subjects

Avirup Shaw

Publications and source records attributed to Avirup Shaw.

At least 19 recordsLinked to original sources

arXiv2026

Belle II Constraints on the Non-Minimal Universal Extra Dimensional Model

Recent measurements by the Belle II Collaboration report a branching ratio for the decay $B^+\to K^+ ν\barν$ with a 3.5$σ$ significance and deviating by 2.7$σ$ from Standard Model expectation. In this article, we interpret this experimental result through the lens of a Non-minimal Universal Extra Dimensional model, where the mass profiles and interactions among various Kaluza-Klein states differ remarkably from those in the minimal scenario. Our analysis indicates that, according to the model's parameters, the lower limit on the inverse of the compactification radius has been elevated to approximately 900 GeV. In contrast, conducting the same analysis within the model variant in which all boundary terms are nullified does not permit the determination of a lower bound on the inverse compactification radius.

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arXiv2023

Neutrino mass and leptogenesis in a hybrid seesaw model with a spontaneously broken CP

We introduce a novel hybrid framework combining type I and type II seesaw models for neutrino mass where a complex vacuum expectation value of a singlet scalar field breaks CP spontaneously. Using pragmatic organizing symmetries we demonstrate that such a model can simultaneously explain the neutrino oscillation data and generate observed baryon asymmetry through leptogenesis. Interestingly, natural choice of parameters leads to a mixed leptogenesis scenario driven by nearly degenerate scalar triplet and right handed singlet neutrino fields for which we present a detailed quantitative analysis.

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arXiv2022

Reappraisal of the minimal flavoured $Z^{\prime}$ scenario

Recent results from the intensity frontier indicate the tantalizing possibility of violation in lepton flavour universality. In light of this we revisit the minimal phenomenological $Z'$ model taking in account both vectorial and axial-vectorial flavour violating couplings to the charged leptons. We make a systematic study to identify the minimal framework that can simultaneously explain the recent results on anomalous magnetic moment of muon and electron while remaining in consonance with $R_{K^{(*)}}$, $B^0_s-\bar{B^0_s}$ mixing and angular observables in the $B^+\to K^{+*} μ^+μ^-$ channel reported by the LHCb collaboration. We demonstrate that the neutrino trident data imply a further ${\rm SU(2)}_L$ violation in the leptonic couplings of the exotic $Z'$.

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arXiv2021

The impact of nonminimal Universal Extra Dimensional model on $ΔB=2$ transitions

We measure the impact of nonvanishing boundary localised terms on $ΔB=2$ transitions in five-dimensional Universal Extra Dimensional scenario where masses and coupling strengths of several interactions of Kaluza-Klein modes are significantly modified with respect to the minimal counterpart. In such scenario we estimate the Kaluza-Klein contributions of quarks, gauge bosons and charged Higgs by evaluating the one-loop box diagrams that are responsible for the $ΔB=2$ transitions. Using the loop function (obtained from one-loop box diagrams) we determine several important elements that are involved in Wolfenstein parametrisation. Moreover, with these elements we also study the geometrical shape of unitarity triangle. Besides, we compute the quantity $ΔM_s$ scaled by the corresponding Standard Model value. Outcomes of our theoretical predictions have been compared to the allowed ranges of the corresponding observables simultaneously. Our current analysis shows that, depending on the parameters in this scenario the lower limit on the inverse of the radius of compactification can reach to an appreciable large value ($\approx 1.48$ TeV or even higher).

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arXiv2020

Collider signature of $U_1$ Leptoquark and constraints from $b\to c$ observables

One of the most popular models that is known to be able to solve the lepton flavour universality violating charged ($b\to c$) and neutral current ($b\to s$) anomalies is the Leptoquark Model. In this work we examine the {\it multijet} + $\mET$ collider signature of a vector leptoquark ($U_1$) which has the potential to mediate both the charged and neutral current processes at tree level. From our collider analysis we derive the exclusion limits on mass for the $U_1$ leptoquark at 95\% C.L. at the current and future experiment of the Large Hadron Collider. We also calculate the effect of such a leptoquark in $b\to c$ observables.

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arXiv2019

$b \to c \ell ν$ anomalies in light of extended scalar sectors

Considering the recent experimental results on exclusive semileptonic $B$ meson decays showing sizable departure from their Standard Model prediction of lepton flavor universality and keeping ongoing and proposed non-standard Higgs searches in mind, we explore the charged current flavor observables ($\mathcal{R}_{D^{(*)}}$, $\mathcal{R}_{J/ψ}$), among other $b\to c\ell ν$ transitions, in the presence of a relevant scalar current effective new physics operator. We use $B_c$ lifetime and predicted bounds on the branching fraction of $B_c \to τν$ decay as constraints. We show the allowed parameter space in terms of the real and imaginary parts of the corresponding Wilson coefficients for such interactions. Under the light of obtained results, we study the prospect of two benchmark models, rendering the Wilson coefficients real (Georgi-Machacek (GM)) and complex (Leptoquark (LQ)) respectively. We show that constraints from $b\to c\ell ν$ on GM parameters are consistent with other flavor constraints on the model, if we drop the \Babar~results. Including those disfavors the model by more than $3σ$. On the other hand, one benchmark LQ scenario, which gives rise to a single scalar current effective interaction, is still allowed within $68\%$ confidence level, albeit with a shrunk parameter space.

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arXiv2019

Looking for $B\rightarrow X_s \ell^+\ell^-$ in non-minimal Universal Extra Dimensional model

Non-vanishing boundary localised terms significantly modify the mass spectrum and various interactions among the Kaluza-Klein excited states of 5-Dimensional Universal Extra Dimensional scenario. In this scenario we compute the contributions of Kaluza-Klein excitations of gauge bosons and third generation quarks for the decay process $B\rightarrow X_s\ell^+\ell^-$ incorporating next-to-leading order QCD corrections. We estimate branching ratio as well as Forward Backward asymmetry associated with this decay process. Considering the constraints from some other $b \to s$ observables and electroweak precision data we show that significant amount of parameter space of this scenario has been able to explain the observed experimental data for this decay process. From our analysis we put lower limit on the size of the extra dimension by comparing our theoretical prediction for branching ratio with the corresponding experimental data. Depending on the values of free parameters of the present scenario, lower limit on the inverse of the radius of compactification ($R^{-1}$) can be as high as $\geq 760$ GeV. {Even this value could slightly be higher if we project the upcoming measurement by Belle II experiment.} Unfortunately, the Forward Backward asymmetry of this decay process would not provide any significant limit on $R^{-1}$ in the present model.

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arXiv2019

Collider signature of $V_2$ Leptoquark with $b\to s$ flavour observables

The Leptoquark model has been instrumental in explaining the observed lepton flavour universality violating charged ($b\to c$) and neutral ($b\to s$) current anomalies that have been the cause for substantial excitement in particle physics recently. In this article we have studied the role of one (designated as $V_2^{\frac 43}$) of the components of {\boldmath${V}_2$} Vector Leptoquark doublet with electromagnetic charge $\frac 43$ in explaining the neutral current ($b\to s$) anomalies $R_{K^{(*)}}$ and $B_s\toμ^+μ^-$. Moreover, we have performed a thorough collider search for this $V_2^{\frac 43}$ Leptoquark using $b\bar{b} \ell^+ \ell^-$ ($\ell\equiv e, μ$) final state at the Large Hadron Collider. From our collider analysis we maximally exclude the mass of the $V_2^{\frac 43}$ Leptoquark up to 2340 GeV at 95\% confidence level for the 13 TeV Large Hadron Collider for an integrated luminosity of 3000 ${\rm fb}^{-1}$. Furthermore, a significant portion of the allowed parameter space that is consistent with the neutral current ($b\to s$) observables is excluded by collider analysis.

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arXiv2019

Explaining Dark Matter and Neutrino Mass in the light of TYPE-II Seesaw Model

With the motivation of simultaneously explaining dark matter and neutrino masses, mixing angles, we have invoked the Type-II seesaw model extended by an extra $SU(2)$ doublet $Φ$. Moreover, we have imposed a $\mathbb{Z}_2$ parity on $Φ$ which remains unbroken as the vacuum expectation value of $Φ$ is zero. Consequently, the lightest neutral component of $Φ$ becomes naturally stable and can be a viable dark matter candidate. On the other hand, light Majorana masses for neutrinos have been generated following usual Type-II seesaw mechanism. Further in this framework, for the first time, we have derived the full set of vacuum stability and unitarity conditions, which must be satisfied to obtain a stable vacuum as well as to preserve the unitarity of the model respectively. Thereafter, we have performed extensive phenomenological studies of both dark matter and neutrino sectors considering all possible theoretical and current experimental constraints. Finally, we have also discussed a qualitative collider signatures of dark matter and associated odd particles at the 13 TeV Large Hadron Collider.

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arXiv2019

Reconciling dark matter, $R_{K^{(*)}}$ anomalies and $(g-2)_μ$ in an ${L_μ-L_τ}$ scenario

We propose an anomaly free unified scenario by invocation of an extra local ${\rm U(1)}_{L_μ-L_τ}$ gauge symmetry. This scenario simultaneously resolves the $R_{K^{(*)}}$ anomalies, the dark matter puzzle and the long-standing discrepancy in muon's anomalous magnetic moment. A complex scalar ($η$) having nonzero ${L_μ-L_τ}$ charge has been introduced to break this new U(1) symmetry spontaneously. Moreover, for the purpose of studying dark matter phenomenology and $R_{K^{(*)}}$ anomalies in a correlated manner, we introduce an inert ${\rm SU(2)}_L$ scalar doublet ($Φ$), a $\mathbb{Z}_2$-odd real singlet scalar ($S$) and a $\mathbb{Z}_2$-odd coloured fermion ($χ$) which transforms vectorially under the ${\rm U(1)}_{L_μ-L_τ}$ symmetry. This extra gauge symmetry provides a new gauge boson $Z_{μτ}$ which not only gives additional contribution to both $b\to s \ell\ell$ transition and $(g-2)_μ$ but also provides a crucial annihilation channel for dark matter candidate $ρ_1$ of the present scenario. This $ρ_1$ is an admixture of CP-even neutral component of $Φ$ and $S$. Our analysis shows that the low mass dark matter regime ($M_{ρ_1}\lesssim 60$ GeV) is still allowed by the experiments like XENON1T, LHC (via Higgs invisible branching) and Fermi-LAT, making the dark matter phenomenology drastically different from the standard Inert Doublet and the Scalar Singlet models. Furthermore, the present model is also fairly consistent with the observed branching ratio of $B\to X_sγ$ in $3σ$ range and is quite capable of explaining neutrino masses and mixings via Type-I seesaw mechanism if we add three right handed neutrinos in the particle spectrum. Finally, we use the latest ATLAS data of non-observation of a resonant $\ell^+\ell^-$ signal at the 13 TeV LHC to constrain the mass-coupling plane of $Z_{μτ}$.

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arXiv2018

Status of exclusion limits of the KK-parity non-conserving resonance production with updated 13 TeV LHC

Unequal strengths of boundary localised terms lead to non-conservation of the Kaluza-Klein (KK) parity in the 4 + 1 Universal Extra Dimensional model. Consequently the first excited KK-partners of Standard Model particles are not stable by any symmetry. In this article using the latest 13 TeV Large Hadron Collider (LHC) results, we revisit the resonant production of first KK-excitations of the neutral gauge bosons ($G^1$, $B^1\ \textrm{and} \ W_3^1$) and their subsequent decay. {\it Specifically $G^1$ (first KK-excitation of gluon) decays to $t\bar{t}$ pair and $B^1/W_3^1$ (first KK-excitation of electroweak gauge bosons) decay to $\ell^{+}\ell^{-} (\ell \equiv e, μ)$ pair}. We find the exclusion limits of model parameters obtained at 95\% C.L. from the non-observation of these channels have been shifted towards the lower side of the parameter space compared to our previous analysis at 8 TeV.

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arXiv2018

Revisiting the high-scale validity of Type-II seesaw model with novel LHC signature

The Type-II seesaw model is a well-motivated new physics scenario to address the origin of the neutrino mass issue. We show that this model can easily accommodate an absolutely stable vacuum until the Planck scale, however with strong limit on the exotic scalar masses and the corresponding mixing angle. We examine the model prediction at the current and future high luminosity run of the Large Hadron Collider (LHC) for the scalar masses and mixing angles fixed at such high-scale valid region. Specifically, we device the associated and pair production of the charged scalars as a new probe of the model at the LHC. We show that for a particular signal process the model can be tested with $5σ$ signal significance even at the present run of the LHC.

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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

Effects of non-minimal Universal Extra Dimension on $B\rightarrow X_sγ$

We estimate contributions from Kaluza-Klein excitations of third generation quarks and gauge bosons to the branching ratio of $B\rightarrow X_sγ$ decay process in 5-Dimensional Universal Extra Dimensional scenario with non-vanishing boundary localised terms. This model is conventionally known as non-minimal Universal Extra Dimensional model. We have derived the lower limit on the size of the extra dimension by comparing our theoretical estimation of the branching ratio which includes next-to-next-to leading order QCD corrections with its experimentally measured value. Coefficients of the boundary localised terms have also been constrained. 95 \% C.L. lower limit on inverse of radius of compactification ($R^{-1}$) can be as large as 670 GeV for some choice of the value of coefficients of boundary localised terms.

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arXiv2016

A note on gauge-fixing in the electroweak sector of nmUED

Electroweak observables are highly sensitive to the loop corrections. Therefore, a proper gauge-fixing mechanism is always needed to define the propagators which are involved in Feynman loop amplitude. With this spirit we compute gauge-fixing mechanism in five dimensional (5-D) Universal Extra-Dimensional (UED) model with boundary localised terms (BLTs). These BLTs are not 5-D operators in four-dimensional (4-D) effective theory but some sort of boundary conditions on the respective fields at the fixed points of $S^1/Z_2$ orbifold. Furthermore, these BLTs non-trivially modify the Kaluza-Klein (KK) spectra and some of the interactions among the KK-excitations compared to the minimal UED (mUED), in which, these BLTs are absent. In this note we calculate the gauge-fixing mechanism in the electroweak sector of such non-trivial UED scenario. Moreover, we discuss the composition and masses of Goldstone and any physical scalar that emerge after the symmetry breaking in this set up with different choices of gauge.

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arXiv2016

Exploring the extended scalar sector with resonances in vector boson scattering

We show that the study of scalar resonances at various vector boson scattering processes at the Large Hadron Collider can serve as a useful tool to distinguish between different extensions of the scalar sector of the Standard Model. The recent measurement of the Higgs boson properties leaves enough room for the extended scalar sectors to be relevant for such studies. The shape of the resonances, being model dependent, can shed light on the viable parameter space of a number of theoretical models.

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arXiv2016

Non-minimal UED confronts $B_{s}\rightarrowμ^{+}μ^{-}$

Addition of boundary localised kinetic and Yukawa terms to the action of a 5-dimensional Standard Model would non-trivially modify the Kaluza-Klein spectra and some of the interactions among the Kaluza-Klein excitations compared to the minimal version of this model, in which, these boundary terms are not present. In the minimal version of this framework known as Universal Extra Dimensional model, special assumptions are made about these unknown, beyond the cut-off contributions to restrict the number of unknown parameters of the theory to a minimal. We estimate the contribution of Kaluza-Klein modes to the branching ratios of $B_{s(d)}\rightarrowμ^{+}μ^{-}$ in the framework of non-minimal Universal Extra Dimensional, at one loop level. The results have been compared to the experimental data to constrain the parameters of this model. From the measured decay branching ratio of $B_s \rightarrow μ^+ μ^-$ (depending on the values of boundary localised parameters) lower limit on $R^{-1}$ can be as high as 800 GeV. We have briefly reviewed the bounds on nmUED parameter space coming from electroweak precision observables. The present analysis ($B_s \rightarrow μ^+ μ^-$) has ruled out new regions of parameter space in comparison to the analysis of electroweak data. We have revisited the bound on $R^{-1}$ in Universal Extra Dimensional model, which came out to be 454 GeV. This limit on $R^{-1}$ in Universal Extra Dimensional framework is not as competitive as the limits derived from the consideration of relic density or Standard Model Higgs boson production and decay to $W^+ W^-$. Unfortunately, $B_{d}\rightarrowμ^{+}μ^{-}$ decay branching ratio would not set any significant limit on $R^{-1}$ in a minimal or non-minimal Universal Extra Dimensional model.

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arXiv2014

KK-parity non-conservation in UED confronts LHC data

Kaluza-Klein (KK) parity can be violated in five-dimensional universal extra dimensional model with boundary-localized (kinetic or mass) terms (BLTs) at the fixed points of $S^1/Z_2$ orbifold. In this framework we study the resonant production of Kaluza-Klein excitations of the neutral electroweak gauge bosons at the LHC and their decay into an electron-positron pair or a muon-antimuon pair. We use the results (first time in our knowledge) given by the LHC experiment to constrain the mass range of the first KK-excitation of the electroweak gauge bosons ($B^1\ \textrm{and} \ W_3^1$). It is interesting to note that the LHC result puts an upper limit on the masses of the $n=1$ KK-leptons for positive values of BLT parameters and depending upon the mass of $\ell^{+}\ell^{-}$ resonance.

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