arXiv subjects

Rukmani Mohanta

Publications and source records attributed to Rukmani Mohanta.

At least 91 records · Page 5Linked to original sources

arXiv2017

Neutrino Mass and Neutrinoless double beta decay in SO(10) GUT with Pati-Salam symmetry

We demonstrate how a class of non-supersymmetric $SO(10)$ GUT with asymmetric left-right theory $SU(2)_L \times U(1)_R \times U(1)_{B-L} \times SU(3)_C$ and Pati-Salam theory $SU(2)_L \times SU(2)_R \times SU(4)_C$ as intermediate symmetry breaking steps leads to successful gauge coupling unification satisfying proton decay constraints. The motivation behind this work is two fold: firstly to study the renormalization group evolution equations for gauge couplings by keeping right-handed neutral gauge boson $Z_R$ around LHC energy range leading interesting dilepton searches at collider while fixing charge partner of the gauge boson $W_R$ at very high scale; secondly to explain neutrino masses and associated lepton number violating process like neutrinoless double beta decay in three possible cases depending on how $SU(2)_L \times U(1)_R \times U(1)_{B-L} \times SU(3)_C$ breaks down to SM. We include one extra fermion singlet per generation in order to implement gauged extended seesaw where light neutrino mass is governed by natural type-II seesaw mechanism whereas type-I seesaw contribution is exactly canceled out. Since light neutrino mass formula is independent of Dirac neutrino mass matrix, the value of Dirac neutrino mass is taken to be up-type quark mass matrix which is a characteristics of Pati-Salam symmetry relating quarks with leptons. We present analytic relation for effective Majorana mass parameter and corresponding half-life arising from new physics contributions due to purely left-handed currents through exchange of heavy right-handed neutrinos and sterile neutrinos. We numerically estimate effective Majorana mass parameter and half-life vs. lightest neutrino mass and derive lower bound on lightest neutrino mass by saturating with experimental bounds like GERDA Phase-II, KamLANDZen and EXO.

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arXiv2017

New Physics effects in charm meson decays involving $c \to u l^+ l^- (l_i^\mp l_j^\pm)$ transitions

We study the effect of scalar leptoquark and $Z^\prime$ boson on the rare decays of $D$ mesons involving flavour changing transitions $c \to u l^+ l^- (l^\mp_i l^\pm_j)$. We constrain the new physics parameter space using the branching ratio of the rare decay mode $D^0 \to μ^+ μ^-$ and the $D^0-\bar D^0$ oscillation data. We compute the branching ratios, forward-backward asymmetry parameters and flat terms in $D^{+(0)} \to π^{+(0)} μ^+ μ^-$ processes using the constrained parameters. The branching ratios of the lepton flavour violating $D$ meson decays, such as $D^0 \to μe, ~τe$ and $D^{+(0)} \to π^{+(0)} μ^- e^+$ are also investigated.

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arXiv2017

Explaining the $R_{K}$ and $R_{D^{(*)}}$ anomalies with vector leptoquarks

Recently the $B$ factories BaBar and Belle as well as the LHCb experiment have reported several anomalies in the semileptonic $B$ meson decays such as $R_{K}$ and $R_{D^{(*)}}$ etc. We investigate these deviations by considering the vector leptoquarks relevant for both $b \to s l^+ l^-$ and $b \to c l \bar ν_l$ transitions. The leptoquark parameter space is constrained by using the experimentally measured branching ratios of $B_s \to l^+ l^-$, $\bar B \to X_s l^+ l^- (ν\bar ν)$ and $B_u^+ \to l^+ ν_l$ processes. Using the constrained leptoquark couplings, we compute the branching ratios, forward-backward asymmetries, $τ$ and $D^*$ polarization parameters in the $\bar B \to D^{(*)} l \bar ν_l$ processes. We find that the vector leptoquarks can explain both $R_{D^{(*)}}$ and $R_K$ anomalies simultaneously. Furthermore, we study the rare leptonic $B_{u, c}^* \to l \barν$ decay processes in this model.

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arXiv2017

Rare semileptonic $B \to K(π)l_i^- l_j^+$ decay in vector leptoquark model

We investigate the consequence of vector leptoquarks on the rare semileptonic lepton flavour violating decays of $B$ meson which are more promising and effective channels to probe the new physics signal. We constrain the resulting new leptoquark parameter space by using the branching ratios of $B_{s, d} \to l^+ l^-$, $K_L \to l^+ l^-$ and $τ^- \to l^- γ$ processes. We estimate the branching ratios of rare lepton flavour violating $B \to K(π)l_i^- l_j^+$ processes using the constrained leptoquark couplings. We also compute the forward-backward asymmetries and the lepton non-universality parameters of the LFV decays in the vector leptoquark model. Furthermore, we study the effect of vector leptoquark on $(g-2)_μ$ anomaly.

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arXiv2017

Impact of leptoquarks in semileptonic B decays

We study the impact of vector leptoquarks on the recent anomalies in semileptonic $B$ meson decays such as $R_K$ and $R_{D^{(*)}}$ etc. We constrain the leptoquark couplings by using the existing data on the branching ratios of $B_s \to l^+ l^-$ and $\bar{B} \to X_s l^+ l^-$ processes, where $l=e,μ,τ$. We estimate the branching ratios of $\bar B \to D^{(*)} l \bar ν_l$ processes using the constrained leptoquark parameter space. We also investigate the possibility of simultaneous explanation of $R_{D^{(*)}}$, $R_K$ anomalies in this model.

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arXiv2016

Study of the rare decays $B_{s,d}^* \to μ^+ μ^-$

We investigate the effect of scalar leptoquarks and family non-universal $Z^\prime$ boson on the rare leptonic decays of $B_{s, d}^*$ mesons, mediated by the FCNC transitions $b \to (d, s) l^+ l^-$. They are sensitive to a variety of new physics operators as opposed to the $B_{s,d}$ leptonic modes and hence, can provide an ideal testing ground to look for new physics beyond the standard model. We work out the constraint on new physics parameter space using the measured branching ratios of $B_{d, s} \to μ^+ μ^-$ processes and the $B_q - \bar B_q$ mixing data. Using the constrained parameters we estimate the branching ratios of $B_{d,s} \to μ^+ μ^-~(e^+ e^-)$ processes. We find that the branching ratios are reasonably enhanced from their corresponding standard model values in the $X(3,2,1/6)$ leptoquark model and are expected to be within the reach of Run II/III of LHC experiments.

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arXiv2016

Effects of scalar leptoquark on semileptonic $Λ_b$ decays

We study the scalar leptoquark effects on the rare semileptonic decays of $Λ_b$ baryon, governed by the quark level transition $b \to s l^+ l^-$. We estimate the branching ratios, forward-backward asymmetries, lepton polarization parameters and the lepton flavour non-universality effects in these decay channels. We find significant deviations from the corresponding standard model predictions in some of the observables due to leptoquark effects. We also investigate the lepton flavour violating decays $Λ_b \to Λl_i^- l_j^+$, the branching ratios of which are found to be ${\cal O}(10^{-10} - 10^{-9})$.

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arXiv2016

Lepton flavour violating B meson decays via scalar leptoquark

We study the effect of scalar leptoquarks in the lepton flavour violating $B$ meson decays induced by the flavour changing transitions $b \to q l_i^+ l_j^-$ with $q=s,d$. In the standard model these transitions are extremely rare as they are either two-loop suppressed or proceed via box diagrams with tiny neutrino masses in the loop. However, in the leptoquark model they can occur at tree level and are expected to have significantly large branching ratios. The leptoquark parameter space is constrained using the experimental limits on the branching ratios of $B_q \rightarrow l^+ l^-$ processes. Using such constrained parameter space, we predict the branching ratios of LFV semileptonic $B$ meson decays, such as $B^+ \to K^+ (π^+) l_i^+ l_j^-$, $B^+ \to (K^{* +}, ρ^+) l_i^+ l_j^-$ and $B_s \to ϕl_i^+ l_j^-$, which are found to be within the experimental reach of LHCb and the upcoming Belle II experiments. We also investigate the rare leptonic $K_{L, S} \to μ^+ μ^- (e^+ e^-)$ and $K_{L} \to μ^\mp e^\pm$ decays in the leptoquark model.

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arXiv2016

Study of the rare semileptonic decays $B_d^0 \to K^* l^+ l^-$ in scalar leptoquark model

We study the effect of scalar leptoquarks on the exclusive rare $B$ meson decays $\bar{B}_d^0 \rightarrow \bar{K}^{* 0}\left(\rightarrow K^-π^+\right) l^+ l^-$ in the full kinematically accessible physical region. We work out the constraints on leptoquark parameter space using the measured branching ratio of $B_s \rightarrow μ^+ μ^-$ process by the CMS and LHCb collaborations. We compute the branching ratio, forward-backward asymmetry and isospin asymmetry distribution using the constrained parameter space. We also look into various form factor independent and CP violating observables in the scalar leptoquark model.

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arXiv2016

Leptoquark effects on $b \to s ν\barν$ and $B \to K l^+ l^-$ decay processes

We study the rare semileptonic decays of $B$ mesons induced by $b \to s ν\barν$ as well as $b \to s l^+ l^-$ transitions in the scalar leptoquark model where the leptoquarks transform as $(3,2,7/6)$ and $(3,2,1/6)$ under the standard model gauge group. The leptoquark parameter space is constrained using the most recent experimental results on ${\rm Br}(B_s \rightarrow μ^+ μ^-)$ and ${\rm Br}(B_d \to X_s μ^+ μ^-)$ processes. Considering only the baryon number conserving leptoquark interactions, we estimate the branching ratios for the exclusive $\bar{B} \rightarrow \bar{K}^{(*)} ν\barν$ and inclusive $B \rightarrow X_s ν\barν$ decay processes by using the constraint parameters. We also obtain the low recoil (large lepton invariant mass, i.e., $q^2 \sim m^2_b$) predictions for the angular distribution of $\bar B \rightarrow \bar{K} l^+ l^-$ process and several other observables including the flat term and lepton flavour non-universality factor in this model.

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arXiv2015

Scalar leptoquarks and the rare B meson decays

We study some rare decays of $B$ meson involving the quark level transition $b \to q l^+l^- (q=d,s)$ in the scalar leptoquark model. We constrain the leptoquark parameter space using the recently measured branching ratios of $B_{s,d} \to μ^+ μ^-$ processes. Using such parameters, we obtain the branching ratios, direct CP violation parameters and isospin asymmetries in $B \to K μ^+ μ^-$ and $B \to πμ^+ μ^-$ processes. We also obtain the branching ratios for some lepton flavour violating decays $B \to l_i^+ l_j^-$. We find that the various anomalies associated with the isospin asymmetries of $B \to K μ^+ μ^-$ process can be explained in the scalar leptoquark model.

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arXiv2010

Probing CP violation in the neutrino sector with magic baseline experiments

We investigate the effect of CP violation in the leptonic sector. Due to the tiny neutrino masses its value is predicted to be very small and it is far beyond the experimental reach of the current experiments. Recently, the magic baseline experiment from CERN to INO (Indian Neutrino Observatory) with L=7152 km has been proposed to get a sensitive limit on $\sin θ_{13}$. We show that due to such magic baseline neutrino beam it is possible to observe CP violation in the neutrino sector upto several percent for the beam energy between (1-10) GeV.

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arXiv2010

SM with four generations: Selected implications for rare B and K decays

We extend our recent work and study implications of the Standard Model with four generations (SM4) for rare B and K decays. We again take seriously the several 2-3 $σ$ anomalies seen in B, $B_s$ decays and interpret them in the context of this simple extension of the SM. SM4 is also of course of considerable interest for its potential relevance to dynamical electroweak symmetry breaking and to baryogenesis. Using experimental information from processes such as $B \to X_s γ$, $B_d$ and $B_s$ mixings, indirect CP-violation from $K_L \to ππ$ etc along with oblique corrections, we constrain the relevant parameter space of the SM4, and find $m_{t'}$ of about 400-600 GeV with a mixing angle $| V_{t'b}^*V_{t's}|$ in the range of about (0.05 to 1.4)$\times 10^{-2}$ and with an appreciable CP-odd associated phase, are favored by the current data. Given the unique role of the CP asymmetry in $B_s \to ψϕ$ due to its gold-plated nature, correlation of that with many other interesting observables, including the semileptonic asymmetry ($A_{SL}$) are studied in SM4. We also identify several processes, such as $B \to X_s ν\barν$, $K_L \to π^0 ν\bar ν$ etc, that are significantly different in SM4 from the SM. Experimentally the very distinctive process $B_s\to μ^+μ^-$ is also discussed; the branching ratio can be larger or smaller than in SM, $(3.2 \to 4.2)\times 10^{-9}$, by a factor of ${\cal{O}}(3)$.

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arXiv2009

The fourth family: a simple explanation for the observed pattern of anomalies in B-CP asymmetries

We show that a fourth family of quarks with $m_{t'}$ in the range of (400 - 600) GeV provides a rather simple explanation for the several indications of new physics that have been observed involving CP asymmetries of the b-quark. The built-in hierarchy of the 4$\times$4 mixing matrix is such that the $t'$ readily provides a needed {\it perturbation} ($\approx 15%$) to $\sin 2 β$ as measured in $B \to ψK_s$ and simultaneously is the dominant source of CP asymmetry in $B_s \to ψϕ$. The correlation between CP asymmetries in $B_s \toψϕ$ and $B_d\toϕK_s$ suggests $m_{t'} \approx$ (400 - 600) GeV. Such heavy masses point to the tantalizing possibility that the 4th family plays an important role in the electroweak symmetry breaking.

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arXiv2003

New physics effects on the CP asymmetries in B -> phi K_S and B -> eta' K_S decays

Within the standard model (SM), the time dependent CP asymmetries in B -> psi K_S, B -> eta' K_S and B -> phi K_S are expected to give the same result i.e. sin (2 beta). However recent measurements of the mixing induced CP asymmetries in B -> phi K_S and B -> eta' K_S modes give results whose central values differ from SM expectations. We explore the effects of new physics in the two Higgs doublet model (THDM), which allows tree level flavor changing neutral currents (so called Model III), and the model with extra vector like down quark (VLDQ). We find that the observed mixing induced CP asymmetry for B -> phi K_S can not be accommodated by the THDM, but can be explained in the VLDQ model and both models can explain the observed asymmetry for B -> eta' K_S mode.

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arXiv2002

Transverse $τ$ polarization in $B_c \to τ\bar ν_τ γ$ decay

The possible transverse polarization of the $τ$-lepton, which is $T$-odd and can be used to measure CP-violation, is estimated precisely in the radiative decay mode $B_c \to τ\bar ν_τγ$ with possible parameters for the multi Higgs doublet model and the R-parity violating supersymmetric model. We find that the up-bound of the transverse polarization with possible parameters in the models is at very different levels i.e. it can be $\leq 15\sim 23%$ for the former but $\leq 0.1 %$ for the latter, and it is accessible experimentally soon.

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arXiv1999

Weak Radiative Decay Lambda_b to Lambda gamma and Quark-Confined Effects in the Covariant Oscillator Quark Model

Motivated by the observation of the decay B to K* gamma by the CLEO collaboration, we have systematically analyzed the weak radiative decay Lambda_b to Lambda gamma, evaluating the confined effects of quarks in the covariant oscillator quark model. This decay process receives both short distance (electromagnetic penguins at the one loop level) the long distance contributions in the quark level. The long distance contributions are analyzed using the vector meson dominance (VMD) method. The estimated branching ratio is found to be 0.23 times 10^-5.

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arXiv1999

Exclusive Weak Radiative Decays of B Mesons in the Covariant Oscillator Quark Model

Exclusive weak radiative B meson decays are studied using the covariant oscillator quark model. The branching ratios for the processes B0 to K*0 gamma and B to K* gamma have been estimated. These are in reasonable agreement with the available experimental data. The calculation has been extended to the CKM-suppressed decay processes B- to rho- gamma and Bs to K*0 gamma .

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