arXiv subjects

Lobsang Dhargyal

Publications and source records attributed to Lobsang Dhargyal.

13 recordsLinked to original sources

arXiv2024

Phenomenology of a universal super weak $SU(N)_{w}$ color hypothesis

In this work we will propose a new universal super weak $SU(N)_{w}$ (or self interacting vector bosons) color to which all the SM fermions are assumed to be coupled universally whose confining radius is in the range of the size of galaxies. We will argue that the model has some very interesting consequences such as it could be able to explain the observed rotation velocity anomalies in large galaxies without requirement of specific DM particle. We will also show that it could constitute most of the observed mass of a galaxy, similar like the proton mass which is mostly made up of color interaction dynamics as shown recently, which could explain the observed DM in the rotation velocities of galaxies in galaxy clusters. Also when the N is very small, we will show that it could explain the Big Bang and Hubble's law, Dark Energy, and tentatively also flavor and neutrino oscillation.

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arXiv2020

Phenomenological consequences of introducing new fermions with exotic charges to $R(K^{(*)})$, muon (g-2), the primordial Lithium problem, and dark matter

In this work we show that, by introducing two $SU(3)_{c}\times SU(2)_{L}$ singlet right handed fermions carrying opposite $U(1)_{Y}$ charges and while their left handed counterparts are singlet under $SU(3)_{c}\times SU(2)_{L}$ and neutral under $U(1)_{Y}$, in the regime where the new charged lepton masses are in the electroweak scale it will be able to explain the small neutrino masses via minimum-inverse seesaw scenario (MISS) as well as the reported $R(K^{(*)})$ and muon $(g-2)$ discrepancies. Also when the charged fermion masses are well above the electro weak scale the model can not explain the reported $R(K^{(*)})$ and muon $(g-2)$ discrepancies, but in this regime the model could explain the primordial Lithium problem. The model have another interesting extension where it can produce a stable and singlet under strong interaction scalar baryon that could constitute much of the dark matter mass of the universe which lead to a simple model where ordinary matter and dark-matter having same origin. The model can also provide new annihilation channels for the scalar singlet DM as well as allowing a doubly charged scalar whose signatures could show up in HL-LHC, ILC, CEPC etc.

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arXiv2019

A simple model to explain the observed muon sector anomalies and small neutrino masses

Since its inception, no decisive departure from the predictions of Standard Model (SM) has been reported. But recently various experiments have observed few hints of possible departure from SM predictions in lepton flavor universality observables such as $R_{K^{(*)}}$, $P_{5}^{'}$, muon (g-2), $R(D^{(*)})$ etc. Many of these observable where deviation from SM in the range of (2-4)$σ$ were observed are related to muon ($μ$) lepton. So these deviations may be some hint of a possible New Physics (NP) in the muon sector. In this work we extend the SM by introducing two SM singlet heavy charged leptons ($F_{e},\ F_μ$) whose left handed components are charged under a new $U(1)_{F}$ gauge symmetry, one color triplet lepto-quark ($ϕ_{Q}$) doublet under $SU(2)_{L}$, one inert Higgs doublet ($ϕ_{l}$), three very heavy Majorana neutrinos ($N_{iR}$), all of which are odd under a $Z_{2}$ discrete symmetry. One more scalar ($ϕ$) charged only under the $U(1)_{F}$ whose VEV give masses to the $U(1)_{F}$ gauge boson as well as the heavy leptons. With these new particles, we show that the observed anomalies in the muon sector as well as small neutrino masses can be explained with taking into account all the other experimental and theoretical constrains till date.

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arXiv2019

Exotic Leptonic solutions to observed anomalies in lepton universality observables and more

In this talk I will present the work that we did in \cite{1}\cite{2}\cite{3}\cite{4}\cite{5} related to observed lepton universality violation by Babar, Belle and LHCb in R($D^{(*)}$) and $R_{K^{(*)}}$ as well as the reported deviation in muon (g-2) by BNL. We had shown that all these anomalies as well as Baryon-genesis, Dark-matter and small neutrino masses could be explained by introducing new exotic scalars, leptons and scalar-leptoquarks only. It turn out that some of these models have very peculiar signatures such as prediction of existence of heavy stable charged particle \cite{1}\cite{2}, vector like fourth generation leptons \cite{3} or even scalar Baryonic DM candidates etc. Some of these models turn out to have very unique collider signatures such as $ee/pp \rightarrow μμ(ττ)\ +\ missing\ energy\ (ME)$, see \cite{1}\cite{2}\cite{4}. This is interesting in the sense that such peculiar signatures of these new particles can be searched in the upcoming HL-LHC or with even better chance of observing these signatures are in the upcoming precision machines such as ILC, CEPC etc.

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arXiv2018

A simple extension of SM that can explain the $(g-2)_μ$ anomaly, small neutrino mass and a dark-matter

In this work we propose a simple extension of standard-model (SM) by adding eleven new particles to it. Three heavy leptons ($f_{e},\ f_μ,\ f_τ$) singlet under the $SU(3)_{c}\times SU(2)_{L}$ carrying respective Lepton-Numbers, charged under the $U(1)_{Y}$ with $Y = -2$ and transforming under a discrete symmetry as $f_{i} \rightarrow -f_{i}$. One scalar ($ϕ_{2}$), singlet under all the SM gauge groups and transforming under the discrete symmetry as $ϕ_{2} \rightarrow -ϕ_{2}$ which does not develops a non zero vacuum-expectation-value (VEV). One more scalar ($ϕ_{3}$), singlet under all the SM gauge groups and invariant under the discrete symmetry which develops a non zero VEV ($v_{3}$) and gives masses to $f_{i}$s, $ϕ_{2}$ and neutrinos. Three right-handed neutrinos ($ν_{iR}$) and three left-handed Majorana neutrinos ($s_{iL}$). With these new additional particles added to SM we have been able to give explanations to the long standing muon (g -2) anomaly as well as the smallness of neutrino masses by the inverse see-saw mechanism. And also in this model we have a very suitable scalar dark-matter (DM) candidate in $ϕ_{2}$ with allowed mass as high as 53 GeV, although due to large Yukawa coupling required to explain the muon (g-2), its contribution to the DM relic density turn out to be too small and so it can account only a small fraction of the DM relic density of the universe.

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arXiv2018

Full angular spectrum analysis of tensor current contribution to $A_{cp}(τ\rightarrow K_{s} πν_τ)$

Babar collaboration has reported an intriguing opposite sign in the integrated decay rate asymmetry $A_{cp}(τ\rightarrow K_{s} πν_τ)$ than that of SM prediction from the known $K^{0}$ - $\bar{K^{0}}$ mixing. Babar's result deviate from the SM prediction by about 2.7$σ$. If the result stands with higher precision in the future experiments, the observed sign anomaly in the $A_{cp}(τ\rightarrow K_{s} πν_τ)$ can most likely come only from a NP. In this work we present a full angular spectrum analysis on the contribution to $A_{cp}(τ\rightarrow K_{s} πν_τ)$ coming from the tensorial term. Assuming the real part of the NP tensorial coupling is negligible compare to its imaginary part and with $A_{cp}(τ\rightarrow K_{s} πν_τ)$ and $Br(τ\rightarrow K_{s} πν_τ)$ as data points to fit the imaginary part of the NP coupling, we have been able to fit the result within 1$σ$ of the experimental values.

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arXiv2018

Search for an exotic-leptonic solution to observed anomalies in lepton universality observables in B decays and more

In this work we extend the SM by introducing only exotic scalars and leptons and show that within the reasonable error limits, both the observed anomalies in $R(D^{(*)})$ and $R_{K^{(*)}}$ can be explained along with satisfying all the constrains from nuetral meson oscillations, precision Z-pole data etc. In a trivial extension of our model with addition of three heavy right handed neutrinos, explaining the small masses of neutrinos and generation of Baryon excess via leptogenesis is possible as well. The disagreement between SM prediction and experimental data in muon (g-2) measurements can be reduced from 3.6$σ$ to around 2$σ$ in this model. Also our model has enough new particles for the scalar singlet DM to interact and generate enough annihilation to avoid over abundance problem (exotic portal), unlike the SM Higgs portal which has been ruled out.

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arXiv2018

Implications of a vector-like lepton doublet and scalar Leptoquark on $R(D^{(*)})$

We study the phenomenological constraints and consequences in the flavor sector, of introducing a new fourth generation $\mathcal{Z}_{2}$ odd vector-like lepton doublet along with a Standard Model (SM) singlet scalar and an $SU(2)_{L}$ singlet scalar leptoquark carrying electromagnetic charge of $+2/3$, both odd under a $\mathcal{Z}_{2}$. We show that with little fine tuning among the various Yukawa couplings in the new physics (NP) Lagrangian along with the CKM parameters, the model is able to push the theoretical value of $R(D^{*})^{th}$ from $0.252 \pm 0.003$ to $0.263 \pm 0.051$ and $R(D)^{th}$ from $0.300 \pm 0.008$ to $0.313 \pm 0.158$ compared to the SM value. Especially the NP contributions are able to reduce the discrepancy between experiment and theory of $R(D^{*})$ substantially compared to SM. This is quite impressive given that the model satisfy all other very stringent constrains coming from neutral meson oscillations and precision $Z$-pole data.

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arXiv2018

New tensor interaction as the source of the observed CP asymmetry in $τ\to K_{S}πν_τ$

Babar collaboration has reported an intriguing opposite sign in the integrated decay rate asymmetry $A_{cp}(τ\rightarrow K_{S}πν_τ)$ than that of SM prediction from the known K0 - $\bar{K0}$ mixing. Babar's result deviate from the SM prediction by about 2.7$σ$. If the result stands with higher precision in the future experiments, the observed sign anomaly in the $A_{cp}(τ\rightarrow K_{S}πν_τ)$ can most likely come only from some new physics occurring possibly in both hadronic as well as leptonic sectors. In this work, we will give an improved analysis of our previous work where we have illustrated that, while non-standard scalar or vector/axial-vector interactions will not contribute to the observed asymmetry in the integrated decay rate, a new tensor interaction can explain the observed anomaly. Assuming the real part of the new tensorial coupling is negligible compare to its imaginary part and with $A_{cp}(τ\rightarrow K_{S}πν_τ)$ and Br($τ\rightarrow K_{S}πν_τ$) as data points to fit the imaginary part of the NP coupling, we have been able to fit the result within 1$σ$ of the experimental values.

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arXiv2018

Explaining the observed deviation in R($D^{(*)}$) in an anomalous 2HDM

The reported combined excess of about 4$σ$, by BABAR, Belle and LHCb, in the measurements of R($D^{(*)}$) and Br(B $\rightarrow τν_τ$) from that of the standard model expectation constitute the most significant discrepancy from the standard model in collider experiments thus far(apart from the non zero neutrino masses). Here we analyze the phenomenological implications for these decay modes in a Flipped/Lepton-Specific two-Higg-doublet model with anomalously enhanced charged Higgs coupling to $τ$/b. We conclude that this extension of the standard model can give results in agreement within 1$σ$ of the experimental values for the combination of R($D^{(*)}$) and Br(B $\rightarrow τν_τ$) data.

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arXiv2018

Phenomenology of $U(1)_{F}$ extension of inert-doublet model with exotic scalars and leptons

In this work we will extend the inert-doublet model (IDM) by adding a new $U(1)_{F}$ gauge symmetry to it, under which, a $Z_{2}$ even scalar ($ϕ_{2}$) and $Z_{2}$ odd right handed component of two exotic charged leptons $(F_{eR},\ F_{μR})$, are charged. We also add one $Z_{2}$ even real scalar ($ϕ_{1}$) and one complex scalar ($ϕ$), three neutral Majorana right handed fermions ($N_{1},\ N_{2},\ N_{3}$), two left handed components of the exotic charged leptons $(F_{eL},\ F_{μL})$ as well as $F_τ$ are all odd under the $Z_{2}$, all of which are not charged under the $U(1)_{F}$. With these new particles added to the IDM, we have a model which can give two scalar DM candidates, together they can explain the present DM relic density as well as the muon (g-2) anomaly simultaneously. Also in this model the neutrino masses are generated at one loop level. One of the most peculiar feature of this model is that non-travail solution to the axial gauge anomaly free conditions lead to the prediction of a stable very heavy partner to the electron ($F_{e}$), whose present collider limit (14 TeV LHC) on its mass should be around $m_{F_{e}} \geq$ few TeV.

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arXiv2017

Search for more sensitive observables to charged scalars in $B \rightarrow D^{(*)}τν_τ$ decays

It has been known that $B \rightarrow D^{(*)} τν_τ$ are good observables in the search for the charged Higgs. The recent obervation of deviation from standard-model by almost 4$σ$ by Babar, Belle and LHCb in $R(D^{(*)})$ revived the interest in possible signal of presence of charged Higgs in these modes. But such a large deviation in the rates, where standard-model has tree level contribution, coming from a charged Higgs alone is highly unlikely. However these decay modes are good probes to search for small charged Higgs signal if we can construct sensitive observables in these modes. In this work we would like to propose four new observables which shows much more sensitivity to the presence of charged Higgs than the usual observables such as $A_λ^{D^{(*)}}$ and $A_θ^{D^{(*)}}$. These four observable are (1) $\frac{1}{A_λ^{D}}$,\ (2) $Y_{1}(q^{2}) = \frac{A^{D}_θ}{A^{D}_λ}$,\ (3) $Y_{2}(q^{2}) = \frac{dΓ(B \rightarrow D^{*}τν_τ)}{dΓ_{D}(λ_τ=+1/2) - dΓ_{D}(λ_τ=-1/2)}$ and (4) $Y_{3}(q^{2}) = (\frac{q^{2}}{m^{2}_τ})(A^{D}_λ + 1)\frac{1}{A^{D}_λ}$.

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arXiv2016

$R(D^{(*)})$ and $\mathcal{B}r(B \rightarrow τν_τ)$ in a Flipped/Lepton-Specific 2HDM with anomalously enhanced charged Higgs coupling to $τ$/b

Babar, Belle and recently LHCb has reported an excess in the measurements of $R(D^{*})$, $R(D)$ and $\mathcal{B}r(B \rightarrow τν_τ )$ than expected from SM, a possible signature of lepton flavor universality violating NP. In this work we analyze the phenomenological implications for these decay modes in a Flipped/Lepton-Specific 2HDM with anomalously enhanced Yukawa coupling of $H^{\pm}$ to $τ$/b. When experimental and theoretical errors are added in quadrature, we conclude that this phenomenological extension of SM can give results in agreement within 1$σ$ deviation for the combination of $R(D^{(*)})$ and $\mathcal{B}r(B \rightarrow τν_τ)$ compare to about 4$σ$ deviation from SM from the latest combined[Babar,Belle,LHCb] experimental data for these observables.

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