We study the impact of the mixing (LR mixing) between the standard model $W$ boson and its hypothetical, heavier right-handed parter ${W}_{R}$ on the neutrinoless double beta decay ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay) rate. Our study is done in the minimal left-right symmetric model assuming a type-II dominance scenario with charge conjugation as the left-right symmetry. We then show that the $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay rate may be dominated by the contribution proportional to this LR mixing, which at the hadronic level induces the leading-order contribution to the interaction between two pions and two charged leptons. The resulting long-range pion exchange contribution can significantly enhance the decay rate compared to previously considered short-range contributions. Finally, we find that even if future cosmological experiments rule out the inverted hierarchy for neutrino masses, there are still good prospects for a positive signal in the next generation of $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay experiments.

/pdf/left-right-symmetry-and-leading-contributions-to-2oqkjo0433.pdf

Left-Right Symmetry and Leading Contributions to Neutrinoless Double Beta Decay.

/pdf/the-mu2e-experiment-at-fermilab-132nwkc399.pdf

The Mu2e Experiment at Fermilab

A low energy non-unitary leptonic m ixing m atrix isa genericfeatureofm any extensionsofthe Standard M odel. In such a case,the task offuture precision neutrino oscillation experim ents is m ore am bitiousthan m easuring the three m ixing anglesand the leptonic (Dirac)CP-phase, i.e., theaccessibleparam etersofaunitary leptonicm ixingm atrix.A non-unitary m ixingm atrix has13

http://inspirehep.net/record/816102/files/arXiv:0903.3986.pdf

Probing non-unitary m ixing and C P-violation at a N eutrino Factory

Using a low-energy effective field theory approach, we study some properties of models with large extra dimensions, in which quarks and leptons have localized wave functions in the extra dimensions. We consider models with two types of gauge groups: (i) the Standard-Model gauge group, and (ii) the left-right symmetric gauge group. Our main focus is on the lepton sector of models with $n=2$ extra dimensions, in particular, neutrino masses and mixing. We analyze the requisite conditions that the models must satisfy to be in accord with data and present a solution for lepton wave functions in the extra dimensions that fulfils these conditions. As part of our work, we also present a new solution for quark wave function centers. Issues with flavor-changing neutral-current effects are assessed. Finally, we remark on baryogenesis and dark matter in these models.

Neutrino masses and mixing in models with large extra dimensions and localized fermions

The latest measurements of the anomalous muon magnetic moment $a^{}_\mu \equiv (g^{}_\mu - 2)/2$ show a $4.2\sigma$ discrepancy between the theoretical prediction of the Standard Model and the experimental observations. In order to account for such a discrepancy, we consider a possible extension of the type-(I+II) seesaw model for neutrino mass generation with a gauged $L^{}_\mu - L^{}_\tau$ symmetry. By explicitly constructing an economical model with only one extra scalar singlet, we demonstrate that the gauge symmetry $U(1)^{}_{L^{}_\mu - L^{}_\tau}$ and its spontaneous breaking are crucially important not only for explaining the muon $(g - 2)$ result but also for generating neutrino masses and leptonic flavor mixing. Various phenomenological implications and experimental constraints on the model parameters are also discussed. 

Neutrino masses, leptonic flavor mixing, and muon (g−2) in the seesaw model with the gauge symmetry *

A comparative study of 0νββ decay in symmetric and asymmetric left-right model

We consider a gauged $U(1)_{L_\mu-L_\tau}$ extension of the left-right symmetric theory in order to simultaneously explain neutrino mass, mixing and the muon anomalous magnetic moment. We get sizeable contribution from the interaction of the new light gauge boson $Z_{\mu\tau}$ of the $U(1)_{L_\mu-L_\tau}$ symmetry with muons which can individually satisfy the current bounds on muon $(g-2)$ anomaly ($\Delta a_\mu$). The other positive contributions to $\Delta a_\mu$ come from the interactions of singly charged gauge bosons $W_L$, $W_R$ with heavy neutral fermions and that of neutral CP-even scalars with muons. The interaction of $W_L$ with heavy neutrino is facilitated by inverse seesaw mechanism which allows large light-heavy neutrino mixing and explains neutrino mass in our model. CP-even scalars with mass around few hundreds GeV can also satisfy the entire current muon anomaly bound. The results show that the model gives a small but non-negligible contribution to $\Delta a_\mu$ thereby eliminating the entire deviation in theoretical prediction and experimental result of muon $(g-2)$ anomaly. We have briefly presented a comparative study for symmetric and asymmetric left-right symmetric model in context of various contribution to $\Delta a_\mu$. We also discuss how the generation of neutrino mass is affected when left-right symmetry breaks down to Standard Model symmetry via various choices of scalars.

/pdf/neutrino-mass-mixing-and-muon-g-2-explanation-in-u-1-l-mu-l-23v53s08o7.pdf

Neutrino mass, mixing and muon $g-2$ explanation in $U(1)_{L_\mu-L_\tau}$ extension of left-right theory.

We explore an $A_4$-symmetric flavor based left-right symmetric model with linear seesaw mechanism and study the associated neutrino phenomenology. The framework offers the advantage of studying neutrino mass, non-unitarity effects in lepton sector, lepton flavour violation and CP violation. The fermion content of the model includes usual quarks, leptons along with additional sterile fermion per generation while the scalar content includes Higgs doublets and scalar bidoublet. We study analytically as well as numerically the correlation between different model parameters and their dependence on experimentally determined neutrino observables.

$A_4$ realization of left-right symmetric linear seesaw

We derive the lower bound on the absolute scale of lightest neutrino mass for normal hierarchy and inverted hierarchy pattern of light neutrinos by studying the new physics contributions to charged lepton flavour violations in the framework of a TeV scale left-right symmetric model. In the model, the fermion sector comprises the usual quarks and leptons plus a fermion singlet per generation and the scalar sector consists of isospin doublets, triplets and a bidoublet. The framework allows large light-heavy neutrino mixing where the light neutrino mass formula is governed by a natural type-II seesaw mechanism, unlike the generic type-II seesaw dominance which assumes suppressed light-heavy neutrino mixing. We demonstrate how sizeable loop-induced contribution to light neutrino mass is kept under control such that the light neutrino mass formula is dominantly explained by the type-II seesaw mechanism. We examine the heavy neutrino contributions with large light-heavy neutrino mixing to charged lepton flavour violating processes like $\mu \to e \gamma$, $\mu \to 3 e$ and $\mu \to e$ conversion inside a nucleus. We present a complementary study between neutrinoless double beta decay and charged lepton flavour violation taking into account single beta decay bound, double beta decay bound and cosmology bounds on the sum of light neutrino masses.

Effect of large light-heavy neutrino mixing and natural type-II seesaw dominance to lepton flavor violation and neutrinoless double beta decay

We consider a gauged $$ \mathrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$
 extension of the left-right symmetric theory in order to simultaneously explain neutrino mass, mixing and the muon anomalous magnetic moment. We get sizeable contribution from the interaction of the new light gauge boson Zμτ of the $$ \mathrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$
 symmetry with muons which can individually satisfy the current bounds on muon (g − 2) anomaly (∆aμ). The other positive contributions to ∆aμ come from the interactions of singly charged gauge bosons WL, WR with heavy neutral fermions and that of neutral CP-even scalars with muons. The interaction of WL with heavy neutrino is facilitated by inverse seesaw mechanism which allows large light-heavy neutrino mixing and explains neutrino mass in our model. CP-even scalars with mass around few hundreds GeV can also satisfy the entire current muon anomaly bound. The results show that the model gives a small but non-negligible contribution to ∆aμ thereby eliminating the entire deviation in theoretical prediction and experimental result of muon (g − 2) anomaly. We have briefly presented a comparative study for symmetric and asymmetric left-right symmetric model in context of various contribution to ∆aμ. We also discuss how the generation of neutrino mass is affected when left-right symmetry breaks down to Standard Model symmetry via various choices of scalars.

/pdf/neutrino-mass-mixing-and-muon-g-2-explanation-in-u-1-l-m-l-t-2sbx9bc5z3.pdf

Prativa Pritimita

Papers

A comparative study of 0νββ decay in symmetric and asymmetric left-right model

Neutrino mass, mixing and muon $g-2$ explanation in $U(1)_{L_\mu-L_\tau}$ extension of left-right theory.

$A_4$ realization of left-right symmetric linear seesaw

Effect of large light-heavy neutrino mixing and natural type-II seesaw dominance to lepton flavor violation and neutrinoless double beta decay

Neutrino mass, mixing and muon g − 2 explanation in U 1 L μ − L τ $$ \mathrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$ extension of left-right theory