# Naturally light Dirac neutrino in Left-Right Symmetric Model

## Abstract

We study the possibility of generating tiny Dirac masses of neutrinos in Left-Right Symmetric Model (LRSM) without requiring the existence of any additional symmetries. The charged fermions acquire masses through a universal seesaw mechanism due to the presence of additional vector like fermions. The neutrinos acquire a one-loop Dirac mass from the same additional vector like charged leptons without requiring any additional discrete symmetries. The model can also be extended by an additional Z {sub 2} symmetry in order to have a scotogenic version of this scenario predicting a stable dark matter candidate. We show that the latest Planck upper bound on the effective number of relativistic degrees of freedom N {sub eff}=3.15 ± 0.23 tightly constrains the right sector gauge boson masses to be heavier than 3.548 TeV . This bound on gauge boson mass also affects the allowed values of right scalar doublet dark matter mass from the requirement of satisfying the Planck bound on dark matter relic abundance. We also discuss the possible implications of such a scenario in charged lepton flavour violation and generating observable electric dipole moment of leptons.

- Authors:

- Department of Physics, Indian Institute of Technology Guwahati, Assam-781039 (India)
- Institute of Physics, HBNI, Sachivalaya Marg, Bhubaneshwar-751005 (India)

- Publication Date:

- OSTI Identifier:
- 22676180

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2017; Journal Issue: 06; Other Information: Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ABUNDANCE; BOSONS; DEGREES OF FREEDOM; ELECTRIC DIPOLE MOMENTS; ELECTRIC DIPOLES; FLAVOR MODEL; MASS; NEUTRINOS; NONLUMINOUS MATTER; RELATIVISTIC RANGE; SYMMETRY; TEV RANGE; VISIBLE RADIATION

### Citation Formats

```
Borah, Debasish, and Dasgupta, Arnab, E-mail: dborah@iitg.ernet.in, E-mail: arnab.d@iopb.res.in.
```*Naturally light Dirac neutrino in Left-Right Symmetric Model*. United States: N. p., 2017.
Web. doi:10.1088/1475-7516/2017/06/003.

```
Borah, Debasish, & Dasgupta, Arnab, E-mail: dborah@iitg.ernet.in, E-mail: arnab.d@iopb.res.in.
```*Naturally light Dirac neutrino in Left-Right Symmetric Model*. United States. doi:10.1088/1475-7516/2017/06/003.

```
Borah, Debasish, and Dasgupta, Arnab, E-mail: dborah@iitg.ernet.in, E-mail: arnab.d@iopb.res.in. Thu .
"Naturally light Dirac neutrino in Left-Right Symmetric Model". United States.
doi:10.1088/1475-7516/2017/06/003.
```

```
@article{osti_22676180,
```

title = {Naturally light Dirac neutrino in Left-Right Symmetric Model},

author = {Borah, Debasish and Dasgupta, Arnab, E-mail: dborah@iitg.ernet.in, E-mail: arnab.d@iopb.res.in},

abstractNote = {We study the possibility of generating tiny Dirac masses of neutrinos in Left-Right Symmetric Model (LRSM) without requiring the existence of any additional symmetries. The charged fermions acquire masses through a universal seesaw mechanism due to the presence of additional vector like fermions. The neutrinos acquire a one-loop Dirac mass from the same additional vector like charged leptons without requiring any additional discrete symmetries. The model can also be extended by an additional Z {sub 2} symmetry in order to have a scotogenic version of this scenario predicting a stable dark matter candidate. We show that the latest Planck upper bound on the effective number of relativistic degrees of freedom N {sub eff}=3.15 ± 0.23 tightly constrains the right sector gauge boson masses to be heavier than 3.548 TeV . This bound on gauge boson mass also affects the allowed values of right scalar doublet dark matter mass from the requirement of satisfying the Planck bound on dark matter relic abundance. We also discuss the possible implications of such a scenario in charged lepton flavour violation and generating observable electric dipole moment of leptons.},

doi = {10.1088/1475-7516/2017/06/003},

journal = {Journal of Cosmology and Astroparticle Physics},

number = 06,

volume = 2017,

place = {United States},

year = {Thu Jun 01 00:00:00 EDT 2017},

month = {Thu Jun 01 00:00:00 EDT 2017}

}