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Seesaw Mechanism in Warped Geometry

Stephan J. Huber, Qaisar Shafi

TL;DR

Problem: realize the seesaw mechanism for neutrino masses within a warped extra dimension without introducing small parameters. Approach: bulk SM singlet neutrinos with bulk Dirac masses and a Planck-brane Majorana mass, yielding an intermediate-scale seesaw through the warp factor; the seesaw scale scales as $M_ ext{Pl}\exp((2c-1)\pi kR)$. Key results: for $c<1/2$ the mechanism yields sub-eV light neutrinos with TeV-scale KK states; a concrete parameter set gives $m_\nu\sim 50\,\text{meV}$ and sterile KK states near $8.5\,\text{TeV}$, with small mixings that modestly affect precision observables. Significance: provides a natural and testable framework for neutrino masses in RS-type models with potential implications for leptogenesis and collider/precision observations.

Abstract

We show how the seesaw mechanism for neutrino masses can be realized within a five dimensional (5D) warped geometry framework. Intermediate scale standard model (SM) singlet neutrino masses, needed to explain the atmospheric and solar neutrino oscillations, are shown to be proportional to M_Pl\exp((2c-1)πkR), where c denotes the coefficient of the 5D Dirac mass term for the singlet neutrino which also has a Planck scale Majorana mass localized on the Planck-brane, and kR~11 in order to resolve the gauge hierarchy problem. The case with a bulk 5D Majorana mass term for the singlet neutrino is briefly discussed.

Seesaw Mechanism in Warped Geometry

TL;DR

Problem: realize the seesaw mechanism for neutrino masses within a warped extra dimension without introducing small parameters. Approach: bulk SM singlet neutrinos with bulk Dirac masses and a Planck-brane Majorana mass, yielding an intermediate-scale seesaw through the warp factor; the seesaw scale scales as . Key results: for the mechanism yields sub-eV light neutrinos with TeV-scale KK states; a concrete parameter set gives and sterile KK states near , with small mixings that modestly affect precision observables. Significance: provides a natural and testable framework for neutrino masses in RS-type models with potential implications for leptogenesis and collider/precision observations.

Abstract

We show how the seesaw mechanism for neutrino masses can be realized within a five dimensional (5D) warped geometry framework. Intermediate scale standard model (SM) singlet neutrino masses, needed to explain the atmospheric and solar neutrino oscillations, are shown to be proportional to M_Pl\exp((2c-1)πkR), where c denotes the coefficient of the 5D Dirac mass term for the singlet neutrino which also has a Planck scale Majorana mass localized on the Planck-brane, and kR~11 in order to resolve the gauge hierarchy problem. The case with a bulk 5D Majorana mass term for the singlet neutrino is briefly discussed.

Paper Structure

This paper contains 6 sections, 27 equations, 2 figures.

Table of Contents

  1. Introduction
  2. KK reduction with a Majorana mass term
  3. The KK spectrum
  4. The seesaw mechanism in warped geometry
  5. Discussion
  6. Conclusions

Figures (2)

  • Figure 1: The KK masses (a) and the even content (b) of the lowest KK states as a function of the Majorana mass $m_M=d\cdot \delta(y)$. We have taken $c=1/2$ and $\Omega=10^{14}$.
  • Figure 2: The wave functions of the $0_+$ and $1_+$ states in the vicinity of the TeV-brane for different values of the Majorana mass ($d=50,100,200$ and $d=100,200,400$). The left- (right-) handed components are shown in solid (dashed) lines. We have taken $c=1/2$ and $\Omega=10^{14}$.