Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Gravitational Waves from $\textit{Type-I}$ Strings in a Neutrino Mass Model

Adeela Afzal

TL;DR

The paper investigates a left-right symmetric model with a split seesaw mechanism, showing that spontaneous breaking of $SU(2)_R\times U(1)_{B-L}$ can produce type-I cosmic strings when $\beta=\lambda/(2g^2)\ll 1$, driven by a large $v_R$. Exponential wavefunction localization in extra dimensions naturally suppresses both Dirac Yukawas and the quartic coupling, yielding $M_\nu \sim -m_D M_R^{-1} m_D^T$ with $m_D \sim e^{-M_i L} v_{EW}$ and $\lambda \sim \lambda_5 e^{-4 M_\Delta L}$, hence $\beta\ll 1$. The resulting CS network has a tension $\mu_{cs}$ set by $v_R$ via $\mu_{cs} \propto v_R^2$ and emits a stochastic gravitational-wave background $\Omega_{\rm GW}(f)$ that depends on $G\mu_{cs}$ and $B(\beta)$, offering testable predictions for PTAs and future detectors. This framework links neutrino mass generation to observable cosmological signals, constraining the parameter space (notably $v_R \lesssim 10^{15}$ GeV) and motivating further work on related aspects like leptogenesis and dark matter within the same setup.

Abstract

In this work, we propose a novel realization of $\textit{type-I}$ cosmic strings arising from the spontaneous breaking of an extended gauge symmetry $SU(2)_R\times U(1)_{B-L}$ in the context of a low-scale split seesaw mechanism for neutrino mass generation. We demonstrate that the split seesaw framework, which explains the smallness of neutrino masses, naturally motivates a small scalar self-coupling $λ$. This intrinsically links the neutrino mass generation mechanism to the formation of $\textit{type-I}$ cosmic strings, where the gauge coupling dominates over the scalar self-coupling ($β\equivλ/2g^2<1$). We explore the cosmological implications of these strings, including their gravitational wave signatures that are testable in current and future experiments. Our findings establish a compelling and testable connection between neutrino mass generation and cosmic string phenomenology in an underexplored region of parameter space.

Gravitational Waves from $\textit{Type-I}$ Strings in a Neutrino Mass Model

TL;DR

The paper investigates a left-right symmetric model with a split seesaw mechanism, showing that spontaneous breaking of can produce type-I cosmic strings when , driven by a large . Exponential wavefunction localization in extra dimensions naturally suppresses both Dirac Yukawas and the quartic coupling, yielding with and , hence . The resulting CS network has a tension set by via and emits a stochastic gravitational-wave background that depends on and , offering testable predictions for PTAs and future detectors. This framework links neutrino mass generation to observable cosmological signals, constraining the parameter space (notably GeV) and motivating further work on related aspects like leptogenesis and dark matter within the same setup.

Abstract

In this work, we propose a novel realization of cosmic strings arising from the spontaneous breaking of an extended gauge symmetry in the context of a low-scale split seesaw mechanism for neutrino mass generation. We demonstrate that the split seesaw framework, which explains the smallness of neutrino masses, naturally motivates a small scalar self-coupling . This intrinsically links the neutrino mass generation mechanism to the formation of cosmic strings, where the gauge coupling dominates over the scalar self-coupling (). We explore the cosmological implications of these strings, including their gravitational wave signatures that are testable in current and future experiments. Our findings establish a compelling and testable connection between neutrino mass generation and cosmic string phenomenology in an underexplored region of parameter space.

Paper Structure

This paper contains 7 sections, 31 equations, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Cosmic Strings in a Left-Right Symmetric Model
  3. Lagrangian and Scalar Potential
  4. Mass Generation in Split Seesaw
  5. Type-I Cosmic Strings
  6. Phenomenological Implications
  7. Conclusions

Figures (4)

  • Figure 1: Neutrino mass evolution versus symmetry-breaking scale has been presented. The colored shaded region indicates the NANOGrav NANOGrav:2023gor excluded regime as shown in Fig. \ref{['fig:omegaftype1']}. The colored curves represent the different values of the exponential suppression factor. The colored stars correspond to the atmospheric scale mass, $M_\nu\simeq0.05$ eV for each exponential suppression factor. The colliders constrain the lower value $v_R\gtrsim10^5$ GeV Queiroz:2024ipo, shown as the gray shaded regime.
  • Figure 2: The evolution of GW spectra from CSs for different values of $\beta$ as shown by the vertical colored bar. We fix $v_R=10^{14}$ GeV, the amplitude of the GW spectrum decreases logarithmically with the decrease in $\beta$.
  • Figure 3: The evolution of GW spectra for type-I CSs for different values of $v_R$ corresponding to the benchmark points given in Fig. \ref{['fig:massessymmbreaking']} and indicated in the inset. The dashed gray line corresponds to $v_R\simeq1\times10^{15}$, which is not consistent with the PTAs and hence ruled out. The colored shaded regions indicate the sensitivity curves of present (solid boundaries) LIGO O3 KAGRA:2021kbb, NANOGrav NANOGrav:2023gor and future (dashed boundaries) LIGO O5, SKA Smits:2008cf, THEIA Garcia-Bellido:2021zgu, LISA Baker:2019nia, $\mu$-ARES Sesana:2019vho, BBO Corbin:2005ny, U-DECIGO Yagi:2011wgKawamura:2020pcg, CE Reitze:2019iox and ET Punturo:2010zz experiments.
  • Figure 4: The evolution of the CS tension with $\beta$ and its impact on the exponential parameter appearing in Eq. \ref{['eqn:seesawmassformula']} is shown with the vertical colored bar. The hatch region indicates the NANOGrav NANOGrav:2023gor excluded regime. The mass of the neutrino is assumed to be the atmospheric scale mass, $M_\nu\simeq0.05$ eV.