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Magnetic monopoles and high frequency gravitational waves from quasi-stable strings

Rinku Maji, Qaisar Shafi

Abstract

The spontaneous breaking of $SO(10)$ via flipped $SU(5)$ to the Standard Model yields a novel scenario in which the superheavy topologically stable GUT monopole carrying a single unit ($2π/e$) of Dirac magnetic charge emerges from the merger of a confined but topologically distinct monopole-antimonopole pair that are pulled together by a string. The $SO(10)$ breaking via the subgroup $SU(4)_c\times SU(2)_L\times SU(2)_R$, following a similar reasoning, produces a topologically stable monopole that carries two units ($4π/e$) of Dirac charge. We explore the cosmological consequences of this scenario by assuming that the monopoles and strings experience a limited number of inflationary $e$-foldings, before re-entering the horizon and ultimately forming a network of quasi-stable strings bounded by monopole-antimonopole pairs. We identify regions of the parameter space that yield an observable number density of the GUT monopole from the collapse of the appropriate string segments. The gravitational waves emitted by these quasi-stable cosmic strings lie in the Hz to kHz range, which can be tested in a number of proposed and ongoing experiments.

Magnetic monopoles and high frequency gravitational waves from quasi-stable strings

Abstract

The spontaneous breaking of via flipped to the Standard Model yields a novel scenario in which the superheavy topologically stable GUT monopole carrying a single unit () of Dirac magnetic charge emerges from the merger of a confined but topologically distinct monopole-antimonopole pair that are pulled together by a string. The breaking via the subgroup , following a similar reasoning, produces a topologically stable monopole that carries two units () of Dirac charge. We explore the cosmological consequences of this scenario by assuming that the monopoles and strings experience a limited number of inflationary -foldings, before re-entering the horizon and ultimately forming a network of quasi-stable strings bounded by monopole-antimonopole pairs. We identify regions of the parameter space that yield an observable number density of the GUT monopole from the collapse of the appropriate string segments. The gravitational waves emitted by these quasi-stable cosmic strings lie in the Hz to kHz range, which can be tested in a number of proposed and ongoing experiments.
Paper Structure (5 sections, 10 equations, 5 figures)

This paper contains 5 sections, 10 equations, 5 figures.

Table of Contents

  1. Introduction
  2. Monopoles connected by strings in SO(10) symmetry breakings
  3. Quasi-stable string and high frequency gravitational waves
  4. Conclusions
  5. Acknowledgment

Figures (5)

  • Figure 1: Merger of $U(1)_X$ and $U(1)_Z$ monopoles before the electroweak symmetry breaking.
  • Figure 2: Emergence of $SO(10)$ GUT monopole with magnetic charge $2\pi/e$ from the merger of a $U(1)_X$ monopole and a $U(1)_Z$ antimonopole following the electroweak symmetry breaking.
  • Figure 3: Emergence of monopole of charge $4\pi/e$ from the merger of confined $U(1)_{R}$ and $U(1)_{B-L}$ monopoles following the electroweak symmetry breaking.
  • Figure 4: Gravitational wave background from the quasi-stable string network for $G\mu = 10^{-8}-10^{-5}$ with a varying monopole horizon re-entry time $t_M=10^{-25}-10^{-19}$ sec, which can give rise to a comoving monopole number density $Y_M\sim 10^{-27}-10^{-37}$. We have depicted the power-law integrated sensitivity curves Thrane:2013oyaSchmitz:2020syl for planned experiments near Hz to kHz frequency region, namely, HLVK KAGRA:2013rdx, ET Mentasti:2020yyd, CE Regimbau:2016ike, DECIGO Sato_2017, and BBO Crowder:2005nrCorbin:2005ny. The gray shaded region shows the bound for a scale-invariant gravitational wave spectrum for $f_{\rm high}/f_{\rm low}=10^7$ arising from the bound on $\Delta N_{\rm eff}$ in the BBN and CMB data.
  • Figure 5: Gravitational wave background from the quasi-stable string network for $G\mu = 10^{-8}$, $10^{-7}$, and $10^{-6}$ with a varying monopole horizon re-entry time $t_M=10^{-16}$, $10^{-10}$, $10^{-4}$ and $10^2$ sec. We also display the power-law integrated sensitivity curves Thrane:2013oyaSchmitz:2020syl for planned experiments near Hz to kHz frequency region, namely, HLVK KAGRA:2013rdx, ET Mentasti:2020yyd, CE Regimbau:2016ike, DECIGO Sato_2017, BBO Crowder:2005nrCorbin:2005ny, LISA and SKA. The gray shaded region shows the bound for a scale-invariant gravitational wave spectrum for $f_{\rm high}/f_{\rm low}=10^7$ arising from the bound on $\Delta N_{\rm eff}$ in the BBN and CMB data.