NANOGrav and PPTA Tension: Gravity Waves, Cosmic Strings, and Inflation. (arXiv:2104.02016v1 [hep-ph])
<a href="http://arxiv.org/find/hep-ph/1/au:+Lazarides_G/0/1/0/all/0/1">George Lazarides</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Maji_R/0/1/0/all/0/1">Rinku Maji</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Shafi_Q/0/1/0/all/0/1">Qaisar Shafi</a>
The NANOGrav collaboration has recently presented its pulsar timing array
data which seem compatible with the presence of a stochastic gravity wave
background emitted by cosmic strings with a dimensionless string tension
$Gmusimeq 2times 10^{-11}-3times 10^{-10}$ at $95%$ confidence level ($G$
is Newton’s constant and $mu$ denotes the string tension). However, there is
some tension between these results and the previous pulsar timing array bound
$Gmulesssim 4times 10^{-11}$ from the PPTA experiment. We propose a
relaxation of this tension by invoking primordial inflation which partially
inflates the string network. The latter re-enters the horizon at later times
after the end of inflation, and thus the short string loops are not produced.
This leads to a reduction of the gravity wave spectrum which is more pronounced
at higher frequencies. The reconciliation of the NANOGrav results with the PPTA
bound is possible provided that the strings re-enter the horizon at adequately
late times. We consider an example of a realistic $SO(10)$ model incorporating
successful inflation driven by a gauge singlet real scalar field with a
Coleman-Weinberg potential. This model leads to the production of intermediate
scale topologically stable cosmic strings that survive inflation. We show
regions of the parameter space where the tension between NANOGrav and PPTA is
alleviated. Finally, we present an example in which both monopoles and strings
survive inflation with the above tension resolved.
The NANOGrav collaboration has recently presented its pulsar timing array
data which seem compatible with the presence of a stochastic gravity wave
background emitted by cosmic strings with a dimensionless string tension
$Gmusimeq 2times 10^{-11}-3times 10^{-10}$ at $95%$ confidence level ($G$
is Newton’s constant and $mu$ denotes the string tension). However, there is
some tension between these results and the previous pulsar timing array bound
$Gmulesssim 4times 10^{-11}$ from the PPTA experiment. We propose a
relaxation of this tension by invoking primordial inflation which partially
inflates the string network. The latter re-enters the horizon at later times
after the end of inflation, and thus the short string loops are not produced.
This leads to a reduction of the gravity wave spectrum which is more pronounced
at higher frequencies. The reconciliation of the NANOGrav results with the PPTA
bound is possible provided that the strings re-enter the horizon at adequately
late times. We consider an example of a realistic $SO(10)$ model incorporating
successful inflation driven by a gauge singlet real scalar field with a
Coleman-Weinberg potential. This model leads to the production of intermediate
scale topologically stable cosmic strings that survive inflation. We show
regions of the parameter space where the tension between NANOGrav and PPTA is
alleviated. Finally, we present an example in which both monopoles and strings
survive inflation with the above tension resolved.
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