Constraining models of inflationary magnetogenesis with NANOGrav data

Abstract

Generation of magnetic field during inflation can explain its presence over a wide range of scales in the Universe. In Ref. [1], we proposed a model to generate these fields during inflation. These fields have nonzero anisotropic stress which lead to the generation of a stochastic background of gravitational waves (GW) in the early universe. Here we show that for a scenario of magnetogenesis where reheating takes place around QCD epoch, this stochastic GW background lies in the 95% confidence region of the GW signal probed by NANOGrav collaboration. This is the case when the generated electromagnetic field (EM) energy density is 3 − 10% of the background energy density at the end of reheating. For this case, the values of magnetic field strength B0 ∼ (3.8 − 6.9) × 10 −11 G and its coherence length ∼ 30 kpc at the present epoch. These values are for the models in which EM fields are of nonhelical nature. For the helical nature of the fields, these values are B0 ∼ (1.1 − 1.9) × 10 −9 G and its coherence length ∼ 0.8 Mpc.

NANOGrav signal and LIGO-Virgo primordial black holes from the Higgs field

“…(For other explanations for the sources of the NANOGrav signal, see refs. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24].) The nanohertz frequencies of SIGWs constrain the masses of PBHs to stellar mass, and these stellar mass PBHs, on the other hand, may be the sources of the GWs detected by the Laser Interferometer Gravitational Wave Observatory (LIGO) Scientific Collaboration and the Virgo Collaboration [25][26][27][28][29][30][31][32][33][34][35][36][37][38].…”

Low frequency tail of gravitational wave spectra from hydromagnetic turbulence

“…Recently, various pulsar timing arrays [17][18][19][20] have reported evidence for the presence of a common spectrum process across analyzed pulsars in the search of the presence of an isotropic stochastic GW background. This evidence has been used to constrain the strength and correlation length of the magnetic fields generated at the QCD epoch [21][22][23]. However, the presence of a quadrupolar spatial correlation [24], a characteristics of a GW background, is yet to be claimed.…”

Constraining gravitational wave propagation using pulsar timing array correlations

“…As the CMB is host to physics during last scattering, the SGWB is host to a variety of sources tied to the early Universe, such as supermassive black hole binary coalescences [6][7][8], and more exotic phenomena like cosmic strings [9,10], phase transitions [11,12], and primordial black holes [13,14], among others [15,16]. PTA astronomy caters to such exciting physics that come with the SGWB.…”