Probing The Early Universe Cosmology With NANOGrav: Possibilities and Limitations

Abstract

A stochastic gravitational wave background is a prediction of a number of astrophysical and cosmological phenomena including early Universe Cosmology. Recently, the NANOGrav Collaboration reported conclusive evidence for a stochastic gravitational-wave background. We analyze the NANOGrav signal assuming it is of primordial origin including the reheating phase. We use the latest measurements from NANOGrav to constrain the Universe's reheating equation of state $w_{re}$ the reheating temperature, $T_{re}$, the tensor to scalar ratio $r$, and the tensor tilt $n_t$. Assuming the constant equation of state $w_{re}$ responsible for reheating phase, we find preference for instant reheating, $w_{re}=0.36_{-0.28}^{+0.15}$, and a very blue tilt $n_t=1.94_{-0.88}^{+0.43}$. We find a degeneracy between the tensor to scalar ratio $r$ and $T_{re}$ and suggest ways to break this degeneracy. In all cases where the reheating temperature is constrained, it is constrained to be very low with $T_{re}\le 10^{5}GeV$. We further find that a scale-invariant spectrum as suggested by inflation implies a stiff equation of state $w_{re}=19/3$. If extrapolated, the blue-tilted primordial spectrum that agrees with the NANOGrav signal at corresponding frequencies is incompatible with the LIGO bound. This incompatibility is another challenge for connecting NANOGrav with the primordial spectrum. We discuss a number of ways to circumvent this issue. We split the spectrum into a sum of astrophysical and primordial spectra and constrain the astrophysical and primordial components using NANOGrav data and the LIGO bound. In another attempt, we use the same data and constrain the running of the spectrum. Any of these or a combination of such methods can be used to reconcile the NANOGrav data and the LIGO bound with the primordial power spectrum.

arXiv comment13 pages, 5 figures, 3 tables, reference added, figure changed

References in corpus (59)

• The Ekpyrotic Universe: Colliding Branes and the Origin of the Hot Big Bang
• The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background
• Search for an isotropic gravitational-wave background with the Parkes Pulsar Timing Array
• Searching for the nano-Hertz stochastic gravitational wave background with the Chinese Pulsar Timing Array Data Release I
• The second data release from the European Pulsar Timing Array III. Search for gravitational wave signals
• BICEP / Keck XIII: Improved Constraints on Primordial Gravitational Waves using Planck, WMAP, and BICEP/Keck Observations through the 2018 Observing Season
• Cosmological Backgrounds of Gravitational Waves
• The NANOGrav 15-year Data Set: Search for Signals from New Physics
• The NANOGrav 12.5-year Data Set: Search For An Isotropic Stochastic Gravitational-Wave Background
• Cobaya: Code for Bayesian Analysis of hierarchical physical models
• G-inflation: inflation driven by the Galileon field
• Upper Limits on the Isotropic Gravitational-Wave Background from Advanced LIGO's and Advanced Virgo's Third Observing Run
• Relativistic second-order perturbations of the Einstein-de Sitter Universe
• The NANOGrav 15-year Data Set: Constraints on Supermassive Black Hole Binaries from the Gravitational Wave Background
• The NANOGrav 15-year Data Set: Observations and Timing of 68 Millisecond Pulsars
• A Critical Review of Classical Bouncing Cosmologies
• The International Pulsar Timing Array second data release: Search for an isotropic Gravitational Wave Background
• On the evidence for a common-spectrum process in the search for the nanohertz gravitational-wave background with the Parkes Pulsar Timing Array
• Gauge Field Production in Axion Inflation: Consequences for Monodromy, non-Gaussianity in the CMB, and Gravitational Waves at Interferometers
• Particle production during inflation and gravitational waves detectable by ground-based interferometers
• Reheating constraints to inflationary models
• Common-red-signal analysis with 24-yr high-precision timing of the European Pulsar Timing Array: Inferences in the stochastic gravitational-wave background search
• A new cosmic microwave background constraint to primordial gravitational waves
• Implications of the NANOGrav results for inflation
• Relating gravitational wave constraints from primordial nucleosynthesis, pulsar timing, laser interferometers, and the CMB: implications for the early universe
• Inflationary interpretation of the stochastic gravitational wave background signal detected by pulsar timing array experiments
• Observing the Inflationary Reheating
• Primordial gravitational waves from NANOGrav: a broken power-law approach
• The gravitational-wave background null hypothesis: Characterizing noise in millisecond pulsar arrival times with the Parkes Pulsar Timing Array
• The NANOGrav 15-year Data Set: Bayesian Limits on Gravitational Waves from Individual Supermassive Black Hole Binaries
• The NANOGrav 15-Year Data Set: Detector Characterization and Noise Budget
• A Single Field Inflation Model with Large Local Non-Gaussianity
• Phantom Inflation and Primordial Perturbation Spectrum
• Adding helicity to inflationary magnetogenesis
• Higher Curvature Corrections to Primordial Fluctuations in Slow-roll Inflation
• Blue Tensor Spectrum from Particle Production during Inflation
• Blue-tilted Tensor Spectrum and Thermal History of the Universe
• New Sources of Gravitational Waves during Inflation
• The second data release from the European Pulsar Timing Array II. Customised pulsar noise models for spatially correlated gravitational waves
• Enhancing Inflationary Tensor Modes through Spectator Fields
• Elastic Inflation
• Updated Constraints and Forecasts on Primordial Tensor Modes
• The challenge of ruling out inflation via the primordial graviton background
• Gravitational wave research using pulsar timing arrays
• Observational implications of mattergenesis during inflation
• Constraints on Scalar and Tensor spectra from $N_{eff}$
• On the possibility of blue tensor spectrum within single field inflation
• Gravitational wave signal from massive gravity
• Rapid field excursions and the inflationary tensor spectrum
• Detecting relic gravitational radiation from string cosmology with LIGO
• Inflation and Alternatives with Blue Tensor Spectra
• Towards a reliable calculation of relic radiation from primordial gravitational waves
• Gravitational Waves in Bouncing Cosmologies from Gauge Field Production
• Nanohertz gravitational waves from NEC violation in the early universe
• Blue running of the primordial tensor spectrum
• Revisiting slow-roll dynamics and the tensor tilt in general single-field inflation
• Massive Graviton on a Spatial Condensate
• Sourced fluctuations in generic slow contraction
• Sourced Scalar Fluctuations in Bouncing Cosmology

Cited by in corpus (17)

• Broken blue-tilted inflationary gravitational waves: a joint analysis of NANOGrav 15-year and BICEP/Keck 2018 data
• Realisation of the ultra-slow roll phase in Galileon inflation and PBH overproduction
• Bounds on Ultralight Dark Matter from NANOGrav
• Search for Non-Tensorial Gravitational-Wave Backgrounds in the NANOGrav 15-Year Data Set
• Enhancement of gravitational waves at Q-ball decay including non-linear density perturbations
• Null energy condition violation during inflation and pulsar timing array observations
• Constraints on holographic QCD phase transitions from PTA observations
• Obviating PBH overproduction for SIGWs generated by Pulsar Timing Arrays in loop corrected EFT of bounce
• Prospects for Taiji to detect a gravitational-wave background from cosmic strings
• Beyond the Hellings-Downs curve: Non-Einsteinian gravitational waves in pulsar timing array correlations
• Correlations for an anisotropic polarized stochastic gravitational wave background in pulsar timing arrays
• Testing scale-invariant inflation against cosmological data
• Untangling PBH overproduction in $w$-SIGWs generated by Pulsar Timing Arrays for MST-EFT of single field inflation
• Gravitational-wave background in bouncing models from semi-classical, quantum and string gravity
• Climbing over the potential barrier during inflation via null energy condition violation
• Purely quadratic non-Gaussianity from tachyonic instability: Primordial black holes and scalar-induced gravitational waves
• Testing No slip model with pulsar timing arrays: NANOGrav and IPTA