Constraint on the early Universe by relic gravitational waves: From pulsar timing observations

TY - JOUR

T1 - Constraint on the early Universe by relic gravitational waves

T2 - From pulsar timing observations

AU - Zhao, Wen

PY - 2011/5/10

Y1 - 2011/5/10

N2 - Recent pulsar timing observations by the Parkers Pulsar Timing Array (PPTA) and European Pulsar Timing Array (EPTA) teams obtained the constraint on the relic gravitational waves at the frequency f*=1/yr, which provides the opportunity to constrain H*, the Hubble parameter, when these waves crossed the horizon during inflation. In this paper, we investigate this constraint by considering the general scenario for the early Universe: we assume that the effective (average) equation-of-state w before the big bang nucleosynthesis stage is a free parameter. In the standard hot big-bang scenario with w=1/3, we find that the current PPTA result follows a bound H*≤1.15×10-1mPl, and the EPTA result follows H*≤6.92×10-2mPl. We also find that these bounds become much tighter in the nonstandard scenarios with w>1/3. When w=1, the bounds become H*≤5. 89×10-3mPl for the current PPTA and H *≤3.39×10-3mPl for the current EPTA. In contrast, in the nonstandard scenario with w=0, the bound becomes H*≤7.76mPl for the current PPTA.

AB - Recent pulsar timing observations by the Parkers Pulsar Timing Array (PPTA) and European Pulsar Timing Array (EPTA) teams obtained the constraint on the relic gravitational waves at the frequency f*=1/yr, which provides the opportunity to constrain H*, the Hubble parameter, when these waves crossed the horizon during inflation. In this paper, we investigate this constraint by considering the general scenario for the early Universe: we assume that the effective (average) equation-of-state w before the big bang nucleosynthesis stage is a free parameter. In the standard hot big-bang scenario with w=1/3, we find that the current PPTA result follows a bound H*≤1.15×10-1mPl, and the EPTA result follows H*≤6.92×10-2mPl. We also find that these bounds become much tighter in the nonstandard scenarios with w>1/3. When w=1, the bounds become H*≤5. 89×10-3mPl for the current PPTA and H *≤3.39×10-3mPl for the current EPTA. In contrast, in the nonstandard scenario with w=0, the bound becomes H*≤7.76mPl for the current PPTA.

U2 - 10.1103/PhysRevD.83.104021

DO - 10.1103/PhysRevD.83.104021

M3 - Journal article

SN - 2470-0010

VL - 83

SP - 104021

JO - Physical Review D

JF - Physical Review D

IS - 10

ER -