1,721,355 research outputs found
A cosmological bound on the thermal axion mass
No full textRelic thermal axions could play the role of an extra hot dark matter component in cosmological structure formation theories. By combining the most recent observational data we improve previous cosmological bounds on the axion mass m(a) in the so-called hadronic axion window
Probing the inflationary background of gravitational waves from large to small scales
Full text linkThe detection of Primordial Gravitational Waves (PGWs) is one of the most important goals of modern cosmology since PGWs can both provide substantial evidence for primordial inflation and shed light on its physical nature. Small scale experiments on gravitational waves such as LIGO/VIRGO and, in future, LISA and Einstein Telescope (ET), being sensitive to the stochastic background of gravitational waves, can be used together with the CMB data to constrain the inflationary parameters. In performing these analyses the primordial tensor spectrum is usually parametrized with a power law that includes only the amplitude and a scale independent tilt. In this paper, we investigate the robustness of assuming the tensor tilt as scale independent. We show that due to the huge difference in the scales probed by CMB and GWs data, even a small scale dependence can remarkably affect the shape of the primordial spectrum possibly breaking the power-law assumption. When the non-linear corrections are considered the final constraints can be significantly changed. We also study the scale dependence in two different physical models of inflation providing an example of negligible scale dependence and an example of non-negligible scale dependence
Searching for integrated Sachs Wolfe effect beyond temperature anisotropies: CMB E-mode polarization galaxy cross-correlation
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When did cosmic acceleration start?
No full textA precise determination, and comparison, of the epoch of the onset of cosmic acceleration, at redshift z(acc), and of dark energy domination, at z(eq), provides an interesting measure with which to parametrize dark energy models. By combining several cosmological data sets, we place constraints on the redshift and age of cosmological acceleration. For a Lambda CDM model, we find the constraint z(acc)=0.76 +/- 0.10 at 95% C.L., occurring 6.7 +/- 0.4 Gyr ago. Allowing a constant equation of state but different from -1 changes the constraint to z(acc)=0.81 +/- 0.12 (6.9 +/- 0.5 Gyr ago), while dynamical models markedly increase the error on the constraint z(acc)=0.81 +/- 0.30 (6.8 +/- 1.4 Gyr ago). Unified dark energy models such as silent quartessence yield z(acc)=0.8 +/- 0.16 (6.8 +/- 0.6 Gyr ago). Interestingly, we find that the best fit z(acc) and z(eq) are remarkably insensitive to both the cosmological data sets and theoretical dark energy models considered
WMAP-normalized inflationary model predictions and the search for primordial gravitational waves with direct detection experiments
No full textIn addition to density perturbations, inflationary models of the early Universe generally predict a stochastic background of gravitational waves or tensor fluctuations. By making use of the inflationary flow approach for single field models and fitting the models with Monte Carlo techniques to cosmic microwave background (CMB) data from the Wilkinson Microwave Anisotropy Probe (WMAP), we discuss the expected properties of the gravitational wave background from inflation at scales corresponding to direct detection experiments with laser interferometers in space. We complement the Monte Carlo numerical calculations by including predictions expected under several classes of analytical inflationary models. We find that an improved version of big bang observer (BBO-grand) can be used to detect a gravitational wave background at 0.1 Hz with a corresponding CMB tensor-to-scalar ratio above 10(-4). Even if the CMB tensor-to-scalar ratio were to be above 10(-2), we suggest that BBO-grand will be useful to study inflationary models as the standard version of BBO, with a sensitivity to a stochastic gravitational wave background Omega(GW)h(2)> 10(-17), will only allow a marginal detection of the amplitude while leaving the tensor spectral index at 0.1 Hz unconstrained. Also, inflationary models with a large tensor-to-scalar ratio predict a substantial negative tensor spectral index such that the gravitational wave amplitude is damped at direct detection frequencies. We also discuss the extent to which CMB measurements can be used to predict the gravitational wave background amplitude in a direct detection experiment and how any measurement of the amplitude and the spectral tilt of the gravitational wave background at direct detection frequencies together with the CMB tensor-to-scalar ratio can be used to establish slow-roll inflation
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