Gravitational waves in an anomaly-induced inflation

2020

Prepared as invited review for La Rivista del Nuovo Cimento.

Progress of Theoretical Physics, 1997

We give the initial spectrum of quantized gravitational waves in the context of the onebubble open inHationary universe scenario. In determining the quantum state after the bubble nucleation, we adopt the prescription to require the analyticity of positive frequency functions in half of the Euclidian extension of the background 0(3, I)-symmetric spacetime. We find the spectrum is well behaved at the infrared limit and there appears no supercurvature mode. In the thin wall approximation, the explicit form of the spectrum of gravitational wave perturbations is calculated.

Physics Letters B, 1995

The gravitational waves (GW) background generated in a double inflationary model, with two scalar fields mutually interacting through gravity only, and its relative contribution T /S to large-angle temperature fluctuations of the relic microwave background are investigated in detail. The relation between T /S and the slope of the GW spectrum n T is shown to be a discriminative test between a slow-roll inflation driven by one scalar field and more complicated models. It is found that the GW amplitude is not exactly zero in minima of spectral oscillations, this property being an observational, in principle, manifestation of GW being in a squeezed vacuum state during inflation.

Journal of Cosmology and Astroparticle Physics, 2007

The generation of gravitational waves during inflation due to the non-linear coupling of scalar and tensor modes is discussed. Two methods describing gravitational wave perturbations are used and compared: a covariant and local approach, as well as a metric-based analysis based on the Bardeen formalism. An application to slow-roll inflation is also described.

Quintessential inflation explains both inflation and present accelerated expansion. In this model these two accelerated expansion is driven by a single scalar field. We construct a model based on an exponential potential. We consider two kinds of reheating process. One is the ordinary reheating in quintessential inflation, using gravitational particle creation. The other is the instant preheating which is much more effective. We calculate the relic gravitational waves produced during inflation in our model. We find that the spectrum of the gravitational waves is quite sensitive to the reheating process. Conversely, the detection or non-detection of primordial gravitational waves at ∼100MHz would have profound implications for the inflationary cosmology.

Physical Review D, 1993

We investigate models of 'intermediate' inflation, where the scale factor a(t) grows as a(t) = exp(At f), 0 < f < 1, A constant. These solutions arise as exact analytic solutions for a given class of potentials for the inflaton φ. For a simpler class of potentials falling off as a power of φ they arise as slow-roll solutions, and in particular they include, for f = 2/3, the class of potentials which give the Harrison-Zel'dovich spectrum. The perturbation spectral index n can be greater than unity on astrophysical scales. It is also possible to generate substantial gravitational waves while keeping the scalar spectrum close to scale-invariance; this latter possibility performs well when confronted with most observational data.

Physics Letters B, 2016

The inflationary paradigm is an important cornerstone of the concordance cosmological model. However, standard inflation cannot fully address the transition from an early homogeneous and isotropic stage, to another one lacking such symmetries corresponding to our present universe. In previous works, a self-induced collapse of the wave function has been suggested as the missing ingredient of inflation. Most of the analysis regarding the collapse hypothesis has been solely focused on the characteristics of the spectrum associated to scalar perturbations, and within a semiclassical gravity framework. In this Letter, working in terms of a joint metric-matter quantization for inflation, we calculate, for the first time, the tensor power spectrum and the tensor-to-scalar ratio corresponding to the amplitude of primordial gravitational waves resulting from considering a generic self-induced collapse.

International Journal of Modern Physics D, 2023

We investigate the effect of the cuspiness of scalar potentials on the production of gravitational waves during oscillon formation after inflation. We consider a more general form of potentials with a mass parameter M, which reproduce cuspy potentials for fields much larger than M and smooth potentials in the opposite limit. For cuspy potentials, nonsmooth oscillations of the inflaton induce an amplification of the inflaton fluctuations at the bottom of the potential, so that oscillons copiously form, which leads to a significant stochastic gravitational wave background with a double-peak spectrum. By varying the parameter M, we find that cuspy potentials yield stronger signals of gravitational waves and the generation of gravitational waves disappears for smooth potentials. Moreover, we calculate the equation of state after inflation and find the presence of a quasimatter-dominated stage right before the transition to the radiationdominated stage.

Journal of Cosmology and Astroparticle Physics, 2012

Measuring the primordial power spectrum on small scales is a powerful tool in inflation model building, yet constraints from Cosmic Microwave Background measurements alone are insufficient to place bounds stringent enough to be appreciably effective. For the very small scale spectrum, those which subtend angles of less than 0.3 degrees on the sky, an upper bound can be extracted from the astrophysical constraints on the possible production of primordial black holes in the early universe. A recently discovered observational by-product of an enhanced power spectrum on small scales, induced gravitational waves, have been shown to be within the range of proposed space based gravitational wave detectors; such as NASA's LISA and BBO detectors, and the Japanese DECIGO detector. In this paper we explore the impact such a detection would have on models of inflation known to lead to an enhanced power spectrum on small scales, namely the Hilltop-type and running mass models. We find that the Hilltop-type model can produce observable induced gravitational waves within the range of BBO and DECIGO for integral and fractional powers of the potential within a reasonable number of e−folds. We also find that the running mass model can produce a spectrum within the range of these detectors, but require that inflation terminates after an unreasonably small number of e−folds. Finally, we argue that if the thermal history of the Universe were to accomodate such a small number of e−folds the Running Mass Model can produce Primordial Black Holes within a mass range compatible with Dark Matter, i.e. within a mass range 10 20 g M BH 10 27 g.

Physical Review D, 2007

Preheating after inflation involves large, time-dependent field inhomogeneities, which act as a classical source of gravitational radiation. The resulting spectrum might be probed by direct detection experiments if inflation occurs at a low enough energy scale. In this paper, we develop a theory and algorithm to calculate, analytically and numerically, the spectrum of energy density in gravitational waves produced from an inhomogeneous background of stochastic scalar fields in an expanding universe. We derive some generic analytical results for the emission of gravity waves by stochastic media of random fields, which can test the validity/accuracy of numerical calculations. We contrast our method with other numerical methods in the literature, and then we apply it to preheating after chaotic inflation. In this case, we are able to check analytically our numerical results, which differ significantly from previous works. We discuss how the gravity wave spectrum builds up with time and find that the amplitude and the frequency of its peak depend in a relatively simple way on the characteristic spatial scale amplified during preheating. We then estimate the peak frequency and amplitude of the spectrum produced in two models of preheating after hybrid inflation, which for some parameters may be relevant for gravity wave interferometric experiments.