Gravitational wave generation in power-law inflationary models

We investigate the generation of gravitational waves in power-law inflationary models. The energy spectrum of the gravitational waves is calculated using the method of continuous Bogoliubov coefficients. We show that, by looking at the interval of frequencies between 10⁻⁵ and 10⁵ Hz and also at the GHz range, important information can be obtained, both about the inflationary period itself and about the thermalization regime between the end of inflation and the beginning of the radiation-dominated era. We thus deem the development of gravitational wave detectors, covering the MHz/GHz range of frequencies, to be an important task for the future.     

Search for a stochastic background of 100-MHz gravitational waves with laser interferometers

This Letter reports the results of a search for a stochastic background of gravitational waves (GW) at 100 MHz by laser interferometry. We have developed a GW detector, which is a pair of 75-cm baseline synchronous recycling (resonant recycling) interferometers. Each interferometer has a strain sensitivity of approximately 10;{-16} Hz;{-1/2} at 100 MHz. By cross-correlating the outputs of the two interferometers within 1000 seconds, we found h{100};{2}Omega_{gw}<6 x 10;{25} to be an upper limit on the energy density spectrum of the GW background in a 2-kHz bandwidth around 100 MHz, where a flat spectrum is assumed.     

Gravitational waves generated during inflation from a 5D vacuum theory of gravity in a de Sitter expansion

In this Letter we study the generation of gravitational waves during inflation from a 5D vacuum theory of gravity. Within this formalism, on an effective 4D de Sitter background, we recover the typical results obtained with 4D inflationary theory in general relativity, for the amplitude of gravitational waves generated during inflation. We also obtain a range of values for the amplitude of tensor to scalar ratio which is in agreement with COBE observations.     

Stochastic background of gravitational waves from hybrid preheating

The process of reheating the Universe after hybrid inflation is extremely violent. It proceeds through the nucleation and subsequent collision of large concentrations of energy density in bubblelike structures, which generate a significant fraction of energy in the form of gravitational waves. We study the power spectrum of the stochastic background of gravitational waves produced at reheating after hybrid inflation. We find that the amplitude could be significant for high-scale models, although the typical frequencies are well beyond what could be reached by planned gravitational wave observatories. On the other hand, low-scale models could still produce a detectable stochastic background at frequencies accessible to those detectors. The discovery of such a background would open a new window into the very early Universe.     

Successful supersymmetric inflation

We reconsider the problems of cosmological inflation in effective supergravity theories. A singlet field in a hidden sector is demonstrated to yield an acceptable inflationary potential, without fine tuning. In the simplest such model, the requirement of generating the microwave background anisotropy measured by COBE fixes the inflationary scale to be about 10¹⁴ GeV, implying a reheat temperature of order 10⁵ GeV. This is low enough to solve gravitino problem but high enough to allow baryogenesis after inflation. Such consistency requires that the generation of gravitational waves be negligible and that the spectrum of scalar density perturbations depart significantly from scale invariance, thus improving the fit to large-scale structure in an universe dominated by cold dark matter. We also consider the problems associated with gravitino production through inflaton decay and with other weakly coupled fields such as the moduli encountered in (compactified) string theories.     

Non-minimal Coupling of the Higgs Boson to Curvature in an Inflationary Universe

In the absence of new physics around \(10^{10}\) GeV, the electroweak vacuum is at best metastable. This represents a major challenge for high scale inflationary models as, during the early rapid expansion of the universe, it seems difficult to understand how the Higgs vacuum would not decay to the true lower vacuum of the theory with catastrophic consequences if inflation took place at a scale above \(10^{10}\) GeV. In this paper we show that the non-minimal coupling of the Higgs boson to curvature could solve this problem by generating a direct coupling of the Higgs boson to the inflationary potential thereby stabilizing the electroweak vacuum. For specific values of the Higgs field initial condition and of its non-minimal coupling, inflation can drive the Higgs field to the electroweak vacuum quickly during inflation.     

Towards the bounce inflationary gravitational wave

In the bounce inflation scenario, the inflation is singularity-free, while the advantages of inflation are preserved. We analytically calculate the power spectrum of its primordial gravitational waves (GWs), and show a universal result including the physics of the bounce phase. The spectrum acquires a cutoff at large scale, while the oscillation around the cutoff scale is quite drastic, which is determined by the details of bounce. Our work highlights that the primordial GWs at large scale may encode the physics of the bounce ever happened at about \({\sim }60\) efolds before inflation.     

Test the mergers of the primordial black holes by high frequency gravitational-wave detector

The black hole could have a primordial origin if its mass is less than \(1M_\odot \). The mergers of these black hole binaries generate stochastic gravitational-wave background (SGWB). We investigate the SGWB in high frequency band \(10^{8}\)–\(10^{10}\,\mathrm {Hz}\). It can be detected by high frequency gravitational-wave detector. Energy density spectrum and amplitude of the SGWB are derived. The upper limit of the energy density spectrum is around \(10^{-7}\). Also, the upper limit of the amplitude ranges from \(10^{-31.5}\) to \(10^{-29.5}\). The fluctuation of spacetime origin from gravitational wave could give a fluctuation of the background electromagnetic field in a high frequency gravitational-wave detector. The signal photon flux generated by the SGWB in the high frequency band \(10^{8}\)–\(10^{10}\,\mathrm {Hz}\) is derived, which ranges from 1 to \(10^2\,\mathrm {s^{-1}}\). The comparison between the signal photon flux generated by relic gravitational waves (RGWs) and the SGWB is also discussed in this paper. It is shown that the signal photon flux generated by the RGW, which is predicted by the canonical single-field slow-roll inflation models, is sufficiently lower than the one generated by the SGWB in the high frequency band \(10^{8}\)–\(10^{10}\,\mathrm {Hz}\). Our results indicate that the SGWB in the high frequency band \(10^{8}\)–\(10^{10}\,\mathrm {Hz}\) is more likely to be detected by the high frequency gravitational-wave detector.     

Cosmic 21 cm delensing of microwave background polarization and the minimum detectable energy scale of inflation

We propose a new method for removing gravitational lensing from maps of cosmic microwave background (CMB) polarization anisotropies. Using observations of anisotropies or structures in the cosmic 21 cm radiation, emitted or absorbed by neutral hydrogen atoms at redshifts 10 to 200, the CMB can be delensed. We find this method could allow CMB experiments to have increased sensitivity to a background of inflationary gravitational waves (IGWs) compared to methods relying on the CMB alone and may constrain models of inflation which were heretofore considered to have undetectable IGW amplitudes.     

Quantum gravitational contributions to the cosmic microwave background anisotropy spectrum

We derive the primordial power spectrum of density fluctuations in the framework of quantum cosmology. For this purpose we perform a Born-Oppenheimer approximation to the Wheeler-DeWitt equation for an inflationary universe with a scalar field. In this way, we first recover the scale-invariant power spectrum that is found as an approximation in the simplest inflationary models. We then obtain quantum gravitational corrections to this spectrum and discuss whether they lead to measurable signatures in the cosmic microwave background anisotropy spectrum. The nonobservation so far of such corrections translates into an upper bound on the energy scale of inflation.     

Induced-gravity GUT-scale Higgs inflation in supergravity

Models of induced-gravity inflation are formulated within Supergravity employing as inflaton the Higgs field which leads to a spontaneous breaking of a \(U(1)_{B-L}\) symmetry at \(M_\mathrm{GUT}=2\cdot 10^{16}~{\mathrm{GeV}}\). We use a renormalizable superpotential, fixed by a U(1) R symmetry, and Kähler potentials which exhibit a quadratic non-minimal coupling to gravity with or without an independent kinetic mixing in the inflaton sector. In both cases we find inflationary solutions of Starobinsky type whereas in the latter case, others (more marginal) which resemble those of linear inflation arise too. In all cases the inflaton mass is predicted to be of the order of \(10^{13}~{\mathrm{GeV}}\). Extending the superpotential of the model with suitable terms, we show how the MSSM \(\mu \) parameter can be generated. Also, non-thermal leptogenesis can be successfully realized, provided that the gravitino is heavier than about \(10~{\mathrm{TeV}}\).     

Self-accelerated Universe Induced by Repulsive Effects as an Alternative to Dark Energy and Modified Gravities

The existence of current–time universe’s acceleration is usually modeled by means of two main strategies. The first makes use of a dark energy barotropic fluid entering by hand the energy–momentum tensor of Einstein’s theory. The second lies on extending the Hilbert–Einstein action giving rise to the class of extended theories of gravity. In this work, we propose a third approach, derived as an intrinsic geometrical effect of space–time, which provides repulsive regions under certain circumstances. We demonstrate that the effects of repulsive gravity naturally emerge in the field of a homogeneous and isotropic universe. To this end, we use an invariant definition of repulsive gravity based upon the behavior of the curvature eigenvalues. Moreover, we show that repulsive gravity counterbalances the standard gravitational attraction influencing both late and early times of the universe evolution. This phenomenon leads to the present speed up and to the fast expansion due to the inflationary epoch. In so doing, we are able to unify both dark energy and inflation in a single scheme, showing that the universe changes its dynamics when \({\ddot{H}\over H}=-2 \dot{H}\), at the repulsion onset time where this condition is satisfied. Further, we argue that the spatial scalar curvature can be taken as vanishing because it does not affect at all the emergence of repulsive gravity. We check the goodness of our approach through two cosmological fits involving the most recent union 2.1 supernova compilation.     

The signal photon flux,background photons and shot noise in electromagnetic response of high-frequency relic gravitational waves

On the basis of the electromagnetic response of high frequency relic gravitational waves (HFRGWs), we research on more accurate calculation of signal (i.e. transverse perturbative photon flux (PPF)) and background photons flux (BPF) in the sycro-resonance electromagnetic system, which consists of Gaussian beam (GB), a static magnetic field and fractal membranes. According to the relationship between frequency of gravitational waves and its dimensionless amplitude, we focus on the HFRGWs with ν _g  = 2.9 GHz, h ~ 10^?30 in the pre-big bang and quintessential inflationary models. The results show the peak value of the transverse BPF (~ 10²⁰ s^?1) is around |x| = 0.08 m, where |x| is the transverse distance to the longitudinal symmetrical surface of the GB, while the maximum transverse PPF always appears at x = 0 (\({N^{(1)}_{x} \sim 2.60\times10^{2}\,{\rm s}^{-1}}\) with the optimal phase difference between the GB and the resonant component of the HFRGWs δ = (n + 0.9)π, n = 0, 1, 2 . . .). However, the observable PPF should be ~ 1.19 × 10² s^?1 because of the stochastic nature of the HFRGWs’ phase. Since the decay speed of BPF is much quicker than PPF, it is hopeful to figure out the signal in some optimal regions. Moreover, we compare the decay speed of BPF and PPF in nature mode, and find the threshold value of x where PPF exceeds to BPF. It demonstrates that the limitation of our detection sensitivity comes from the strength of PPF rather than swamping by BPF. On the other hand, with the fractal membrane, the comparison between BPF and PPF provides the optimal detection area \({x\in[0.28,1]}\) m. In addition, through the calculation of shot noise and conservative estimation, we find that our sensitivity is h = 10^?26 in 4 months signal accumulate time.     

A special form of electrodynamical response to a gravitational wave：outgoing and imploding photon fluxes

We have investigated the interaction of an electromagnetic (EM) wave with a standing gravitational wave (GW) in an external static magnetic field,and obtained concrete forms of first-order perturbative EM energy fluxes.Unlike the propagating properties of the “left-circular” and “right-circular” waves of the tangential perturbative energy fluxes around the symmetrical axis,the radial perturbative energy fluxes are expressed as the outgoing and imploding waves to the symmetrical axis.We also examine several physical examples and show that this effect can produce very small but nonvanishing radial perturbative photon fluxes.This may be useful for EM detection of the high-frequency relic GWs of the GHz region in quintessential inflationary models.     

Leptogenesis from gravity waves in models of inflation

We present a new mechanism for creating the observed cosmic matter-antimatter asymmetry which satisfies all three Sakharov conditions from one common thread, gravitational waves. We generate lepton number through the gravitational anomaly in the lepton number current. The source term comes from elliptically polarized gravity waves that are produced during inflation if the inflaton field contains a CP-odd component. The amount of matter asymmetry generated in our model can be of realistic size for the parameters within the range of some inflationary scenarios and grand unified theories.     

Gravitational waves from a supercooled electroweak phase transition and their detection with pulsar timing arrays

We investigate the properties of a stochastic gravitational wave background produced by a first-order electroweak phase transition in the regime of extreme supercooling. We study a scenario whereby the percolation temperature that signifies the completion of the transition, \(T_\mathrm{p}\), is as low as a few MeV (nucleosynthesis temperature), while most of the true vacuum bubbles are formed much earlier at the nucleation temperature, \(T_\mathrm{n}\sim 50\) GeV. This implies that the gravitational wave spectrum is mainly produced by the collisions of large bubbles and characterised by a large amplitude and a peak frequency as low as \(f \sim 10^{-9}{-}10^{-7}\) Hz. We show that such a scenario can occur in (but not limited to) a model based on a non-linear realisation of the electroweak gauge group, so that the Higgs vacuum configuration is altered by a cubic coupling. In order to carefully quantify the evolution of the phase transition of this model over such a wide temperature range we go beyond the usual fast transition approximation, taking into account the expansion of the Universe as well as the behaviour of the nucleation probability at low temperatures. Our computation shows that there exists a range of parameters for which the gravitational wave spectrum lies at the edge between the exclusion limits of current pulsar timing array experiments and the detection band of the future Square Kilometre Array observatory.     

Modular thermal inflation without slow-roll approximation

We study an inflationary scenario where thermal inflation is followed by fast-roll inflation. This is a rather generic possibility based on the effective potentials of spontaneous symmetry breaking in the context of particle physics models. We show that a large enough expansion could be achieved to solve cosmological problems. However, the power spectrum of primordial density perturbations from the quantum fluctuations in the inflaton field is not scale invariant and thus inconsistent with observations. Using the curvaton mechanism instead, we can obtain a nearly scale invariant spectrum, provided that the inflationary energy scale is sufficiently low to have long enough fast-roll inflation to dilute the perturbations produced by the inflaton fluctuations.     

Towards the Graceful Exit From the Anomaly-Induced Inflation

The method for the effective action for massive quantum fields in curved space-time is based on the conformal representation of the fields action and consequent integration of the conformal anomaly. As a relevant cosmological application, we find that if we take the masses of the fields into account, then the stable anomaly-induced inflation slows down due to the effect of massive fermions. In supersymmetric theories this mechanism can be specially efficient, for it may naturally provide the graceful exit from the inflationary to the FLRW phase. Taking the SUSY breaking into account, the anomaly-induced inflation could be free of the well-known difficulties with the initial data and also with the amplitude of the gravitational waves.     

Plasma suppression of large scale structure formation in the universe

We point out that during the reionization epoch of the cosmic history, the plasma collective effect among the ordinary matter would suppress the large scale structure formation. The imperfect Debye shielding at finite temperature would induce an electrostatic pressure which, working together with the thermal pressure, would counter the gravitational collapse. As a result, the effective Jeans length, lambda[over ]_{J} is increased by a factor lambda[over ]_{J}/lambda_{J}=sqrt[8/5], relative to the conventional one. For scales smaller than the effective Jeans scale the plasma would oscillate at the ion-acoustic frequency. The modes that would be influenced by this effect lie roughly in the range 0.5h Mpc;{-1}相似文献   

Production of spin 3/2 particles from vacuum fluctuations

We study the production of spin 3/2 particles in homogeneous scalar and gravitational backgrounds using the mode-mixing Bogolyubov method. Considering only the helicity +/-3/2 states, we can reduce the problem to a standard Dirac fermion calculation and apply the standard techniques in a straightforward way. As an example we consider a specific supergravity inflationary model and calculate the spectrum of gravitinos created during preheating at the end of inflation.