Inflationary Spectrum Research Articles

Kähler potential braneworld inflation in supergravity after Planck 2015

We analyze the slow-roll mechanism in Randall–Sundrum II braneworld with a supersymmetric hybrid inflation model. We are interested in studying various inflationary spectrum perturbation parameters in two cases. The first is the minimal Kähler potential where the inflationary parameters depend on the number of [Formula: see text]-foldings [Formula: see text] as well as the brane tension [Formula: see text], such that we produce the central value of the spectral index [Formula: see text]. The second case concerns the nonminimal Kähler potential, where the inflationary parameters depend only on the brane tension. Also, the [Formula: see text]-problem is solved for natural coupling parameter values which is not realized in the standard case. In addition, for a suitable choice of brane tension value [Formula: see text], the perturbation spectrum is widely consistent with Planck data.

Smooth hybrid inflation on brane constrained by Planck data

It is shown that, in the supersymmetric smooth hybrid inflation model with the minimal Kähler potential, the spectral index ns is larger than 0.97 in the standard inflation. In this context, we study the smooth hybrid inflationary model in the framework of the Randall–Sundrum type-II braneworld model. We derive all known inflationary spectrum parameters which are widely consistent with Planck data for a particular choice of brane tension values λ especially for number of e-folds N = 50. We reproduce the central value of the scalar spectral index ns = 0.96 whereas the ratio r~(10-4-10-3). However, the running of the scalar spectral index [Formula: see text] is not excluded from the range given by the latest observational measurements.

MSSM braneworld inflation

We consider a Minimal Supersymmetric Standard Model (MSSM) inflation in the context of the Randall-Sundrum type-2 braneworld model. We apply the slow-roll approximations, in high-energy limit, to constraint various inflationary spectrum parameters in relation with recent WMAP9 data. We show that, for some values of the number of efolding N, the MSSM braneworld inflation provides the best fit results according to recent observations.

Perturbations in Chromo-Natural Inflation

Chromo-Natural Inflation is the first worked example of a model of inflation in which slow-roll inflation is achieved by “magnetic drift” as opposed to Hubble friction. In this work, we give an account of the perturbations at linear order in this model. Our analysis uncovers two novel phenomena. First, the amplitude of scalar curvature perturbations is not directly tied to the shape of the inflationary potential. This allows the theory to violate na¨ıve formulations of the Lyth bound. Second, the tensor sector of the theory is significantly altered from the usual case: the non-Abelian gauge field perturbations have a tensor degree of freedom. One chirality of the this tensor can be exponentially enhanced by a temporary instability near horizon crossing; this chiral instability exists because of the classical gauge field background, which violates parity. These tensor fluctuations of the gauge field also couple to gravitational waves at linear order in perturbation theory and source a chiral spectrum of gravitational waves. This spectrum can be exponentially enhanced over the usual inflationary spectrum due to the instability in the gauge sector. These new features cause the theory in its present form to be in significant tension with current observational data. This is because the new scalar physics leads to a significant reddening of the spectral tilt in the same region of parameter space where the exponential enhancement of the gravitational wave amplitude is small enough to satisfy current constraints on the tensor-to-scalar index. Hence, the model either predicts a spectral tilt that is too red, or it overproduces gravitational waves, or both.

TACHYONIC BRANEWORLD INFLATION AND OBSERVATIONS

We study various tachyonic inflationary spectrum perturbations in the context of the Randall–Sundrum type-2 braneworld model [L. Randall and R. Sundrum, Phys. Rev. Lett.83, 3370 (1999); Phys. Rev. Lett.83, 4690 (1999)]. We consider, in particular, the inverse power law potential [Formula: see text] of the tachyonic field in the high-energy and slow-roll approximations using the recent astronomical observations.

OBSERVATIONAL CONSTRAINTS ON D-TERM BRANEWORLD INFLATION

We consider a supersymmetric hybrid inflation in the framework of the Randall–Sundrum type-2 braneworld model. We derive an analytical expression for the effective scalar potential and find that the D-term dominates hybrid inflation process. We show that we can eliminate partially the fine tuning problem related to coupling constant λ of the potential and calculate the value of FI-term ξ according to recent WMAP7 observation data. We show also that some inflationary spectrum parameters, in particular, the ratio r and the running [Formula: see text] are widely consistent with WMAP7, BAO and H0 data.

SMOOTHED QUANTUM FLUCTUATIONS AND CMB OBSERVATIONS

In this paper, we investigate power spectrum of a smoothed scalar field. The smoothing leads to regularization of the UV divergences and can be related with the internal structure of the considered field or the space itself. We perform Gaussian smoothing to the quantum fluctuations generated during the phase of cosmic inflation. We study whether this effect can be probed observationally and conclude that the modifications of the power spectrum due to the smoothing on the Planck scale are negligible and far beyond the observational abilities. Subsequently, we investigate whether smoothing in any other form can be probed observationally. We introduce phenomenological smoothing factor e-k2σ2 to the inflationary spectrum and investigate its effects on the spectrum of CMB anisotropies and polarization. We show that smoothing can lead to suppression of high multipoles in the spectrum of the CMB. Based on seven years observations of WMAP satellite we indicate that the present scale of high multipoles suppression is constrained by σ < 3.19 Mpc (95% CL). This corresponds to the constraint σ < 100 μm at the end of inflation. Despite this value is far above the Planck scale, other processes of smoothing can be possibly studied with this constraint, as decoherence or diffusion of primordial perturbations.

Inflationary spectra and observations in loop quantum cosmology

We review some recent progress in the extraction of inflationary observables in loop quantum cosmology. Inverse-volume quantum corrections induce a growth of power in the large-scale cosmological spectra and are constrained by observations.

Novel Possibility of Nonstandard Statistics in the Inflationary Spectrum of Primordial Inhomogeneities

Inflation is considered one of the cornerstones of modern cosmology. However, the account of the origin of cosmic structure, as provided by the standard inflationary paradigm, is not fully satisfactory. The fundamental issue is the inability of the usual account to point out the physical mechanism responsible for generating the inhomogeneity and anisotropy of our Universe, starting from the exactly homogeneous and isotropic vacuum state associated with the early inflationary regime. We briefly review this issue here together with the proposal to address this shortcoming in terms of a dynamical collapse of the vacuum state of the inflaton field, which has been considered in previous works. The main goal of this manuscript is to discuss certain statistical aspects associated with the collapse and its implications in the primordial spectrum, particularly those connected with the possible appearance of a novel type of unusual correlations.

Formation of superdense dark matter lumps at the radiation-dominated cosmological stage

We study the process of superdense dark matter clump (DMC) formation at the radiation-dominated stage of the Universe. High-magnitude density perturbations that lead to DMC formation can be peaks in the inflationary perturbation spectrum or closed loops of cosmic strings. A model with superdense DMCs provides new opportunities for annihilation of particles having small annihilation cross-sections. Superdense DMCs can be detected by their tidal effect on gravitational wave detectors.

On Braneworld inflation models in light of WMAP7 data

We are interested on studying various inflationary spectrum perturbation parameters in the context of the Randall-Sandrum type 2 Braneworld model. We consider in particular three types of potentials. We apply the slow-roll approximation in the high energy limit to constraint the parameter potentials by confronting our results to recent WMAP7 observations. We show that, for some values of the e-folding number N, the monomial potential provides the best fit results to observations data.

Chaplygin gas braneworld inflation according to WMAP7 data

We consider a Chaplygin gas model with an exponential potential in framework of braneworld inflation. We apply the slow-roll approximation in the high-energy limit to derive various inflationary spectrum perturbation parameters. We show that the inflation observables depend only on the e-folding number N and the final value of the slow-roll parameter e(end). Whereas for small running of the scalar spectral index dns/dlnk, the inflation observables are in good agreement with recent WMAP7 data.

Observable effects of anisotropic bubble nucleation

Our universe may have formed via bubble nucleation in an eternally-inflating background. Furthermore, the background may have a compact dimension — the modulus of which tunnels out of a metastable minimum during bubble nucleation — which subsequently grows to become one of our three large spatial dimensions. Then the reduced symmetry of the background is equivalent to anisotropic initial conditions in our bubble universe. We compute the inflationary spectrum in such a scenario and, as a first step toward understanding the effects of anisotropy, project it onto spherical harmonics. The resulting spectrum exhibits anomalous multipole correlations, their relative amplitude set by the present curvature parameter, which appear to extend to arbitrarily large multipole moments. This raises the possibility of future detection, if slow-roll inflation does not last too long within our bubble. A full understanding of the observational signal must account for the effects of background anisotropy on photon free streaming, and is left to future work.

Observational hints on the Big Bounce

In this paper we study possible observational consequences of the bouncing cosmology. We consider a model where a phase of inflation is preceded by a cosmic bounce. While we consider in this paper only that the bounce is due to loop quantum gravity, most of the results presented here can be applied for different bouncing cosmologies. We concentrate on the scenario where the scalar field, as the result of contraction of the universe, is driven from the bottom of the potential well. The field is amplified, and finally the phase of the standard slow-roll inflation is realized. Such an evolution modifies the standard inflationary spectrum of perturbations by the additional oscillations and dampingon the large scales. We extract the parameters of the model from the observationsof the cosmic microwave background radiation. In particular, the value of inflaton mass is equal to m = (1.7±0.6)·1013 GeV. In our considerations we base on the seven years of observations made by the WMAP satellite. We propose the new observational consistency check forthe phase of slow-roll inflation. We investigate the conditions which have to be fulfilled to make the observations of the Big Bounce effects possible. We translate them to the requirements on the parameters of the model andthen put the observational constraints on the model. Based on assumption usually made in loop quantum cosmology, the Barbero-Immirzi parameter was shown to be constrained by γ < 1100 from the cosmological observations. We have compared the Big Bounce model with the standard Big Bang scenario and showed that the present observational data is not informative enough to distinguish these models.

Primordial perturbations from multifield inflation with nonminimal couplings

Realistic models of particle physics include many scalar fields. These fields generically have nonminimal couplings to the Ricci curvature scalar, either as part of a generalized Einstein theory or as necessary counterterms for renormalization in curved background spacetimes. We develop a gauge-invariant formalism for calculating primordial perturbations in models with multiple nonminimally coupled fields. We work in the Jordan frame (in which the nonminimal couplings remain explicit) and identify two distinct sources of entropy perturbations for such models. One set of entropy perturbations arises from interactions among the multiple fields. The second set arises from the presence of nonminimal couplings. Neither of these varieties of entropy perturbations will necessarily be suppressed in the long-wavelength limit, and hence they can amplify the curvature perturbation $\ensuremath{\zeta}$, even for modes that have crossed outside the Hubble radius. Models that overproduce long-wavelength entropy perturbations endanger the close fit between predicted inflationary spectra and empirical observations.

Punctuated inflation and the low CMB multipoles

We investigate inflationary scenarios driven by a class of potentials which are similar in form to those that arise in certain minimal supersymmetric extensions of the standard model. We find that these potentials allow a brief period of departure frominflation sandwiched between two stages of slow roll inflation. We show that such a background behavior leads to a step like featurein the scalar power spectrum.We set the scales such that the drop in the power spectrum occurs at a length scale that corresponds to the Hubble radius today — a feature that seems necessary to explain the lower power observed in the quadrupole moment of the Cosmic Microwave Background (CMB) anisotropies. We perform a Markov Chain Monte Carlo analysis to determine the values of the model parameters that provide the best fit to the recent WMAP 5-year data for the CMB angular power spectrum. We find that an inflationary spectrum with a suppression of power at large scales that we obtain leads to a much better fit (with justone extra parameter, χeff2 improves by 6.62) of the observed data when compared to the best fit reference ΛCDM model with a featureless, power law, primordial spectrum.

Inflationary spectra from Lorentz violating dissipative models

The sensitivity of inflationary spectra to initial conditions is addressed in the context of a phenomenological model that breaks Lorentz invariance by dissipative effects above some threshold energy {lambda}. These effects are obtained dynamically by coupling the fluctuation modes to extra degrees of freedom which are unobservable below {lambda}. Because of the strong dissipative effects in the early propagation, only the state of the extra degrees of freedom is relevant for the power spectrum. If this state is the ground state, and if {lambda} is much larger than the Hubble scale H, the standard spectrum is recovered. Using analytical and numerical methods, we calculate the modifications for a large class of dissipative models. For all of these, we show that the leading modification (in an expansion in H/{lambda}) is linear in the decay rate evaluated at horizon exit, and that high frequency superimposed oscillations are not generated. The modification is negative when the decay rate decreases slower than the cube of H, which means that there is a loss of power on the largest scales.

Damped corrections to inflationary spectra from a fluctuating cutoff

We reconsider trans-Planckian corrections to inflationary spectra by taking into account a physical effect which has been overlooked and which could have important consequences. We assume that the short length scale characterizing the new physics is endowed with a finite width, the origin of which could be found in quantum gravity. As a result, the leading corrections responsible for superimposed oscillations in the cosmic microwave background temperature anisotropies are generically damped by the blurring of the UV scale. To determine the observational ramifications of this damping, we compare it to that which effectively occurs when computing the angular power spectrum of temperature anisotropies. The former gives an overall change of the oscillation amplitudes whereas the latter depends on the angular scale. Therefore, in principle they could be distinguished. In any case, the observation of superimposed oscillations would place a tight constraint on the variance of the UV cutoff.

Constraints on the inflationary expansion from three-year WMAP, small scale CMBanisotropies and large scale structure data sets

We present the constraints on inflationary parameters in a flatΛCDM universe obtained from the Wilkinson Microwave Anisotropy Probe (WMAP)three-year data release, plus smaller scale cosmic microwave background (CMB)and two large scale structure (LSS) data sets, 2dF and the Sloan Digital SkySurvey (SDSS) (treated separately). We use a Markov chain Monte Carlo (MCMC)technique combined with an analytic description of the inflationary spectra in termsof the horizon flow functions (HFF). By imposing a consistency condition forthe tensor-to-scalar ratio, we study the constraints on both single field standardinflation and on inflation with the violation of the null energy condition, whichleads to a blue spectrum for gravitational waves. For standard inflation, theconstraint on the tensor-to-scalar ratio we obtain from CMB data and 2dF05 isr0.01<0.26 at2σ confidence level. Without the consistency condition between the tensor-to-scalar ratio and thetensor slope, the constraint on the tensor amplitude is not significantly changed, but theconstraints on the HFFs are significantly relaxed. We then show that when the third HFFϵ3 is allowed to be non-zero and to be of order unity, a large negative (at2σ) value for the running of the scalar spectral index in standard inflation is found in any setof data we consider.

Planck scale inflationary spectra from quantum gravity

We derive the semiclassical evolution of massless minimally coupled scalar matter in the de Sitter space-time from the Born-Oppenheimer reduction of the Wheeler-DeWitt equation. We show that the dynamics of trans-Planckian modes can be cast in the form of an effective modified dispersion relation and that high energy corrections in the power spectrum of the cosmic microwave background radiation produced during inflation remain very small if the initial state is the Bunch-Davies vacuum.