Scalar Power Spectrum Research Articles

DBI inflation and warped black holes

We study a possible amplification mechanism for the curvature perturbations generated during inflation by a Dirac-Born-Infeld (DBI) inflaton in the presence of a sharp feature in the warp factor. The large growth resulting in the scalar power spectrum is a consequence of the decreasing speed of sound. We obtain analytical approximate expressions for the relevant dynamical quantities both in the slow roll phase and during the transient phase which leads to the amplification. We finally compare our approximations to the exact numerical evolution and give, in such a context, the general rules for building a viable inflationary model leading to, during the subsequent radiation dominated era, an abundant primordial black holes formation.

Импульсивность — рефлексивность и нейроэффективность интеллектуальной деятельности

A brief review of current research into the problem of cognitive neuroefficiency revealed a large array of conflicting data. Some studies provide evidence of lower energy consumption and faster cognitive activity in respondents with high IQ, while others show higher energy consumption and slower speed. Other datasets indicate that respondents with high intelligence are more reflexive than those with low intelligence. The heterogeneity of the samples is indicated as a key reason for the inconsistency of the data. This study aimed to compare behavioral and electroencephalographic data in groups of respondents homogeneous in terms of (a) sex, (b) age, and (c) manifestations of the cognitive style Impulsivity-Reflexivity. The study sample consisted of three age groups: 92 people aged 13.73 ± 0.45 years (44.5% of men), 123 people aged 15.46 ± 0.66 years (52% of men), 36 people aged 21.11±2.87 years (44.4% of men). The diagnostic procedure included the collection of behavioral data (Cognitive Personality Style Questionnaire CPS-Q, Raven’s SPM, Amtrhauer’s Intelligence Structure Test, Rusalov’s Personality Formal Dynamic Properties Questionnaire) and data on the bioelectrical activity of the cerebral cortex at rest and during the detection of similar figures J. Kagan. Comparative data analysis (U-test; H-test) showed that women demonstrate significantly higher intelligence indicators, detect similar figures with greater accuracy, but at the same time expend more energy in terms of the EEG power spectrum, compared with men. Significant differences in intelligence and Impulsivity-Reflexivity among age groups were not found. However, a significant decrease in the EEG power spectrum was revealed under electrodes O1, C3, Oz, Pz, CP4 while solving Kagan’s tasks from the younger to the older age group. A paradoxical result was obtained when comparing groups of respondents significantly different in terms of the Impulsivity-Reflexivity of the Kagan test. Significant differences in the EEG power spectrum, CPS-Q Impulsivity and Reflexivity scales, and intelligence were not found. A hypothesis was put forward about the false discriminant validity of the Kagan test for respondents with low IQ.

Gravitational wave trispectrum in the axion-SU(2) model

We study the trispectrum of the gravitational waves (GWs) generated through the dynamics of an axionic spectator field and SU(2) gauge fields during inflation. In non-Abelian gauge theory, the gauge fields have four-point self-interactions, which induce the tree-level GW trispectrum. We formulate this type of the GW trispectrum including the non-dynamical contributions and evaluate it in the equilateral limit as a unique signal of this model. We find that the ratio of the GW trispectrum to the cube of the scalar power spectrum can be as large as \U0001d4aa(106) in the viable parameter space, which could be captured in the CMB observations.

Exploring the parameter space of modified supergravity for double inflation and primordial black hole formation

We study the parameter space of the effective (with two scalars) models of cosmological inflation and primordial black hole (PBH) formation in the modified (R + R 2) supergravity. Our models describe double inflation, whose first stage is driven by Starobinsky’s scalaron coming from the R 2 gravity, and whose second stage is driven by another scalar belonging to the supergravity multiplet. The ultra-slow-roll regime between the two stages leads a large peak (enhancement) in the power spectrum of scalar perturbations, which results in efficient PBH formation. Both inflation and PBH formation are generic in our models, while those PBH can account for a significant part or the whole of dark matter. Some of the earlier proposed models in the same class are in tension (over 3σ) with the observed value of the scalar tilt n s, so that we study more general models with more parameters, and investigate the dependence of the cosmological tilts (n s, r) and the scalar power spectrum enhancement upon the parameters. The PBH masses and their density fraction (as part of dark matter) are also calculated. A good agreement (between 2σ and 3σ) with the observed value of n s requires fine tuning of the parameters, and it is only realized in the so-called δ-models. Our models offer the (super)gravitational origin of inflation, PBH and dark matter together, and may be confirmed or falsified by future precision measurements of the cosmic microwave background radiation and PBH-induced gravitational waves.

Inflation story: slow-roll and beyond

We present constraints on inflationary dynamics and features in the primordial power spectrum of scalar perturbations using the Cosmic Microwave Background temperature, polarization data from Planck 2018 data release and updated likelihoods. We constrain the slow-roll dynamics using Hilltop Quartic Potential and Starobinsky R + R 2 model in the Einstein frame using the Planck 2018 binned Plik likelihood. Using the Hilltop as base potential, we construct Whipped Inflation potential to introduce suppression in the scalar power spectrum at large angular scales. We notice marginal (68% C.L.) preference of suppression from the large scale temperature angular power spectrum. However, large-scale E-mode likelihood based on high frequency instrument cross spectrum, does not support this suppression and in the combined data the preference towards the suppression becomes negligible. Based on the Hilltop and Starobinsky model, we construct the Wiggly Whipped Inflation potentials to introduce oscillatory features along with the suppression. We use unbinned data from the recently released CamSpec v12.5 likelihood which updates Planck 2018 results. We compare the Bayesian evidences of the feature models with their baseline slow-roll potentials. We find that the complete slow-roll baseline potential is moderately preferred against potentials which generate features. Compared to Planck 2015 PlikHM bin1 likelihood, we find that the significance of sharp features has decreased owing to the updates in the data analysis pipeline. We also compute the bispectra for the best fit candidates obtained from our analysis.

Primordial Black Holes And Gravitational Waves Based On No-Scale Supergravity

In this paper we present a class of models in order to explain the production of Primordial Black Holes (PBHs) and Gravitational Waves (GWs) in the Universe. These models are based on no-scale theory. By breaking the SU(2,1)/SU(2)×U(1) symmetry we fix one of the two chiral fields and we derive effective scalar potentials which are capable of generating PBHs and GWs. As it is known in the literature there is an important unification of the no-scale models, which leads to the Starobinsky effective scalar potential based on the coset SU(2,1)/SU(2)×U(1). We use this unification in order to additionally explain the generation of PBHs and GWs. Concretely, we modify well-known superpotentials, which reduce to Starobinsky-like effective scalar potentials. Thus, we derive scalar potentials which, on the one hand, explain the production of PBHs and GWs and, on the other hand, they conserve the transformation laws, which yield from the parametrization of the coset SU(2,1)/SU(2)×U(1) as well as the unification between the models which are yielded this coset. We numerically evaluate the scalar power spectra with the effective scalar potential based on this theory. Furthermore, we evaluate the fractional abundances of PBHs by comparing two methods the Press–Schechter approach and the peak theory, while focusing on explaining the dark matter in the Universe. By using the resulting scalar power spectrum we evaluate the amount of GWs. All models are in complete consistence with Planck constraints.

Improved DHOST Genesis

We improve the DHOST Genesis proposed in [1], such that the near scale invariant scalar power spectrum can be generated from the model itself, without invoking extra mechanism like a string gas. Besides, the superluminality problem of scalar perturbation plagued in [1] can be rescued by choosing proper DHOST action.

Scalar and tensor perturbations in DHOST bounce cosmology

We investigate the bounce realization in the framework of DHOST cosmology, focusing on the relation with observables. We perform a detailed analysis of the scalar and tensor perturbations during the Ekpyrotic contraction phase, the bounce phase, and the fast-roll expansion phase, calculating the power spectra, the spectral indices and the tensor-to-scalar ratio. Furthermore, we study the initial conditions, incorporating perturbations generated by Ekpyrotic vacuum fluctuations, by matter vacuum fluctuations, and by thermal fluctuations. The scale invariance of the scalar power spectrum can be acquired introducing a matter contraction phase before the Ekpyrotic phase, or invoking a thermal gas as the source. The DHOST bounce scenario with cosmological perturbations generated by thermal fluctuations proves to be the most efficient one, and the corresponding predictions are in perfect agreement with observational bounds. Especially the tensor-to-scalar ratio is many orders of magnitude within the allowed region, since it is suppressed by the Hubble parameter at the beginning of the bounce phase.

Geometry versus growth

We carry out a multi-probe self-consistency test of the flat Lambda Cold Dark Matter (ΛCDM) model with the aim of exploring potential causes of the reported tensions between high- and low-redshift cosmological observations. We divide the model into two theory regimes determined by the smooth background (geometry) and the evolution of matter density fluctuations (growth), each governed by an independent set of ΛCDM cosmological parameters. This extended model is constrained by a combination of weak gravitational lensing measurements from the Kilo-Degree Survey, galaxy clustering signatures extracted from Sloan Digital Sky Survey campaigns and the Six-Degree Field Galaxy Survey, and the angular baryon acoustic scale and the primordial scalar fluctuation power spectrum measured in Planck cosmic microwave background (CMB) data. For both the weak lensing data set individually and the combined probes, we find strong consistency between the geometry and growth parameters, as well as with the posterior of standard ΛCDM analysis. In the non-split analysis, for which one single set of parameters was used, tension in the amplitude of matter density fluctuations as measured by the parameter S8 persists at around 3σ, with a 1.5% constraint of S8 = 0.776−0.008+0.016 for the combined probes. We also observe a less significant preference (at least 2σ) for higher values of the Hubble constant, H0 = 70.5−1.5+0.7 km s−1 Mpc−1, as well as for lower values of the total matter density parameter Ωm = 0.289−0.005+0.007 compared to the full Planck analysis. Including the subset of the CMB information in the probe combination enhances these differences rather than alleviate them, which we link to the discrepancy between low and high multipoles in Planck data. Our geometry versus growth analysis does not yet yield clear signs regarding whether the origin of the discrepancies lies in ΛCDM structure growth or expansion history but holds promise as an insightful test for forthcoming, more powerful data.

Primordial black holes formation in the inflationary model with field-dependent kinetic term for quartic and natural potentials

Within the framework of inflationary model with field-dependent kinetic term for quartic and natural potentials, we investigate generation of the primordial black holes (PBHs) and induced gravitational waves (GWs). In this setup, we consider a kinetic function as G(phi )=g_I(phi )big (1+g_{II}(phi )big ) and show that in the presence of first term g_I(phi ) both quartic and natural potentials, in contrast to the standard model of inflation, can be consistent, with the 68% CL of Planck observations. Besides, the second term g_{II}(phi ) can cause a significant enhancement in the primordial curvature perturbations at the small scales which results the PBHs formation. For the both potentials, we obtain an enhancement in the scalar power spectrum at the scales ksim 10^{12}~{mathrm{Mpc}}^{-1}, 10^{8}~{mathrm{Mpc}}^{-1}, and 10^{5}~{mathrm{Mpc}}^{-1}, which causes PBHs production in mass scales around 10^{-13}M_{odot }, 10^{-5}M_{odot }, and 10 M_{odot }, respectively. Observational constraints confirm that PBHs with a mass scale of 10^{-13}M_{odot } can constitute the total of dark matter in the universe. Furthermore, we estimate the energy density parameter of induced GWs which can be examined by the observation. Also we conclude that it can be parametrized as a power-law function Omega _{mathrm{GW}}sim (f/f_c)^n, where the power index equals n=3-2/ln (f_c/f) in the infrared limit fll f_{c}.

Unifying an asymmetric bounce to the dark energy in Chern–Simons F(R) gravity

We propose a cosmological scenario in which the universe undergoes through a non-singular bounce, and after the bounce, it decelerates having a matter-like dominated evolution during some regime of the deceleration era, and finally at the present epoch it evolves through an accelerating stage. Our aim is to study such evolution in the context of Chern–Simons corrected F(R) gravity theory and confront the model with various observational data. Using the reconstruction technique, and in addition by employing suitable boundary conditions, we determine the form of F(R) for the entire possible range of the cosmic time. The form of F(R) seems to unify a non-singular bounce with a dark energy epoch, in particular, from a non-singular bounce to a deceleration epoch and from a deceleration epoch to a late time acceleration era. It is important to mention that the bouncing scenario in the present context is an asymmetric bounce, in particular, the Hubble radius monotonically increases and asymptotically diverges at the late contracting era, while it seems to decrease with time at the present epoch. The decreasing behaviour of the Hubble radius ensures a late time acceleration era of the universe. Moreover, due to the aforesaid evolution of the Hubble radius, the primordial perturbation modes generate at the deep contracting era far away from the bounce when all the perturbation modes lie within the horizon. Correspondingly we calculate the scalar and tensor power spectra, and accordingly, we evaluate the primordial observable quantities like the spectral index of the scalar curvature perturbation, the tensor-to-scalar ratio, and as a result, they are found to be in agreement with the latest Planck 2018 constraints. In this regard, the Chern–Simons term seems to have considerable effects on the tensor perturbation evolution, however keeping intact the scalar part of the perturbation with that of in the case of a vacuum F(R) model, and as a result, the Chern–Simons term proves to play an important role in making the observable quantities consistent with the Planck results. Furthermore the theoretical expectation of the effective equation of state parameter of the dark energy epoch is confronted with the Planck+SNe+BAO data.

Resonant features in the stochastic gravitational wave background

We analyse the post-inflationary contribution to the stochastic gravitational wave background due to a resonant feature in the scalar power spectrum, which is characterised by an oscillation in log(k), complementing our previous work arXiv:2012.02761 on sharp features. Primordial features signal departures of inflation from the single-field slow-roll paradigm and are motivated by embeddings of inflation in high energy physics. We find that the oscillation in the scalar power spectrum leads to a corresponding modulation in the gravitational wave spectrum that can be understood as a superposition of two oscillatory pieces, one with the original frequency of the scalar oscillations, and one with double frequency. For oscillations with slowly-varying amplitude this oscillatory part can be computed semi-analytically. Our results can be used as templates for the reconstruction of the signal from future data and permit extracting information about the small scale scalar power spectrum from measurements of the stochastic gravitational wave background.

Oscillations in the stochastic gravitational wave background from sharp features and particle production during inflation

We identify a characteristic pattern in the scalar-induced stochastic gravitational wave background from particle production during inflation.If particle production is sufficiently efficient, the scalar power spectrum exhibits \U0001d4aa(1) oscillations periodic in k, characteristic of a sharp feature, with an exponentially enhanced envelope. We systematically study the properties of the induced spectrum of gravitational waves sourced after inflation and find that this inherits the periodic structure in k, resulting in a peak in the gravitational wave energy density spectrum with \U0001d4aa(10 %) modulations. The frequency of the oscillation in the scalar power spectrum is determined by the scale of the feature during inflation and in turn sets the frequency of modulations in the gravitational wave signal. We present an explicit realisation of this phenomenon in the framework of multifield inflation, in the form of a strong sharp turn in the inflationary trajectory. The resulting stochastic background is potentially detectable in future gravitational wave observatories, and considerations of backreaction and perturbativity can be used to constrain the parameter space from the theoretical side. Our work motivates more extensive research linking primordial features to observable properties of the stochastic background of gravitational waves, and dedicated development in data analysis for their detection.

Primordial black holes and induced gravitational waves in k-inflation

Recent observational constraints indicate that primordial black holes (PBHs) with the mass scale ∼ 10-12M⊙ can explain most of dark matter in the Universe. To produce this kind of PBHs, we need an enhance in the primordial scalar curvature perturbations to the order of \U0001d4aa(10-2) at the scale k ∼ 1012 Mpc-1. Here, we investigate the production of PBHs and induced gravitational waves (GWs) in the framework of k-inflation. We solve numerically the Mukhanov-Sasaki equation to obtain the primordial scalar power spectrum. In addition, we estimate the PBHs abundance fPBH peak as well as the energy density parameter ΩGW,0 of induced GWs. Interestingly enough is that for a special set of model parameters, we estimate the mass scale and the abundance of PBHs as ∼ O(10-13)M⊙ and fPBH peak=0.96, respectively. This confirms that the mechanism of PBHs production in our inflationary model can justify most of dark matter. Furthermore, we evaluate the GWs energy density parameter and conclude that it behaves like a power-law function ΩGW∼ (f/fc)n where in the infrared limit f≪ fc, the power index reads n=3-2/ln(fc/f).

Breaking the degeneracy between polarization efficiency and cosmological parameters in CMB experiments

Accurate cosmological parameter estimates using polarization data of the cosmic microwave background (CMB) put stringent requirements on map calibration, as highlighted in the recent results from the Planck satellite. In this paper, we point out that a model-dependent determination of polarization calibration can be achieved by the joint fit of the temperature-E-mode cross-power spectrum (TE) and E-mode auto-power spectrum (EE). This provides a valuable cross-check to band-averaged polarization efficiency measurements determined using other approaches. We demonstrate that, in $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$, the combination of the TE and EE constrain polarization calibration with sub-percent uncertainty with Planck data and 2% uncertainty with sptpol data. We arrive at similar conclusions when extending $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ to include the amplitude of lensing ${A}_{\mathrm{L}}$, the number of relativistic species ${N}_{\mathrm{eff}}$, or the sum of the neutrino masses $\ensuremath{\sum}{m}_{\ensuremath{\nu}}$. The uncertainties on cosmological parameters are minimally impacted when marginalizing over polarization calibration, except, as can be expected, for the uncertainty on the amplitude of the primordial scalar power spectrum $\mathrm{ln}({10}^{10}{A}_{\mathrm{s}})$, which increases by 20--50%. However, this information can be fully recovered by adding temperature auto-power spectrum (TT) information. For current and future ground-based experiments, SPT-3G and CMB-S4, we forecast the cosmological parameter uncertainties to be minimally degraded when marginalizing over polarization calibration parameters. In addition, CMB-S4 could constrain its polarization calibration at the level of $\ensuremath{\sim}0.2%$ by combining TE and EE, and reach $\ensuremath{\sim}0.06%$ by also including TT. We therefore conclude that relying on calibrating against Planck polarization maps, whose statistical uncertainty is limited to $\ensuremath{\sim}0.5%$, would be insufficient for upcoming experiments.

Measuring the scalar induced gravitational waves from observations

We consider the scalar induced gravitational waves from the cosmic microwave background (CMB) observations and the gravitational wave observations. In the Lambda CDM+r model, we constrain the cosmological parameters within the evolution of the scalar induced gravitational waves by the additional scalar power spectrum. The two special cases called narrow power spectrum and wide power spectrum have influence on the cosmological parameters, especially the combinations of Planck18+BAO+BK15+LISA. We also compare these numerical results from four datasets within LIGO, LISA, IPTA and FAST projects, respectively. The constraints from FAST have a significant impact on tensor-to-scalar ratio. Besides, we only consider the relic density of induced gravitational waves with respect to different frequencies from CMB scale to high frequencies including the range of LIGO and LISA.

Primordial black holes and secondary gravitational waves from chaotic inflation

Chaotic inflation is inconsistent with the observational constraint at 68% CL. Here, we show that the enhancement mechanism with a peak function in the noncanonical kinetic term not only helps the chaotic model V(ϕ) = V0ϕ1/3 satisfy the observational constraint at large scales but also enhances the primordial scalar power spectrum by seven orders of magnitude at small scales. The enhanced curvature perturbations can produce primordial black holes of different masses and secondary gravitational waves with different peak frequencies. We also show that the non-Gaussianities of curvature perturbations have little effect on the abundance of primordial black holes and energy density of the scalar-induced secondary gravitational waves.

Inflationary anisotropic phases with bianchi-I cosmic model

This paper is devoted to studying warm anisotropic inflation using modified Chaplygin gas in the context of the Bianchi-I comic model. We investigate the dynamics of the warm intermediate universe model in two distinct regimes, i.e., weak and strong regimes in the context of generalized dissipative coefficient. We formulate solutions of dissipation coefficient, inflaton field, scalar & tensor (S/T) power spectra, spectral index in an environment of slow-roll approximation to discuss the existence of warm weak and strong inflation and checked their viability in view of 2018 Planck data. It is seen through graphical representation that the condition for the existence of warm weak inflation is preserved only for z=0 and z=1 whereas in the case of the strong dissipative regime, the compatibility is achieved for z=3. The corresponding decay rates and the S/T are found to be consistent with the current observations.

Cosmic Tango Between the Very Small and the Very Large: Addressing CMB Anomalies Through Loop Quantum Cosmology

While the standard, six-parameter, spatially flat ΛCDM model has been highly successful, certain anomalies in the cosmic microwave background bring out a tension between this model and observations. The statistical significance of any one anomaly is small. However, taken together, the presence of two or more of them imply that according to standard inflationary theories we live in quite an exceptional Universe. We revisit the analysis of the PLANCK collaboration using loop quantum cosmology, where an unforeseen interplay between the ultraviolet and the infrared makes the primordial power spectrum scale dependent at very small k. Consequently, we are led to a somewhat different ΛCDM Universe in which anomalies associated with large scale power suppression and the lensing amplitude are both alleviated. The analysis also leads to new predictions for future observations. This article is addressed both to cosmology and loop quantum gravity communities, and we have attempted to make it self-contained.

Double peaks of gravitational wave spectrum induced from inflection point inflation

We investigate the possibility of inducing the gravitational waves (GWs) with double peak energy spectrum from primordial scalar perturbations in inflationary models with three inflection points. Here the inflection points can be generated from a polynomial potential or generated from a Higgs-like phi ^4 potential with the running of quartic coupling. In such models, the inflection point at large scales predicts the scalar spectral index and tensor-to-scalar ratio to be consistent with current CMB constraints, and the other two inflection points generate two large peaks in the scalar power spectrum at small scales, which can induce GWs with a double peak energy spectrum. We find that for some choices of the parameters the double peak spectrum can be detected by future GW detectors, and one of the peaks around fsimeq 10^{-9}{-}10^{-8} Hz can also explain the recent NANOGrav signal. Moreover, the peaks of the power spectrum allow for the generation of primordial black holes, which accounts for a significant fraction of dark matter.