Warm Inflation Scenario Research Articles

Testing models of inflation with cosmic microwave background non-Gaussianity

Two different predictions for the primordial curvature fluctuation bispectrum arecompared through their effects on the cosmic microwave background temperaturefluctuations. The first has a local form described with a single parameterfNL. The second is based on a prediction from the warm inflationaryscenario, with a different dependence on wavenumber and a parameterfWI. New expressions are obtained for the angular bispectra of thetemperature fluctuations and for the estimators used to determinefNL and fWI. The standard deviation of the estimators in an ideal experiment is roughly5 timeslarger for fWI than for fNL. Using three-year WMAP (Wilkinson Microwave Anisotropy Probe) data gives limits−375<fWI<36.8, but there is a possibility of detecting a signal forfWI from the Planck satellite.

Warm inflation dynamics in the low temperature regime

Warm inflation scenarios are studied with the dissipative coefficient computed in the equilibrium approximation. Use is made of the analytical expressions available in the low temperature regime with focus on the possibility of achieving strong dissipation within this approximation. Two different types of models are examined: monomial or equivalently chaotic type potentials, and hybrid like models where the energy density during inflation is dominated by the false vacuum. In both cases dissipation is shown to typically increase during inflation and bring the system into the strong dissipative regime. Observational consequences are explored for the amplitude of the primordial spectrum and the spectral index, which translate into constraints on the number of fields mediating the dissipative mechanism, and the number of light degrees of freedom produced during inflation. This paper furthers the foundational development of warm inflation dynamics from first principles quantum field theory by calculating conservative lower bound estimates on dissipative effects during inflation using the well established thermal equilibrium approximation. This approximation does not completely represent the actual physical system and earlier work has shown relaxing both the equilibrium and low temperature constraints can substantially enlarge the warm inflation regime, but these improvements still need further theoretical development.

Cosmological perturbations in warm inflationary models with viscous pressure

Scalar and tensorial cosmological perturbations generated in warm inflationary scenarios whose matter-radiation fluid is endowed with a viscous pressure are considered. Recent observational data from the Wilkinson Microwave Anisotropy Probe experiment are employed to restrict the parameters of the model. Although the effect of this pressure on the matter power spectrum is of the order of a few percent, it may be detected in future experiments.

Non-Gaussianity in fluctuations from warm inflation

The scalar mode density perturbations in the warm inflationary scenario are analysed witha view to predicting the amount of non-Gaussianity produced by this scenario. The analysisassumes that the inflaton evolution is strongly damped by the radiation, with dampingterms that are temperature independent. Entropy fluctuations during warm inflation play acrucial role in generating non-Gaussianity and result in a distinctive signal which should beobservable by the Planck satellite.

Dynamics and non-Gaussianity in the weak-dissipative warm inflation scenario

We calculate the general solutions for a warm inflationary scenario with weak dissipation, reviewing the dissipative dynamics of the two-fluid system, and calculate the bispectrum of the gravitational field fluctuations generated in the case where dissipation of the vacuum potential during inflation is the mechanism for structure formation, but is the subdominant effect in the dynamics of the scalar field during slow-roll. The bispectrum is nonzero because of the self-interaction of the scalar field. We compare the predictions with both those of standard, or ``supercooled``, inflationary models, and warm inflation models with strong dissipation and consider the detectability of these levels of non-Gaussianity in the bispectrum of the cosmic microwave background. We find that the levels of non-Gaussianity for warm and supercooled inflation are an order of magnitude different.

Asymptotic behavior of the warm inflation scenario with viscous pressure

We analyze the dynamics of models of warm inflation with general dissipative effects. We consider phenomenological terms both for the inflaton decay rate and for viscous effects within matter. We provide a classification of the asymptotic behavior of these models and show that the existence of a late-time scaling regime depends not only on an asymptotic behavior of the scalar field potential, but also on an appropriate asymptotic behavior of the inflaton decay rate. There are scaling solutions whenever the latter evolves to become proportional to the Hubble rate of expansion regardless of the steepness of the scalar field exponential potential. We show from thermodynamic arguments that the scaling regime is associated with a power-law dependence of the matter-radiation temperature on the scale factor, which allows a mild variation of the temperature of the matter/radiation fluid. We also show that the late-time contribution of the dissipative terms alleviates the depletion of matter, and increases the duration of inflation.

Sneutrino warm inflation in the minimal supersymmetric model

The model of RH neutrino fields coupled to the MSSM is shown to yield a large parameter regime of warm inflation. In the strong dissipative regime, it is shown that inflation, driven by a single sneutrino field, occurs with {\it all field amplitudes below the Planck scale}. Analysis is also made of leptogenesis, neutrino mass generation and gravitino constraints. A new warm inflation scenario is purposed in which one scalar field drives a period of warm inflation and a second field drives a subsequent phase of reheating. Such a model is able to reduce the final temperature after inflation, thus helping to mitigate gravitino constraints.

Spontaneous baryogenesis in warm inflation

We discuss spontaneous baryogenesis in the warm inflation scenario. In contrast with standard inflation models, radiation always exists in the warm inflation scenario, and the inflaton must be directly coupled to it. Also, the transition to the post-inflationary radiation dominated phase is smooth and the entropy is not significantly increased at the end of the period of inflation. In addition, after the period of warm inflation ends, the inflaton does not oscillate coherently but slowly rolls. We show that as a consequence of these features of warm inflation, the scenario can well accommodate the spontaneous baryogenesis mechanism, provided that the decoupling temperature $T_{D}$ of the baryon or the $B-L$ violating interactions is higher than the temperature of radiation during the late stages of inflation.

Synergistic warm inflation

We consider an alternative warm inflationary scenario in which n scalar fields coupled to a dissipative matter fluid cooperate to produce power-law inflation. The scalar fields are driven by an exponential potential and the bulk dissipative pressure coefficient is linear in the expansion rate. We find that the entropy of the fluid attains its asymptotic value in a characteristic time proportional to the square of the number of fields. This scenario remains nearly isothermal along the inflationary stage. The perturbations in energy density and entropy are studied in the long-wavelength regime and seen to grow roughly as the square of the scale factor. They are shown to be compatible with COBE measurements of the fluctuations in temperature of the CMB.

Gravitino production in the warm inflationary scenario

We estimate the production of gravitinos during and after the end of a period of warm inflation, a model in which radiation is produced continuously as the field rolls down the potential producing dissipation. We find that gravitino production is efficient for models in the strong dissipation regime, with the result that standard nucleosynthesis is disrupted unless the magnitude of the inflaton potential is very small. Combining this with the constraint from the thermal production of adiabatic density perturbations, we find the dissipation rate must be extraordinarily strong, or that the potential is very flat.

Warm Inflation and Scalar Perturbations of the Metric

A second-order expansion for the quantum fluctuations of the matter field was considered in the framework of the warm inflation scenario. The friction and Hubble parameters were expended by means of a semiclassical approach. The fluctuations of the Hubble parameter generates fluctuations of the metric. These metric fluctuations produce an effective term of curvature. The power spectrum for the metric fluctuations can be calculated on the infrared sector.

A relativistic calculation of super-Hubble suppression ofinflation with thermal dissipation

We investigated the evolution of the primordial density perturbationsproduced by inflation with thermal dissipation. A full relativistic analysison the evolution of initial perturbations from the warm inflation era to aradiation-dominated universe has been developed. The emphasis is ontrackingthe ratio between the adiabatic and the isocurvature mode of the initialperturbations. This result is employed to calculate a testable factor: thesuper-Hubble suppression of the power spectrum of the primordialperturbations. We show that based on the warm inflation scenario, thesuper-Hubble suppression factor, s, for an inflation with thermaldissipation is at least 0.5. This prediction does not depend on thedetailsof the model parameters. If s is larger than 0.5, it implies that thefriction parameter Γ is larger than the Hubble expansionparameter Hduring the inflation era.

Perturbation spectra in the warm inflationary scenario

We investigate the phenomenology of warm inflation and present generic results about the evolution of the inflaton and radiation fields. The general conditions required for warm inflation to take place are derived and discussed. A comprehensive approach is presented for the generation of thermally induced adiabatic and isocurvature perturbations and the amplitude of their spectra calculated. In addition we derive the ratio of tensor-to-scalar perturbations and find the spectral indices for adiabatic, isocurvature and tensor perturbations formed in the warm inflationary era. These results are presented in a simplified and compact approach that is generally applicable. Our results are illustrated by inflation models with polynomial and exponential potentials. We compare our analytic results against numerical models and find excellent agreement. Finally, presently available data is used to put constraints on warm inflation and we discuss how near--future observations may distinguish the warm inflationary scenario from standard supercooled inflation. The main observable difference is the different scalar-to- tensor ratio, and that the consistency relation between this and the slope of tensor perturbations does not hold for warm inflation.

Primordial fluctuations in the warm inflation scenario with a more realistic coarse-grained field

I study a semiclassical approach to the warm inflation scenario introduced in previous works. In this work, I define the fluctuations for the matter field by means of a new coarse-grained field with a suppression factor G. This field describes the matter fluctuations on the now observable scale of the universe. The power spectrum for the fluctuations of the matter field is analyzed in both de Sitter and power-law expansions for the universe. The constraint for the spectral index gives a constraint for the mass of the matter field in the de Sitter expansion and a constraint for the friction parameter in the power-law expansion for the universe.

Erratum: Power spectrum of the primordial scalar field fluctuations in the warm inflation scenario [Phys. Rev. D 58, 103518 (1998)

Erratum: Power spectrum of the primordial scalar field fluctuations in the warm inflation scenario [Phys. Rev. D 58, 103518 (1998)

Towards a theory of warm inflation of the Universe

The warm inflation scenario is an alternative mechanism which can explain the isotropic and homogeneous Universe in which we are living. In this work I extend a previously introduced formalism, without the restriction of the slow-roll regime. Quantum to classical transition of the fluctuations is studied by means of the `transition function' here introduced. I found that the fluctuations of radiation energy density decrease with time and the thermal equilibrium at the end of inflation holds.

Power spectrum of the primordial scalar field fluctuations in the warm inflation scenario

A new model of warm inflation without slow-roll conditions for the scalar field is studied. Classicality conditions that must be satisfied to have an effective stochastic approach in the warm inflation scenario are analyzed for a general coarse-grained field, defined with a function that describes the long wavelength suppression. The theory can predict the spectral density of the fluctuations of the field which can be compared with the COBE data. @S0556-2821~98!11020-2# PACS number~s!: 98.80.Cq, 05.40.1j, 98.70.Vc In 1995 Berera and Fang @1# showed how thermal fluctuations during inflation may play the dominant role in producing the initial perturbations, invoking the slow-roll approximation through a combination of a flat potential and dissipative damping. This idea was extended in @2,3# into the warm inflation scenario. This scenario differs from supercooled inflation scenarios in that reheating is no longer necessary and de Sitter expansion and radiation energy production occur together. The Universe we will consider is still dominated by the vacuum energy of the field, with the thermal component being small. The motivation of this work is the study of the quantum to classical transition in the warm inflation scenario and the spectral density of the fluctuations of an arbitrary coarsegrained scalar field. In this work I consider a general case, where the dynamics of a scalar field is minimally coupled to a classical gravitational one. The system is described by the Lagrangian

Warm inflation and classicality conditions

In this work we analize the classicality conditions that must be satisfied to have an effective stochastic approach, in the framework of warm inflation scenarios. The radiation temperature at the end of inflation is of the order of 10 14 GeV, for an scalar field with mass m ∼(10 −4 – 10 −5 ) M p , and the energy fluctuations decreases with the time.