Thermal Inflation Scenario Research Articles

Small-scale effects of thermal inflation on halo abundance at high- z , galaxy substructure abundance, and 21-cm power spectrum

We study the impact of thermal inflation on the formation of cosmological structures and present astrophysical observables which can be used to constrain and possibly probe the thermal inflation scenario. These are dark matter halo abundance at high redshifts, satellite galaxy abundance in the Milky Way, and fluctuation in the 21-cm radiation background before the epoch of reionization. The thermal inflation scenario leaves a characteristic signature on the matter power spectrum by boosting the amplitude at a specific wave number determined by the number of e-foldings during thermal inflation (${N}_{bc}$), and strongly suppressing the amplitude for modes at smaller scales. For a reasonable range of parameter space, one of the consequences is the suppression of minihalo formation at high redshifts and that of satellite galaxies in the Milky Way. While this effect is substantial, it is degenerate with other cosmological or astrophysical effects. The power spectrum of the 21-cm background probes this impact more directly, and its observation may be the best way to constrain the thermal inflation scenario due to the characteristic signature in the power spectrum. The Square Kilometre Array (SKA) in phase 1 (SKA1) has sensitivity large enough to achieve this goal for models with ${N}_{bc}\ensuremath{\gtrsim}26$ if a 10000-hr observation is performed. The final phase SKA, with anticipated sensitivity about an order of magnitude higher, seems more promising and will cover a wider parameter space.

CMB spectral distortion constraints on thermal inflation

Thermal inflation is a second epoch of exponential expansion at typical energy scales V1/4 ∼ 106 ∼ 8 GeV. If the usual primordial inflation is followed by thermal inflation, the primordial power spectrum is only modestly redshifted on large scales, but strongly suppressed on scales smaller than the horizon size at the beginning of thermal inflation, k > kb = ab Hb. We calculate the spectral distortion of the cosmic microwave background generated by the dissipation of acoustic waves in this context. For kb ≪ 103 Mpc−1, thermal inflation results in a large suppression of the μ-distortion amplitude, predicting that it falls well below the standard value of μ ≃ 2× 10−8. Thus, future spectral distortion experiments, similar to PIXIE, can place new limits on the thermal inflation scenario, constraining kb ≳ 103 Mpc−1 if μ ≃ 2× 10−8 were found.

Thermal inflation with flaton chemical potential

Thermal inflation driven by a scalar field called "flaton" is a possible scenario to solve the cosmological moduli problem. We study a model of thermal inflation with a flaton chemical potential. In the presence of the chemical potential, a negative mass squared of the flaton, which is necessary to terminate the thermal inflation, is naturally induced. We identify the allowed parameter region for the chemical potential ($\mu$) and the flaton self-coupling constant to solve the cosmological moduli problem and satisfy theoretical consistencies. In general, the chemical potential is a free parameter and it can be taken to be much larger than the typical scale of soft supersymmetry breaking parameters of $\mathcal{O} (1)$ TeV. For $\mu \gtrsim 10^8$ GeV, we find that the reheating temperature after the thermal inflation can be high enough for the thermal leptogenesis scenario to be operative. This is in sharp contrast to the standard thermal inflation scenario, in which the reheating temperature is quite low and a special mechanism is necessary for generating sufficient amount of baryon asymmetry in the Universe after thermal inflation.

Curvaton as dark matter with secondary inflation

We consider a novel cosmological scenario in which a curvaton is long-lived and plays the role of cold dark matter (CDM) in the presence of a short, secondary inflation. Non-trivial evolution of the large scale cosmological perturbation in the curvaton scenario can affect the duration of the short term inflation, resulting in the inhomogeneous end of inflation. Non-linear parameters of the curvature perturbation are predicted to be fNL ≈ 5/4 and gNL ≈ 0. The curvaton abundance can be well diluted by the short-term inflation and accordingly, it does not have to decay into the Standard Model particles. Then the curvaton can account for the present CDM with the isocurvature perturbation being sufficiently suppressed because both the adiabatic and CDM isocurvature perturbations have the same origin. As an explicit example, we consider the thermal inflation scenario and a string axion as a candidate for this curvaton-dark matter. We further discuss possibilities to identify the curvaton-dark matter with the QCD axion.

Effects of thermal fluctuations on thermal inflation

The mechanism of thermal inflation, a relatively short period of accelerated expansion after primordial inflation, is a desirable ingredient for a certain class of particle physics models if they are not to be in contention with the cosmology of the early Universe. Though thermal inflation is most simply described in terms of a thermal effective potential, a thermal environment also gives rise to thermal fluctuations that must be taken into account. We numerically study the effects of these thermal fluctuations using lattice simulations. We conclude that though they do not ruin the thermal inflation scenario, the phase transition at the end of thermal inflation proceeds through phase mixing and is therefore not accompanied by the formations of bubbles nor appreciable amplitude of gravitational waves.

Cosmological moduli problem in large volume scenario and thermal inflation

We show that in a large volume scenario of type IIB string or F-theory compactifications, single thermal inflation provides only a partial solution to the cosmological problem of the light volume modulus. We then clarify the conditions for double thermal inflation, being a simple extension of the usual single thermal inflation scenario, to solve the cosmological moduli problem in the case of relatively light moduli masses. Using a specific example, we demonstrate that double thermal inflation can be realized in large volume scenario in a natural manner, and the problem of the light volume modulus can be solved for the whole relevant mass range. We also find that right amount of baryon asymmetry and dark matter can be obtained via a late-time Affleck-Dine mechanism and the decays of the visible sector NLSP to flatino LSP.

Theμproblem and the axion in gauge mediation

We revisit the idea of generating the Higgs mu parameter through a spontaneously broken Peccei-Quinn (PQ) symmetry in gauge-mediated supersymmetry breaking scenario. For the messenger scale of gauge mediation higher than the PQ scale, the setup naturally generates mu ~ m_soft and the Higgs soft parameter B \leq O(m_soft) with the CP phase of B aligned to the phase of gaugino masses, while giving the PQ scale v_PQ ~ \surd (m_soft {\Lambda}), where m_soft denote the gauge-mediated gaugino or sfermion masses and {\Lambda} is the cutoff scale which can be identified as the Planck scale or the GUT scale. The PQ sector of the model results in distinctive cosmology including a late thermal inflation. We discuss the issue of dark matter and baryogenesis in the resulting thermal inflation scenario, and find that a right amount of gravitino dark matter can be produced together with a successful Affleck-Dine leptogenesis, when the gravitino mass m_{3/2} = O(100) keV.

Density fluctuations in thermal inflation and non-Gaussianity

We consider primordial fluctuations in thermal inflation scenario. Since the thermal inflation drives about 10 e-folds after the standard inflation, the time of horizon-exit during inflation corresponding to the present observational scale shifts toward the end of inflation. It generally makes the primordial power spectrum more deviated from a scale-invariant one and hence renders some models inconsistent with observations. We present a mechanism of generating the primordial curvature perturbation at the end of thermal inflation utilizing a fluctuating coupling of a flaton field with the fields in thermal bath. We show that, by adopting the mechanism, some inflation models can be liberated even in the presence of the thermal inflation. We also discuss non-Gaussianity in the mechanism and show that large non-Gaussianity can be generated in this scenario.

Cosmological implications of radiatively generated axion scale

We study cosmological implications of supersymmetric axion models in which the axion scale is generated radiatively. Such models lead to the so-called thermal inflation and subsequent reheating should be constrained not to yield to a too large axion energy density at the time of nucleosynthesis. We examine how plausible it is that this nucleosynthesis constraint is satisfied for both hadronic and Dine-Fischler-Srednicki-Zhitnitskii type axion models. Baryogenesis and the possibility for raising up the cosmological upper bound on the axion scale in thermal inflation scenario are also discussed.