Constraints on the radiation temperature before inflation [CL]

We consider the short period of cosmic expansion ranging from the end of the Planck era to the beginning of inflation and set upper and lower limits on the temperature of the radiation at the commencement of the inflationary phase.

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R. Herrera, D. Pavon and J. Saavedra
Fri, 19 Jan 18

Comments: 10 pages, 1 eps figure, key words: cosmology, early Universe, inflation, thermodynamics

Modulus D-term Inflation [CL]

We propose a new model of single-field D-term inflation in supergravity, where the inflation is driven by a single modulus field which transforms non-linearly under the U(1) gauge symmetry. One of the notable features of our modulus D-term inflation scenario is that the global U(1) remains unbroken in the vacuum and hence our model is not plagued by the cosmic string problem which can exclude most of the conventional D-term inflation models proposed so far due to the CMB observations.

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K. Kadota, T. Kobayashi, I. Saga, et. al.
Fri, 19 Jan 18

Comments: 15 pages, 5 figures

Initial conditions for Inflation in an FRW Universe [CL]

We examine the class of initial conditions which give rise to inflation. Our analysis is carried out for several popular models including: Higgs inflation, Starobinsky inflation, chaotic inflation, axion monodromy inflation and non-canonical inflation. In each case we determine the set of initial conditions which give rise to sufficient inflation, with at least $60$ e-foldings. A phase-space analysis has been performed for each of these models and the effect of the initial inflationary energy scale on inflation has been studied numerically. This paper discusses two scenarios of Higgs inflation: (i) the Higgs is coupled to the scalar curvature, (ii) the Higgs Lagrangian contains a non-canonical kinetic term. In both cases we find Higgs inflation to be very robust since it can arise for a large class of initial conditions. One of the central results of our analysis is that, for plateau-like potentials associated with the Higgs and Starobinsky models, inflation can be realized even for initial scalar field values which lie close to the minimum of the potential. This dispels a misconception relating to plateau potentials prevailing in the literature. We also find that inflation in all models is more robust for larger values of the initial energy scale.

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S. Mishra, V. Sahni and A. Toporensky
Wed, 17 Jan 18

Comments: 46 pages, 29 figures

Reconstructing warm inflation [CL]

The reconstruction of a warm inflationary universe model from the scalar spectral index $n_S(N)$ and the tensor to scalar ratio $r(N)$ as a function of the number of e-folds $N$ is studied. Under a general formalism we find the effective potential and the dissipative coefficient in terms of the cosmological parameters $n_S$ and $r$ considering the weak and strong dissipative stages under the slow roll approximation. As a specific example, we study the attractors for the index $n_S$ given by $n_{S}-1\propto N^{-1}$ and for the ratio $r\propto N^{-2}$, in order to reconstruct the model of warm inflation. Here, expressions for the effective potential $V(\phi)$ and the dissipation coefficient $\Gamma(\phi)$ are obtained.

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R. Herrera
Wed, 17 Jan 18

Comments: 23 pages and 2 figures

Singularities in Spherically Symmetric Solutions with Limited Curvature Invariants [CL]

We investigate static, spherically symmetric solutions in gravitational theories which have limited curvature invariants, aiming to remove the singularity in the Schwarzschild space-time. We find that if we only limit the Gauss-Bonnet term and the Ricci scalar, then the singularity at the origin persists. Moreover we find that the event horizon can develop a curvature singularity. We also investigate a new class of theories in which all components of the Riemann tensor are bounded. We find that the divergence of the quadratic curvature invariants at the event horizon is avoidable in this theory. However, other kinds of singularities due to the dynamics of additional degrees of freedom cannot be removed, and the space-time remains singular.

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D. Yoshida and R. Brandenberger
Wed, 17 Jan 18

Comments: 17 pages, 17 figures

Axionic Landscape for Higgs Near-Criticality [CL]

The measured value of the Higgs quartic coupling $\lambda$ is peculiarly close to the critical value above which the Higgs potential becomes unstable, when extrapolated to high scales by renormalization group running. It is tempting to speculate that there is an anthropic reason behind this near-criticality. We show how an axionic field can provide a landscape of vacuum states in which $\lambda$ scans. These states are populated during inflation to create a multiverse with different quartic couplings, with a probability distribution $P$ that can be computed. If $P$ is peaked in the anthropically forbidden region of Higgs instability, then the most probable universe compatible with observers would be close to the boundary, as observed. We discuss three scenarios depending on the Higgs vacuum selection mechanism: decay by quantum tunneling; by thermal fluctuations or by inflationary fluctuations.

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J. Cline and J. Espinosa
Fri, 12 Jan 18

Comments: 8 pages, 4 figures

Phase-transition sound of inflation at gravitational waves detectors [CEA]

It is well-known that the first-order phase transition (PT) will yield a stochastic gravitational waves (GWs) background with a logo-like spectrum. However, we show that when such a PT happened during the primordial inflation, the GWs spectrum brought by the PT will be reddened, which thus records the unique voiceprint of inflation. We assess the abilities of the GW detectors to detect the corresponding signal.

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Y. Wang, Y. Cai and Y. Piao
Fri, 12 Jan 18

Comments: 12 pages, 6figures