117214043
Cosmological perturbations in inflation with multiple sound speeds
Abstract We study a multi-field inflationary theory with separable Lagrangian, which has different speed of sound for each field. We find that the fields always coupled at perturbative level through gravitational interaction. We show that if the coupling terms among the perturbation fields are weak enough, these fields can be treated as a combination of decoupled fields, which are similar to normal modes in coupled oscillation. By virtue of such fields, the curvature perturbation at horizon crossing can be calculated up to the leading order of slow-variation parameters via δ N formalism. Explicitly, we consider a model of multi-speed DBI inflation, and calculate the power spectrum in detail. The result depends on the ratio of different speeds of sound, and shows an apparent amplification when the ratio deviates from unity.
118701741
Curvature perturbation spectrum in two-field inflation with a turning trajectory
We revisit a two-component inflaton model with a turning trajectory in the field space, where the field slowly rolls down along the trajectory. We consider the case when the effective mass in the direction perpendicular to the trajectory, namely the isocurvature direction, is either of the same order as or much larger than the Hubble parameter. Assuming that the turning angular velocity is small, we compute analytically the corrections to the power spectrum of curvature perturbation caused by the mediation of the heavy isocurvature perturbation, and compare our analytic results with the numerical ones. Especially, when Meff2 H2, we find that it is proportional to Meff−2. This result is consistent with the one obtained previously by an effective field theory approach.
118390460
1/R correction to gravity in the early universe
To explain the accelerated expansion of the late universe, the 1/R correction to Einstein gravity is usually considered, where R is the Ricci scalar. This correction term, if stable, is generally believed to be negligible during inflation. However, if the 1/R term is inflaton dependent, it will dramatically change the story of inflation. The entropy perturbation will naturally appear and drive the evolution of curvature perturbation outside the Hubble horizon. In a large class of models, the entropy perturbation can be made nearly scale invariant. In Einstein gravity the single-field inflation with a quartic potential has been ruled out by recent observations, but it revives when the 1/R term is turned on. The evolution of non-Gaussianities on a large scale are also studied and applied to inflation with 1/R correction. In some specific models, a large non-Gaussianity can be naturally generated outside the horizon. A recent study ruled out almost all f(R) models during the matter-dominated phase. Taking this into consideration, we are left with a limited class of model which recovers the Einstein gravity soon after reheating.
119157556
Inflation beyond T-models and primordial B-modes
Abstract We describe extended theories which shares the gauge transformation symmetry of the T-models, and takes the T-models as well as Starobinsky model as special cases. We derive a general relation between the two slow-roll parameters, and find that a large class of models can be embedded. Such models include more general Starobinsky-like inflation as well as the chaotic inflation with a large tensor-to-scalar ratio consistent with the BICEP2 result.
120641629
External Gravitational Interactions in Quantum Field Theory
Abstract We consider the renormalization of Green's functions of λφ 4 quantum field theory in an external gravitational field specified by the metric tensor g μν ( y ). Green's functions Γ ( n ,3) describing the interaction of j scalar particles to arbitrary order n in the gravitational field are shown to be made finite by the standard renormalizations of the flatspace theory and a renormalization of the coefficient of the improvement term in the action functional. These results in φ 4 theory can be extended to all renormalizable field theories.
120447542
Inflation-driving scalar field
Abstract The quantum mechanical behavior of the Higgs field which drives inflation of the early universe is discussed. The standard picture of the new inflationary universe cannot be realized in the minimal SU(5) model. A realistic model in which inflation is driven by a complex gauge singlet Higgs field containing the axion is presented.
118924784
Entanglement entropy of nontrivial states
Abstract We study the entanglement entropy arising from coherent states and one-particle states. We show that it is possible to define a finite entanglement entropy by subtracting the vacuum entropy from that of the considered states, when the unobserved region is the same.
122337528
Cosmological consequences of a hierarchical supersymmetric model
Abstract Unusual finite-temperature behavior of Witten's supersymmetric model is discussed. A high-temperature phase persists to the weak-interaction scale. Initial monopole density can be strongly suppressed and production of heavy particles is inhibited. Difficulties with baryon generation are suggested.
118360792
The behavior of the Higgs field in the new inflationary universe