118471930
Equilateral non-Gaussianity from heavy fields
The effect of self-interactions of heavy scalar fields during inflation on the primordial non-Gaussianity is studied. We take a specific constant-turn quasi-single field inflation as an example. We derive an effective theory with emphasis on non-linear self-interactions of heavy fields and calculate the corresponding non-Gaussianity, which is of equilateral type and can be as relevant as those computed previously in the literature. We also derive the non-Gaussianity by directly using the in-in formalism, and verify the equivalence of these two approaches.
118608368
Scale invariant power spectrum in Hořava-Lifshitz cosmology without matter
In this paper we investigate the physical implications of the dynamical scalar mode in pure Hořava-Lifshitz gravity on cosmology. We find that it can produce a scale-invariant power spectrum in UV era if the detailed balance condition on the action is relaxed. This indicates that the physical scalar mode may seed the large scale structure and Hořava-Lifshitz cosmology could be a qualified alternative to inflationary scenario.
119250849
Power spectra of scalar and tensor modes in modified Horava-Lifshitz gravity
In Horava-Lifshitz gravity, the extra dynamical scalar mode could play significant role in cosmology. However it has been pointed out that such a scalar may suffer from the strong coupling problem in IR. We address this issue in this paper. Our analysis shows that the scalar mode could decouple naturally at \lambda=1 due to the extra gauge symmetry. On the other hand, the fact that the scalar mode becomes ghost when 1/3<\lambda<1 is a real challenge to the theory. We try to overcome this problem by modifying the action such that the RG flow lies outside the problematic region. We discuss the cosmological implications of the action and calculate the power spectra of scalar and tensor modes.
119238882
On the possibility of blue tensor spectrum within single field inflation
We present a series of theoretical constraints on the potentially viable inflation models that might yield a blue spectrum for primordial tensor perturbations. By performing a detailed dynamical analysis we show that, while there exists such possibility, the corresponding phase space is strongly bounded. Our result implies that, in order to achieve a blue tilt for inflationary tensor perturbations, one may either construct a non-canonical inflation model delicately, or study the generation of primordial tensor modes beyond the standard scenario of single slow-roll field.
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.
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.
118697879
TIME DEPENDENT VARIATIONAL PRINCIPLE FOR QUANTUM DYNAMICS IN THE SCHRODINGER PICTURE
Starting with the exact variational formulation of quantum mechanics (or quantum field theory) in the Schroedinger picture, and using Gaussian trail wave functions, an exact functional Schroedinger equation is obtained. The time-dependent Hartree-Fock approximation is obtained and extended to many oscillators and to field theory. The problem of quantum roll, in which an initial Gaussian wave packet starting at an unstable classical equilibrium point evolves in time, is treated using this formalism. Quantum tunnelling is also studied. (LEW)
116907392
COSMOLOGICAL CONSTRAINTS ON WITTEN'S HIERARCHY MECHANISM
In Witten’s hierarchical supersymmetric model the SU(5) symmetry stays unbroken until the temperature becomes of order of the fundamental scale, M, of the model. This together with other phenomenological constraints suggests that M must satisfy the Weinberg bound M ≳ 1011 GeV. Baryon number generation and primordial monopole density pose difficulties for the model.
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.
119984013
Effects of transverse beam polarization on anomalous. mu. --e events
We present differential cross sections, in the colliding-beam rest frame, for ..mu..--e pair production by leptonic decays of (a) heavy-spin-1/2-lepton pair, (b) spin-1-boson pair, themselves produced via one quantum annihilation. We find that study of the anomalous ..mu..--e events in the polarized e/sup +/e/sup -/ collisions is quite useful in understanding the dynamics behind these events. (AIP)
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.