119273766
Gravitational waves from oscillon preheating
A bstractOscillons are long-lived, localized excitations of nonlinear scalar fields which may be copiously produced during preheating after inflation, leading to a possible oscillon dominated phase in the early Universe. For example, this can happen after axion monodromy inflation, on which we run our simulations. We investigate the stochastic gravitational wave background associated with an oscillon-dominated phase. An isolated oscillon is spherically symmetric and does not radiate gravitational waves, and we show that the flux of gravitational radiation generated between oscillons is also small. However, a significant stochastic gravitational wave background may be generated during preheating itself (i.e, when oscillons are forming), and in this case the characteristic size of the oscillons is imprinted on the gravitational wave power spectrum, which has multiple, distinct peaks.
119288312
Galileons with Gauge Symmetries
Galileon models arise in certain braneworld scenarios as modifications to General Relativity, and are also interesting as field theories in their own right. We show how the galileon model can be naturally generalized to include local gauge symmetries, by allowing for couplings to Yang-Mills fields. The resulting theories have at most second order spacetime derivatives in any representation of the gauge group, thereby avoiding Ostrogradski ghosts. We also extend the models to include curved space, and show how in that case we need to include non-minimal couplings between the galileons and the curvature tensors for the theory to retain its second order nature.
119117717
Gradient expansion of superhorizon perturbations in G-inflation
We develop the gradient expansion formalism for shift-symmetric Galileon-type actions. We focus on backgrounds that undergo inflation, work in the synchronous gauge, and obtain a general solution up to second order without imposing extra conditions at first order. The solution simplifies during the late stages of inflation. We also define a curvature perturbation conserved up to first order.
55434748
Multi-Galileons, solitons, and Derrick's theorem
The field theory Galilean symmetry, which was introduced in the context of modified gravity, gives a neat way to construct Lorentz-covariant theories of a scalar field, such that the equations of motion contain at most second-order derivatives. Here we extend the analysis to an arbitrary number of scalars, and examine the restrictions imposed by an internal symmetry, focussing in particular on SU(N) and SO(N). This therefore extends the possible gradient terms that may be used to stabilise topological objects such as sigma model lumps.
55684447
Cosmological constraints on f(G) dark energy models
Modified gravity theories with the Gauss-Bonnet term G = R2−4RμνRμν+RμνρσRμνρσ have recently gained a lot of attention as a possible explanation of dark energy. We perform a thorough phase space analysis on the so-called f(G) models, where f(G) is some general function of the Gauss-Bonnet term, and derive conditions for the cosmological viability of f(G) dark energy models. Following the f(R) case, we show that these conditions can be nicely presented as geometrical constraints on the derivatives of f(G). We find that for general f(G) models there are two kinds of stable accelerated solutions, a de Sitter solution and a phantom-like solution. They co-exist with each other and which solution the universe evolves to depends on the initial conditions. Finally, several toy models of f(G) dark energy are explored. Cosmologically viable trajectories that mimic the ΛCDM model in the radiation and matter dominated periods, but have distinctive signatures at late times, are obtained.
118686993
Bi-galileon theory II: phenomenology
We continue to introduce bi-galileon theory, the generalisation of the single galileon model introduced by Nicolis et al. The theory contains two coupled scalar fields and is described by a Lagrangian that is invariant under Galilean shifts in those fields. This paper is the second of two, and focuses on the phenomenology of the theory. We are particularly interesting in models that admit solutions that are asymptotically self accelerating or asymptotically self tuning. In contrast to the single galileon theories, we find examples of self accelerating models that are simultaneously free from ghosts, tachyons and tadpoles, able to pass solar system constraints through Vainshtein screening, and do not suffer from problems with superluminality, Cerenkov emission or strong coupling. We also find self tuning models and discuss how Weinberg’s no go theorem is evaded by breaking Poincaré invariance in the scalar sector. Whereas the galileon description is valid all the way down to solar system scales for the self-accelerating models, unfortunately the same cannot be said for self tuning models owing to the scalars backreacting strongly on to the geometry.
1737359
Determination of the initial flavor composition of ultrahigh-energy neutrino fluxes with neutrino telescopes
We propose a simple but useful parametrization of the flavor composition of ultrahigh-energy neutrino fluxes produced from distant astrophysical sources: phi(e)phi(mu)phi(tau)=sin(2)xi cos(2)zeta cos(2)xi cos(2)zeta sin(2)zeta. We show that it is possible to determine or constrain xi and zeta by observing two independent neutrino flux ratios at the second-generation neutrino telescopes, provided three neutrino mixing angles and the Dirac CP-violating phase have been well measured in neutrino oscillations. Any deviation of zeta from zero will signify the existence of cosmic nu(tau) and (nu) over bar (tau) neutrinos at the source, and an accurate value of xi can be used to test both the conventional mechanism and the postulated scenarios for cosmic neutrino production.
121139162
High-spin states in (156)Yb and structure evolutions at large angular momenta in even-A Yb isotopes
High-spin states of (156)Yb have been studied via the (144)Sm((16)O,4n)(156)Yb fusion-evaporation reaction at beam energy 102 MeV. The positive-parity yrast band and negative-parity cascade have been extended up to higher-spin states, respectively. In the present work, the negative-parity sequence above the 25(-) state was found to be irregular and fragment into many parallel branches. This pattern may related to the excitation from the nucleon in the Z=64,N=82 core. The characteristics of alignment plot and E-GOS curve for the positive-parity yrast sequence in (156)Yb indicate that this nucleus may undergo an evolution from quasivibrational to quasirotational structure with increasing angular momentum. Based on a systematic summary of the available experimental alignments for the even-A (156,158,160,162,164)Yb isotopes, the structural evolutions induced by the increase in angular momentum, as well as by the change in neutron numbers, in these even-A Yb isotopes have been discussed in comparison with the cranked Woods-Saxon-Strutinsky calculations by means of total-Routhian-surface (TRS) methods.
119114319
Texture Zeros for Dirac Neutrinos and Current Experimental Tests
The Daya Bay and RENO reactor neutrino experiments have revealed that the smallest neutrino mixing angle is in fact relatively large, i.e. θ13 ≈9°. Motivated by this exciting progress, we perform a systematic study of the neutrino mass matrix Mν with one or two texture zeros, in the assumption that neutrinos are Dirac particles. Among 15 possible patterns with two texture zeros, only three turn out to be favored by current neutrino oscillation data at the 3σ level. Although all the six patterns with one texture zero are compatible with the experimental data at the 3σ level, the parameter space of each pattern is strictly constrained. Phenomenological implications of Mν on the leptonic CP violation and neutrino mass spectrum are explored, and the stability of texture zeros against the radiative corrections is also discussed.
119479559
Analytic continuation of single-particle resonance energy and wave function in relativistic mean field theory
Single-particle resonant states in spherical nuclei are studied by an analytic continuation in the coupling constant (ACCC) method within the framework of the self-consistent relativistic mean field (RMF) theory. Taking the neutron resonant state nu1g(9/2) in Ca-60 as an example, we examine the analyticity of the eigenvalue and eigenfunction for the Dirac equation with respect to the coupling constant by means of a Pade approximant of the second kind. The RMF-ACCC approach is then applied to Zr-122 and, for the first time, this approach is employed to investigate both the energies, widths, and wave functions for lnot equal0 resonant states close to the continuum threshold. Predictions are also compared with corresponding results obtained from the scattering phase shift method.
118108616
Proton magic even-even isotopes and giant halos of Ca isotopes with relativistic continuum Hartree-Bogoliubov theory
We study the proton magic O, Ca, Ni, Zr, Sn, and Pb isotope chains from the proton drip line to the neutron drip line with the relativistic continuum Hartree-Bogoliubov (RCHB) theory. Particulary, we study in detail the properties of even-even Ca isotopes due to the appearance of giant halos in neutron rich Ca nuclei near the neutron drip line. The RCHB theory is able to reproduce the experimental binding energiesEb and two neutron separation energiesS2n very well. The predicted neutron drip line nuclei are28O,72Ca,98Ni,136Zr,176Sn, and266Pb. Halo and giant halo properties predicted in Ca isotopes withA>60 are investigated in detail through analysis of two neutron separation energies, nucleon density distributions, single particle energy levels, and the occupation probabilities of energy levels including continuum states. The spin-orbit splitting and the diffuseness of nuclear potential in these Ca isotopes, as well as the neighboring lighter isotopes in the drip line Ca region and find certain possibilities of giant halo nuclei in the Ne−Na−Mg drip line nuclei are also studied.