119205686
Note on the stabilities of the lightlike Galileon solutions
Light-like galileon solutions have been used to investigate the chronology problem in galileon-like theories, and in some cases may also be considered as solitons, evading a non-existence constraint from a zero-mode argument. Their stabilities have been analyzed via "local" approximation, which appears to suggest that all these light-like solutions are stable. We re-analyze the stability problem by solving the linear perturbation equation \emph{exactly}, and point out that the finite energy condition is essential for the light-like solitons to be stable. We also clarify potential ghost instabilities and why the zero-mode argument can not be naively generalized to include the light-like solitons.
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.
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.
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.
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.
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.
118429759
A New barrier penetration formula and its application to alpha-decay half-lives
Starting from the WKB approximation, a new barrier penetration formula is proposed for potential barriers containing a long-range Coulomb interaction. This formula is especially proper for the barrier penetration with penetration energy much lower than the Coulomb barrier. The penetrabilities calculated from the new formula agree well with the results from the WKB method. As a first attempt, this new formula is used to evaluate α-decay half-lives of atomic nuclei and a good agreement with the experiment is obtained.
121706213
TeV LEPTOGENESIS IN THE MINIMAL SEESAW MODEL
We present a particularly economical and suggestive neutrino mass model, in which there are only two right-handed Majorana neutrinos of O(1) TeV and their masses are highly degenerate. Its novel Yukawa-coupling texture together with the seesaw mechanism allows us to achieve the normal neutrino mass hierarchy with ml = 0 and a nearly tri-bimaximal neutrino mixing pattern with the maximal CP-violating phase: eZ3 = n/4, 161 = ~ / 2 and sin2 = (1 -2 tan' eI3)/3. One may also obtain the inverted neutrino mass hierarchy with m3 = 0 and the corresponding neutrino mixing pattern with eZ3 = n/4 and eI3 = S = 0. In both cases, the observed matter-antimatter asymmetry of the Universe can naturally be interpreted through the resonant leptogenesis mechanism. An experimental test of this TeV-scale neutrino mass model might not be impossible at LHC and ILC in the near future.
119227150
Nonaxial-octupole Y-32 correlations in N=150 isotones from multidimensional constrained covariant density functional theories
The nonaxial reflection-asymmetric beta(32) shape in some transfermium nuclei with N = 150, namely, Cm-246, Cf-248, Fm-250, and No-252, are investigated with multidimensional constrained covariant density functional theories. By using the density-dependent point-coupling covariant density functional theory with the parameter set DD-PC1 in the particle-hole channel, it is found that, for the ground states of Cf-248 and Fm-250, the nonaxial octupole deformation parameter beta(32) > 0.03 and the energy gain due to the beta(32) distortion is larger than 300 keV. In Cm-246 and No-252, shallow beta(32) minima are found. The occurrence of the nonaxial octupole beta(32) correlations is mainly from a pair of neutron orbitals, [734]9/2 (nu j(15/2)) and [622]5/2 (nu g(9/2)), which are close to the neutron Fermi surface, and a pair of proton orbitals, [521]3/2 (pi f(7/2)) and [633]7/2 (pi i(13/2)), which are close to the proton Fermi surface. The dependence of the nonaxial octupole effects on the form of the energy density functional and on the parameter set is also studied.
119525752
First order shape transition and critical point nuclei in Sm isotopes from relativistic mean field approach
The critical point nuclei in Sm isotopes, which marks the first order phase transition between spherical U(5) and axially deformed shapes SU(3), have been investigated in the microscopic quadrupole constrained relativistic mean field (RMF) model plus BCS method with all the most used interactions, i.e., NL1, NL3, NLSH and TM1. The calculated potential energy surfaces show a clear shape transition for the even-even Sm isotopes with $N = 82\sim 96$ and the critical point nuclei are found to be $^{148}$Sm, $^{150}$Sm and $^{152}$Sm. Similar conclusions can also be drawn from the microscopic neutron and proton single particle spectra.
122981402
Behavior of one-quasiparticle levels in odd isotonic chains of heavy nuclei
The low-lying one-quasiparticle states are studied in the isotonic chains with N = 147, 149, 151, 153, and 155 within the microscopic-macroscopic and self-consistent approaches. The energies of one-quasiparticle states change rather smoothly in the isotonic chains if there is no cross of the proton subshell. The alpha-decay schemes of several nuclei are suggested. The isomeric states in the odd isotopes of Fm and No are discussed.