The stochastic approach to inflation relies on one key assumption, the emergence of a long-wave classical field that drives the inflation and is subject to a shortwave classical noise. In this work we consider explicitly the potential that acts on the inflaton field, and analyze classicality conditions that must be satisfied to have an effective classical stochastic approach. When these hold, the dynamics is given by a two-dimensional classical Fokker-Planck equation. We develop some examples, already widely considered in different approaches, and find a very suggestive result, which is the damping of the quantum fluctuations by the effect of the inflaton interaction potential. ͓S0556-2821͑96͒01624-4͔PACS number͑s͒: 98.80.Cq, 04.62.ϩv PHYSICAL REVIEW D

Anisotropic neutrino emission during the neutron star formation can be the origin of the observed proper motions of pulsars. We derive a general expression for the momentum asymmetry in terms of the neutrino energy flux gradient, and show that a nonvanishing effect is induced at the lowest order by a deformed neutrinosphere. In particular, this result is valid for a neutrino flux transported through a spherical atmosphere with constant luminosity.Comment: 11 pages, added appendix, references, and minor changes in section 1, 2, and

We show that the parent Lagrangian method gives a natural generalization of the dual theories concept for non p-form fields. Using this generalization we construct here a three-parameter family of Lagrangians that are dual to the Fierz-Pauli description of a free massive spin-two system. The dual field is a three-index tensor T (µν)ρ , which dinamically belongs to the (2, 1) representation of the Lorentz group. As expected, the massless limit of our Lagrangian, which is parameter independent, has two propagating degrees of freedom per space point.interchanges dynamical equations with Bianchi identities, giving a full correspondence between both descriptions.An important predecessor of the modern approach to duality is the electric-magnetic symmetry ( E + i B) → e iφ ( E + i B) of the free Maxwell equations. When there are charged sources this symmetry can be maintained by introducing magnetic monopoles [5]. This transformation provides a connection between weak and strong couplings via the Dirac quantization condition. At the level of Yang-Mills theories with spontaneous symmetry breaking this kind of duality is expected, due to the existence of topological dyon-type solitons [6]. The extension of electromagnetic duality to SL(2, Z) is usually referred to as S-duality, and plays an important role in the non-perturbative study of field and string theories [7].These basic ideas have been subsequently generalized to arbitrary forms in arbitrary dimensions. Well known dualities are the ones between massless p -forms and (d − p − 2)forms fields and between massive p and (d − p − 1)-forms in d dimensional space-time [8]. These dualities among free fields have been proved using parent Lagrangians [9] as well as the canonical formalism [10]. They can be extended to include source interactions [11].The above duality among forms can be understood as a relation between fields in different representations of the Lorentz group. The origin of this equivalence can be traced using the little group technique for constructing the representations of the Poincare group in d dimensions. Given a standard momentum for a massive or a massless particle, the actual degrees of freedom are determined by its spin components, which are given by the irreducible representations of SO(d − 1) and SO(d − 2) respectively. These are expressed by traceless tensors with a definite permutation symmetry characterized by the Young diagrams. For the orthogonal groups O(n), the sum of the lengths of the first two columns of the Young diagrams is constrained to be less than or equal to n. Two Young diagrams having their first column of length l and n − l respectively, with the rest of the diagrams being identical, are called associated. For the group SO(n) associated Young diagrams correspond to the same representation [12]. The existence of two different tensorial realizations for one irreducible spin representation suggests that we can construct two theories with fields of different tensorial character for the same physical system. The relation between tw...

We develop a thorough description of neutrino oscillations in a magnetized protoneutron star, based on a resonance layer for neutrinos with different momentum directions. We apply our approach to the calculation of the asymmetry in the neutrino emission during the birth of a neutron star and the pulsar acceleration in the case of an active-sterile neutrino resonant conversion.The observed velocities can be obtained with the magnetic fields expected in the interior of a protoneutron star, for sterile neutrino masses of the order of KeV and small mixing angles. * Permanent address: Instituto Balseiro and CAB, Universidad Nacional de Cuyo and CNEA, 8400 Bariloche, Argentina 1

A generalization of duality transformations for arbitrary Lorentz tensors is presented, and a systematic scheme for constructing the dual descriptions is developed. The method, a purely Lagrangian approach, is based on a first order parent Lagrangian, from which the dual partners are generated. In particular, a family of theories which are dual to the massive spin two Fierz-Pauli field hµν , both free and coupled to an external source, is constructed in terms of a T (µν)σ tensor.

We develop a detailed analysis of synchrotron radiation in the effective Lorentz invariance violating (LIV) model of Myers-Pospelov, considering explicitly both the dynamics of the charge producing the radiation and the dynamics of the electromagnetic field itself. Within the radiation approximation we compute exact expressions in the LIV parameters for the electric and magnetic fields, the angular distribution of the power spectrum, the total emitted power in the m-th harmonic and the polarization. We also perform expansions of the exact results in terms of the LIV parameters to identify the dominant effects, and study the main features of the high energy limit of the spectrum. A very interesting consequence is the appearance of rather unexpected and large amplifying factors associated with the LIV effects, which go along with the usual contributions of the expansion parameter. This opens up the possibility of looking for astrophysical sources where these amplifying factors are important to further explore the constraints imposed upon the LIV parameters by synchrotron radiation measurements. We briefly sketch some phenomenological applications in the case of SNRs and GRBs.

The construction of dual theories for linearized gravity in four dimensions is considered. Our approach is based on the parent Lagrangian method previously developed for the massive spintwo case, but now considered for the zero mass case. This leads to a dual theory described in terms of a rank two symmetric tensor, analogous to the usual gravitational field, and an auxiliary antisymmetric field. This theory has an enlarged gauge symmetry, but with an adequate partial gauge fixing it can be reduced to a gauge symmetry similar to the standard one of linearized gravitation. We present examples illustrating the general procedure and the physical interpretation of the dual fields. The zero mass case of the massive theory dual to the massive spin-two theory is also examined, but we show that it only contains a spin-zero excitation.

After imposing the Gauss law constraint as an initial condition upon the Hilbert space of the Nambu model, in all its generic realizations, we recover QED in the corresponding nonlinear gauge A A ¼ n 2 M 2 . Our result is nonperturbative in the parameter M for n 2 Þ 0 and can be extended to the n 2 ¼ 0 case. This shows that, in the Nambu model, spontaneous Lorentz symmetry breaking dynamically generates gauge invariance, provided the Gauss law is imposed as an initial condition. In this way, electrodynamics is recovered, with the photon being realized as the Nambu-Goldstone modes of the spontaneously broken symmetry, which finally turns out to be nonobservable.