117951510
Parametric resonance with multi‐frequencies in preheating
We present here an extended abstract of the results derived in [1], We study the decay of the inflaton field to another scalar field χ in the parametric resonance preheating mechanism. We consider the presence of several simultaneous couplings between the fields. We show that the contribution for the χ field energy density of the higher harmonic is a small fraction of that of the fundamental frequency, and so the presence of a finite number of higher harmonics has limited cosmological implications
18454632
Scaling solutions from interacting fluids
We examine the dynamical implications of an interaction between some of the fluid components of the universe. We consider the combination of three matter components, one of which is a perfect fluid and the other two are interacting. The interaction term generalizes the cases found in scalar field cosmologies with an exponential potential. We find that attracting scaling solutions are obtained in several regions of parameter space, that oscillating behaviour is possible, and that new curvature scaling solutions exist. We also discuss the inflationary behaviour of the solutions and present some of the constraints on the strength of the coupling, namely those arising from nucleosynthesis.
121292064
General relativity as a cosmological attractor of scalar-tensor gravity theories
Abstract We investigate the relaxation of general scalar-tensor gravity theories towards general relativity. We extend Damour and Nordtvedt's work [Phys. Rev. Lett. 70 (1993) 2217; Phys. Rev. D 48 (1993) 3436] by including a cosmological potential. We find that Einstein's gravity is indeed a cosmological attractor both for isotropic and anisotropic universes, and that the universe exhibits inflationary expansion during the relaxation process.
119448124
BULK VISCOSITY IMPACT ON THE SCENARIO OF WARM INFLATION
The decay of the inflaton into radiation and particles during the slow-roll suggests that these may interact with each other and that the latter may also decay into subproducts before inflation is completed. As a consequence, the fluid is no longer perfect and a nonnegligible bulk viscosity necessarily sets in. We write the corresponding equations as an autonomous system and study the asymptotic behavior, the conditions for the existence of scaling solutions, and show that the late time effect of fluid dissipation alleviates the depletion of matter and increases the duration of inflation.
119090338
On the potentials yielding cosmological scaling solutions
In the present work we perform a phase-plane analysis of the complete dynamical system corresponding to a flat FRW cosmological models with a perfect fluid and a self-interacting scalar field and show that every positive and monotonous potential which is asymptotically exponential yields a scaling solution as a global attractor.
119519761
SCALAR FIELD PHASE DYNAMICS IN PREHEATING
We study the model of a massive inflaton field $\phi$ coupled to another scalar filed $\chi$ with interaction term $g^2\phi^2\chi^2$ for the first stage of preheating. We obtain the the behavior of the phase in terms of the iteration of a simple family of circle maps. When expansion of the universe is taken into account the qualitative behavior of the phase and growth number evolution is reminiscent of the behavior found in the case without expansion.
8883252
Observation of a New Narrow Axial-Vector Meson a1(1420).
The COMPASS Collaboration at CERN has measured diffractive dissociation of 190  GeV/c pions into the π(-)π(-)π(+) final state using a stationary hydrogen target. A partial-wave analysis (PWA) was performed in bins of 3π mass and four-momentum transfer using the isobar model and the so far largest PWA model consisting of 88 waves. A narrow peak is observed in the f0(980)π channel with spin, parity and C-parity quantum numbers J(PC)=1(++). We present a resonance-model study of a subset of the spin-density matrix selecting 3π states with J(PC)=2(++) and 4(++) decaying into ρ(770)π and with J(PC)=1(++) decaying into f0(980)π. We identify a new a1 meson with mass (1414(-13)(+15))  MeV/c2 and width (153(-23)(+8))  MeV/c2. Within the final states investigated in our analysis, we observe the new a1(1420) decaying only into f0(980)π, suggesting its exotic nature.
118474758
Analytic models for the evolution of semilocal string networks
We revisit previously developed analytic models for defect evolution and adapt them appropriately for the study of semilocal string networks. We thus confirm the expectation (based on numerical simulations) that linear scaling evolution is the attractor solution for a broad range of model parameters. We discuss in detail the evolution of individual semilocal segments, focusing on the phenomenology of segment growth, and also provide a preliminary comparison with existing numerical simulations.
115300255
On the theory of the invisible arion
Models with an ''invisible'' arion, a massless Goldstone particle interacting weakly with quarks and leptons, are considered. The coupling constant with photons, which is needed for the occurrence of arion--photon oscillations in an external magnetic field, is estimated.
118504596
Longitudinal double spin asymmetry $A_1^p$ and spin-dependent structure function $g_1^p$ of the proton at low $x$ and low $Q^2$ from COMPASS
The COMPASS experiment at CERN has collected a large sample of events of inelastic scattering of longitudinally polarised muons off longitudinally polarised protons in the non-perturbative region (four-momentum transfer squared $Q^2<1$ GeV$^2$/$c^2$), with a Bjorken scaling variable in the range $4\times 10^{-5}<x<4\times 10^{-2}$. The data set is two orders of magnitude larger than the similar sample collected by the SMC experiment. These data complement our data for polarised deuterons. They allow the accurate determination of the longitudinal double spin asymmetry $A_1^p$ and of the spin-dependent structure function $g_1^p$ of the proton in the region of low $x$ and low $Q^2$. The preliminary results of the analysis of these data yield non zero and positive asymmetries and of the structure function $g_1^p$. This is the first time that spin effects are observed at such low $x$.