Post-inflation reheating in an expanding universe.
An analytic means of studying the resonant decay of the inflaton field is developed for the case of background expansion H # 0. It is shown that the parametric resonance in the in0aton’s decay need not disappear when the expansion of the universe is taken into account, although the total number of particles produced is fewer than that in the H Y 0 case.

title: Conformal Transformations with Multiple Scalar Fields
abstract: Center for Theoretical Physics and Department of Physics,Massachusetts Institute of Technology,Cambridge, Massachusetts 02139 USA(Dated: April 26, 2010)Many interesting models incorporate scalar ﬁelds with non-minimal couplings tothe spacetime Ricci curvature scalar. As is well known, if only one scalar ﬁeld isnon-minimally coupled, then one may perform a conformal transformation to a newframe in which both the gravitational portion of the Lagrangian and the kinetic termfor the (rescaled) ﬁeld assume canonical form. We examine under what conditionsthe gravitational and kinetic terms in the Lagrangian may be brought into canonicalform when more than one scalar ﬁeld has non-minimal coupling. A particular classof two-ﬁeld models admits such a transformation, but models with more than twonon-minimally coupled ﬁelds in general do not.

title: Resonance Structure for Preheating with Massless Fields
abstract: We extend recent work on the resonance structure for post-inflation reheating, providing an analytic treatment for models in which both the inflaton and the fields into which it decays are massless. Solutions are derived which are valid for either a spatially-flat or spatially-open metric. Closed-form solutions are given for the characteristic exponent, which measures the rate of particle production during preheating. It is demonstrated that in certain ranges of parameter space, the maximum values of the characteristic exponent in an open universe are several times greater than the maximum values in a spatially-flat universe. It is further demonstrated that the solutions found here by means of a simple algebraic construction match the two previously-known exact solutions, which were derived in terms of special functions.

title: Restoring the sting to metric preheating
abstract: The relative growth of field and metric perturbations during preheating is sensitive to initial conditions set in the preceding inflationary phase. Recent work suggests this may protect super-Hubble metric perturbations from resonant amplification during preheating. We show that this possibility is fragile and sensitive to the specific form of the interactions between the inflaton and other fields. The suppression is naturally absent in two classes of preheating in which either: (1) the vacua of the noninflaton fields during inflation are deformed away from the origin; or (2) the effective masses of noninflaton fields during inflation are small but during preheating are large. Unlike the simple toy model of a g2Φ2χ2 coupling, most realistic particle physics models contain these other features. Moreover, they generically lead to both adiabatic and isocurvature modes and non-Gaussian scars on super-Hubble scales. Large-scale coherent magnetic fields may also appear naturally.

title: When fields collide.
abstract: Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters.

title: Inflationary Cosmology: Exploring the Universe from the Smallest to the Largest Scales
abstract: Understanding the behavior of the universe at large depends critically on insights about the smallest units of matter and their fundamental interactions. Inflationary cosmology is a highly successful framework for exploring these interconnections between particle physics and gravitation. Inflation makes several predictions about the present state of the universe—such as its overall shape, large-scale smoothness, and smaller scale structure—which are being tested to unprecedented accuracy by a new generation of astronomical measurements. The agreement between these predictions and the latest observations is extremely promising. Meanwhile, physicists are busy trying to understand inflation's ultimate implications for the nature of matter, energy, and spacetime.

title: Observation of the topological Aharonov-Casher phase shift by neutron interferometry.
abstract: The phase shift predicted by Aharonov and Casher for a magnetic dipole diffracting around a charged electrode has been observed for the case of thermal neutrons, using a neutron interferometer containing a 30-kV/mm vacuum electrode system. The judicious use of the Earth's gravitational field introduces a spin-independent phase shift which enables unpolarized neutrons to be used. A supplementary magnetic bias field of the correct magnitude allows first-order sensitivity to be achieved; even so, the theoretically predicted phase shift is only 1.50 mrad for the geometry and conditions of the experiment. We observe a phase shift of 2.19\ifmmode\pm\else\textpm\fi{}0.52 mrad.

title: Observation of the scalar Aharonov-Bohm effect by neutron interferometry.
abstract: Two calculations are presented that clarify how the density profile equilibrates near the liquid-vapor critical point. Both use the equation of heat transfer recently improved to account for the large compressibility near the critical point. Previous work by others indicated that in one dimension the slowest mode of this equation relaxes at a rate four times faster than that predicted by the older, usual equation of heat transfer. However, this is not always true in higher dimensions. The first calculation demonstrates this for the cases of isobaric modes excited by temperature gradients in a rectangle and in a thin disk. For thin experimental cells with isothermal walls the slowest mode is accurately estimated by the usual heat-transfer equation

title: Scalar Aharonov-Bohm experiment with neutrons.
abstract: The scalar version of the Aharonov-Bohm effect predicts a phase shift for de Broglie waves due to the action of a scalar potential in an otherwise field-free (i.e., force-free) region of space. Unlike the more familiar effect due to the magnetic vector potential, the scalar effect has hitherto remained unverified due, presumably, to technical difficulties in electron interferometry. Rather than using electrons acted on by electrostatic potentials, we have performed an analogous interferometry experiment with thermal neutorns subject to pulsed magnetic fields. The expected phase shifts have been observed to a high degree of accuracy.