Primordial spectral indices from generalized Einstein theories.
Primordial spectral indices are calculated to second order in slow-roll parameters for three closely related models of inflation, all of which contain a scalar field nonminimally coupled to the Ricci curvature scalar. In most cases, ${\mathit{n}}_{\mathit{s}}$ may be written as a function of the nonminimal curvature coupling strength \ensuremath{\xi} alone, with ${\mathit{n}}_{\mathit{s}}$(\ensuremath{\xi})\ensuremath{\le}1, although the constraints on \ensuremath{\xi} differ greatly between ``new inflation'' and ``chaotic inflation'' initial conditions. Under ``new inflation'' initial conditions, there are discrepancies between the values of ${\mathit{n}}_{\mathit{s}}$ as calculated in the Einstein frame and the Jordan frame. The sources for these discrepancies are addressed, and shown to have negligible effects on the numerical predictions for ${\mathit{n}}_{\mathit{s}}$. No such discrepancies affect the calculations under ``chaotic inflation'' initial conditions.

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: 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: 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: 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: 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.