995 research outputs found
Supersymmetric Inflation with the Ordinary Higgs?
We consider a model of D-term inflation in which the inflaton coincides with
the standard Higgs doublet. Non-renormalizable terms are controlled by a
discrete R-symmetry of the superpotential. We consider radiative corrections to
the scalar potential and find that Higgs inflation in the slow-roll
approximation is viable and consistent with CMB data, although with a rather
large value of the non-renormalizable coupling involved.Comment: 7 pages, 1 figure, published version, comments and reference added,
typos and factor of 2 corrected
Predicting the cosmological constant with the scale-factor cutoff measure
It is well known that anthropic selection from a landscape with a flat prior
distribution of cosmological constant Lambda gives a reasonable fit to
observation. However, a realistic model of the multiverse has a physical volume
that diverges with time, and the predicted distribution of Lambda depends on
how the spacetime volume is regulated. We study a simple model of the
multiverse with probabilities regulated by a scale-factor cutoff, and calculate
the resulting distribution, considering both positive and negative values of
Lambda. The results are in good agreement with observation. In particular, the
scale-factor cutoff strongly suppresses the probability for values of Lambda
that are more than about ten times the observed value. We also discuss several
qualitative features of the scale-factor cutoff, including aspects of the
distributions of the curvature parameter Omega and the primordial density
contrast Q.Comment: 16 pages, 6 figures, 2 appendice
Boltzmann brains and the scale-factor cutoff measure of the multiverse
To make predictions for an eternally inflating "multiverse", one must adopt a
procedure for regulating its divergent spacetime volume. Recently, a new test
of such spacetime measures has emerged: normal observers - who evolve in pocket
universes cooling from hot big bang conditions - must not be vastly outnumbered
by "Boltzmann brains" - freak observers that pop in and out of existence as a
result of rare quantum fluctuations. If the Boltzmann brains prevail, then a
randomly chosen observer would be overwhelmingly likely to be surrounded by an
empty world, where all but vacuum energy has redshifted away, rather than the
rich structure that we observe. Using the scale-factor cutoff measure, we
calculate the ratio of Boltzmann brains to normal observers. We find the ratio
to be finite, and give an expression for it in terms of Boltzmann brain
nucleation rates and vacuum decay rates. We discuss the conditions that these
rates must obey for the ratio to be acceptable, and we discuss estimates of the
rates under a variety of assumptions.Comment: 32 pp, 2 figs. Modified to conform to the version accepted by Phys.
Rev. D. The last paragraph of Sec. V-A, about Boltzmann brains in Minkowski
space, has been significantly enlarged. Two sentences were added to the
introduction concerning the classical approximation and the hope of finding a
motivating principle for the measure. Several references were adde
Measure Problem for Eternal and Non-Eternal Inflation
We study various probability measures for eternal inflation by applying their
regularization prescriptions to models where inflation is not eternal. For
simplicity we work with a toy model describing inflation that can interpolate
between eternal and non-eternal inflation by continuous variation of a
parameter. We investigate whether the predictions of four different measures
(proper time, scale factor cutoff, stationary and causal {diamond}) change
continuously with the change of this parameter. We will show that {only} for
the stationary measure the predictions change continuously. For the proper-time
and the scale factor cutoff, the predictions are strongly discontinuous. For
the causal diamond measure, the predictions are continuous only if the stage of
the slow-roll inflation is sufficiently long.Comment: 9 pages, 4 figure
Holographic Multiverse
We explore the idea that the dynamics of the inflationary multiverse is
encoded in its future boundary, where it is described by a lower dimensional
theory which is conformally invariant in the UV. We propose that a measure for
the multiverse, which is needed in order to extract quantitative probabilistic
predictions, can be derived in terms of the boundary theory by imposing a UV
cutoff. In the inflationary bulk, this is closely related (though not
identical) to the so-called scale factor cutoff measure.Comment: 23 pages, 4 figures. Replaced to match published versio
Mode Spectrum of the Electromagnetic Field in Open Universe Models
We examine the mode functions of the electromagnetic field on spherically
symmetric backgrounds with special attention to the subclass which allows for
the foliation as open Friedmann-Lemaitre (FL) spacetime. It is well-known that
in certain scalar field theories on open FL background there can exist
so-called supercurvature modes, their existence depending on parameters of the
theory. Looking at specific open universe models, such as open inflation and
the Milne universe, we find that no supercurvature modes are present in the
spectrum of the electromagnetic field. This excludes the possibility for
superadiabatic evolution of cosmological magnetic fields within these models
without relying on new physics or breaking the conformal invariance of
electromagnetism.Comment: 6 pages, 1 figure; v2: minor revision, appendix added, accepted for
publication in MNRA
Measures for a Transdimensional Multiverse
The multiverse/landscape paradigm that has emerged from eternal inflation and
string theory, describes a large-scale multiverse populated by "pocket
universes" which come in a huge variety of different types, including different
dimensionalities. In order to make predictions in the multiverse, we need a
probability measure. In landscapes, the scale factor cutoff measure
has been previously shown to have a number of attractive properties. Here we
consider possible generalizations of this measure to a transdimensional
multiverse. We find that a straightforward extension of scale factor cutoff to
the transdimensional case gives a measure that strongly disfavors large amounts
of slow-roll inflation and predicts low values for the density parameter
, in conflict with observations. A suitable generalization, which
retains all the good properties of the original measure, is the "volume factor"
cutoff, which regularizes the infinite spacetime volume using cutoff surfaces
of constant volume expansion factor.Comment: 30 pages, 1 figure Minor revisions, reference adde
Running Inflation in the Standard Model
An interacting scalar field with largish coupling to curvature can support a
distinctive inflationary universe scenario. Previously this has been discussed
for the Standard Model Higgs field, treated classically or in a leading log
approximation. Here we investigate the quantum theory using renormalization
group methods. In this model the running of both the effective Planck mass and
the couplings is important. The cosmological predictions are consistent with
existing WMAP5 data, with 0.967 < n_s < 0.98 (for N_e = 60) and negligible
gravity waves. We find a relationship between the spectral index and the Higgs
mass that is sharply varying for m_h ~ 120-135 GeV (depending on the top mass);
in the future, that relationship could be tested against data from PLANCK and
LHC. We also comment briefly on how similar dynamics might arise in more
general settings, and discuss our assumptions from the effective field theory
point of view.Comment: 17 pages in Phys Lett B format, 5 figures; v3: updated to match
published version, includes new Appendix B on EF
The CMB and the measure of the multiverse
In the context of eternal inflation, cosmological predictions depend on the
choice of measure to regulate the diverging spacetime volume. The spectrum of
inflationary perturbations is no exception, as we demonstrate by comparing the
predictions of the fat geodesic and causal patch measures. To highlight the
effect of the measure---as opposed to any effects related to a possible
landscape of vacua---we take the cosmological model, including the model of
inflation, to be fixed. We also condition on the average CMB temperature
accompanying the measurement. Both measures predict a 1-point expectation value
for the gauge-invariant Newtonian potential, which takes the form of a
(scale-dependent) monopole, in addition to a related contribution to the
3-point correlation function, with the detailed form of these quantities
differing between the measures. However, for both measures both effects are
well within cosmic variance. Our results make clear the theoretical relevance
of the measure, and at the same time validate the standard inflationary
predictions in the context of eternal inflation.Comment: 28 pages; v2: reference added, some clarification
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