5,415 research outputs found
Hunting Down the Best Model of Inflation with Bayesian Evidence
We present the first calculation of the Bayesian evidence for different
prototypical single field inflationary scenarios, including representative
classes of small field and large field models. This approach allows us to
compare inflationary models in a well-defined statistical way and to determine
the current "best model of inflation". The calculation is performed numerically
by interfacing the inflationary code FieldInf with MultiNest. We find that
small field models are currently preferred, while large field models having a
self-interacting potential of power p>4 are strongly disfavoured. The class of
small field models as a whole has posterior odds of approximately 3:1 when
compared with the large field class. The methodology and results presented in
this article are an additional step toward the construction of a full numerical
pipeline to constrain the physics of the early Universe with astrophysical
observations. More accurate data (such as the Planck data) and the techniques
introduced here should allow us to identify conclusively the best inflationary
model.Comment: 12 pages, 2 figures, uses RevTeX. Misprint corrected, references
added. Matches published versio
Testing Two-Field Inflation
We derive semi-analytic formulae for the power spectra of two-field inflation
assuming an arbitrary potential and non-canonical kinetic terms, and we use
them both to build phenomenological intuition and to constrain classes of
two-field models using WMAP data. Using covariant formalism, we first develop a
framework for understanding the background field kinematics and introduce a
"slow-turn" approximation. Next, we find covariant expressions for the
evolution of the adiabatic/curvature and entropy/isocurvature modes, and we
discuss how the mode evolution can be inferred directly from the background
kinematics and the geometry of the field manifold. From these expressions, we
derive semi-analytic formulae for the curvature, isocurvature, and cross
spectra, and the spectral observables, all to second-order in the slow-roll and
slow-turn approximations. In tandem, we show how our covariant formalism
provides useful intuition into how the characteristics of the inflationary
Lagrangian translate into distinct features in the power spectra. In
particular, we find that key features of the power spectra can be directly read
off of the nature of the roll path, the curve the field vector rolls along with
respect to the field manifold. For example, models whose roll path makes a
sharp turn 60 e-folds before inflation ends tend to be ruled out because they
produce strong departures from scale invariance. Finally, we apply our
formalism to confront four classes of two-field models with WMAP data,
including doubly quadratic and quartic potentials and non-standard kinetic
terms, showing how whether a model is ruled out depends not only on certain
features of the inflationary Lagrangian, but also on the initial conditions.
Ultimately, models must possess the right balance of kinematical and dynamical
behaviors, which we capture in a set of functions that can be reconstructed
from spectral observables.Comment: Revised to match accepted PRD version: Improved discussion of
background kinematics and multi-field effects, added tables summarizing key
quantities and their links to observables, more detailed figures, fixed typos
in former equations (103) and (117). 49 PRD pages, 11 figure
Chaotic inflation, radiative corrections and precision cosmology
We employ chaotic (phi^2 and phi^4) inflation to illustrate the important
role radiative corrections can play during the inflationary phase. Yukawa
interactions of phi, in particular, lead to corrections of the form -kappa
phi^4 ln(phi/mu), where kappa>0 and mu is a renormalization scale. For
instance, phi^4 chaotic inflation with radiative corrections looks compatible
with the most recent WMAP (5 year) analysis, in sharp contrast to the tree
level case. We obtain the 95% confidence limits 2.4x10^-14<~kappa<~5.7x10^-14,
0.931<~n_s<~0.958 and 0.038<~r<~0.205, where n_s and r respectively denote the
scalar spectral index and scalar to tensor ratio. The limits for phi^2
inflation are kappa<~7.7x10^-15, 0.929<~n_s<~0.966 and 0.023<~r<~0.135. The
next round of precision experiments should provide a more stringent test of
realistic chaotic phi^2 and phi^4 inflation.Comment: 5 pages, 4 figures, 2 tables. v2: added comments and references. v3:
changed title, published versio
A Toy Model for Open Inflation
The open inflation scenario based on the theory of bubble formation in the
models of a single scalar field suffered from a fatal defect. In all the
versions of this scenario known so far, the Coleman-De Luccia instantons
describing the creation of an open universe did not exist. We propose a simple
one-field model where the CDL instanton does exist and the open inflation
scenario can be realized.Comment: 7 pages, 4 figures, revtex, a discussion of density perturbations is
extende
Analysis of inflationary cosmological models in gauge theories of gravitation
Inflationary homogeneous isotropic cosmological models filled by scalar
fields and ultrarelativistic matter are examined in the framework of gauge
theories of gravitation. By using quadratic scalar field potential numerical
analysis of flat, open and closed models is curried out. Properties of
cosmological models are investigated in dependence on indefinite parameter of
cosmological equations and initial conditions at a bounce. Fulfilled analysis
demonstrates regular character of all cosmological models.Comment: LaTeX2e, iopart class file, 12 pages, 19 figure
The Triple-Alpha Process and the Anthropically Allowed Values of the Weak Scale
In multiple-universe models, the constants of nature may have different
values in different universes. Agrawal, Barr, Donoghue and Seckel have pointed
out that the Higgs mass parameter, as the only dimensionful parameter of the
standard model, is of particular interest. By considering a range of values of
this parameter, they showed that the Higgs vacuum expectation value must have a
magnitude less than 5.0 times its observed value, in order for complex
elements, and thus life, to form. In this report, we look at the effects of the
Higgs mass parameter on the triple-alpha process in stars. This process, which
is greatly enhanced by a resonance in Carbon-12, is responsible for virtually
all of the carbon production in the universe. We find that the Higgs vacuum
expectation value must have a magnitude greater than 0.90 times its observed
value in order for an appreciable amount of carbon to form, thus significantly
narrowing the allowed region of Agrawal et al.Comment: 9 pages, 1 figur
Thermal background can solve the cosmological moduli problem
It is shown that the coherent field oscillation of moduli fields with weak or
TeV scale masses can dissipate its energy efficiently if they have a derivative
coupling to standard bosonic fields in a thermal state. This mechanism may
provide a new solution to the cosmological moduli problem in some special
situations.Comment: 4 pages. revised versio
First CMB Constraints on the Inflationary Reheating Temperature
We present the first Bayesian constraints on the single field inflationary
reheating era obtained from Cosmic Microwave Background (CMB) data. After
demonstrating that this epoch can be fully characterized by the so-called
reheating parameter, we show that it is constrained by the seven years
Wilkinson Microwave Anisotropies Probe (WMAP7) data for all large and small
field models. An interesting feature of our approach is that it yields lower
bounds on the reheating temperature which can be combined with the upper bounds
associated with gravitinos production. For large field models, we find the
energy scale of reheating to be higher than those probed at the Large Hadron
Collider, Ereh > 17.3 TeV at 95% of confidence. For small field models, we
obtain the two-sigma lower limits Ereh > 890 TeV for a mean equation of state
during reheating = -0.3 and Ereh > 390 GeV for = -0.2. The
physical origin of these constraints is pedagogically explained by means of the
slow-roll approximation. Finally, when marginalizing over all possible
reheating history, the WMAP7 data push massive inflation under pressure (p <
2.2 at 95% of confidence where p is the power index of the large field
potentials) while they slightly favor super-Planckian field expectation values
in the small field models.Comment: 18 pages, 15 figures, uses RevTeX. References added, matches
published versio
Observational tests of inflation with a field derivative coupling to gravity
A field kinetic coupling with the Einstein tensor leads to a gravitationally
enhanced friction during inflation, by which even steep potentials with
theoretically natural model parameters can drive cosmic acceleration. In the
presence of this non-minimal derivative coupling we place observational
constraints on a number of representative inflationary models such as chaotic
inflation, inflation with exponential potentials, natural inflation, and hybrid
inflation. We show that most of the models can be made compatible with the
current observational data mainly due to the suppressed tensor-to-scalar ratio.Comment: 11 pages, 5 figure
Quintessence and phantom cosmology with non-minimal derivative coupling
We investigate cosmological scenarios with a non-minimal derivative coupling
between the scalar field and the curvature, examining both the quintessence and
the phantom cases in zero and constant potentials. In general, we find that the
universe transits from one de Sitter solution to another, determined by the
coupling parameter. Furthermore, according to the parameter choices and without
the need for matter, we can obtain a Big Bang, an expanding universe with no
beginning, a cosmological turnaround, an eternally contracting universe, a Big
Crunch, a Big Rip avoidance and a cosmological bounce. This variety of
behaviors reveals the capabilities of the present scenario.Comment: 8 pages, 8 figure
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