57 research outputs found
Astrophysical and Cosmological Implications of Large Volume String Compactifications
We study the spectrum, couplings and cosmological and astrophysical
implications of the moduli fields for the class of Calabi-Yau IIB string
compactifications for which moduli stabilisation leads to an exponentially
large volume V ~ 10^{15} l_s^6 and an intermediate string scale m_s ~
10^{11}GeV, with TeV-scale observable supersymmetry breaking. All K\"ahler
moduli except for the overall volume are heavier than the susy breaking scale,
with m ~ ln(M_P/m_{3/2}) m_{3/2} ~ (\ln(M_P/m_{3/2}))^2 m_{susy} ~ 500 TeV and,
contrary to standard expectations, have matter couplings suppressed only by the
string scale rather than the Planck scale. These decay to matter early in the
history of the universe, with a reheat temperature T ~ 10^7 GeV, and are free
from the cosmological moduli problem (CMP). The heavy moduli have a branching
ratio to gravitino pairs of 10^{-30} and do not suffer from the gravitino
overproduction problem. The overall volume modulus is a distinctive feature of
these models and is an M_{planck}-coupled scalar of mass m ~ 1 MeV and subject
to the CMP. A period of thermal inflation can help relax this problem. This
field has a lifetime ~ 10^{24}s and can contribute to dark matter. It may be
detected through its decays to 2\gamma or e^+e^-. If accessible the e^+e^-
decay mode dominates, with Br(\chi \to 2 \gamma) suppressed by a factor
(ln(M_P/m_{3/2}))^2. We consider the potential for detection of this field
through different astrophysical sources and find that the observed gamma-ray
background constrains \Omega_{\chi} <~ 10^{-4}. The decays of this field may
generate the 511 keV emission line from the galactic centre observed by
INTEGRAL/SPI.Comment: 31 pages, 2 figures; v2. refs adde
Multifield Dynamics in Higgs-otic Inflation
In Higgs-otic inflation a complex neutral scalar combination of the and
MSSM Higgs fields plays the role of inflaton in a chaotic fashion. The
potential is protected from large trans-Planckian corrections at large inflaton
if the system is embedded in string theory so that the Higgs fields parametrize
a D-brane position. The inflaton potential is then given by a DBI+CS D-brane
action yielding an approximate linear behaviour at large field. The inflaton
scalar potential is a 2-field model with specific non-canonical kinetic terms.
Previous computations of the cosmological parameters (i.e. scalar and tensor
perturbations) did not take into account the full 2-field character of the
model, ignoring in particular the presence of isocurvature perturbations and
their coupling to the adiabatic modes. It is well known that for generic
2-field potentials such effects may significantly alter the observational
signatures of a given model. We perform a full analysis of adiabatic and
isocurvature perturbations in the Higgs-otic 2-field model. We show that the
predictivity of the model is increased compared to the adiabatic approximation.
Isocurvature perturbations moderately feed back into adiabatic fluctuations.
However, the isocurvature component is exponentially damped by the end of
inflation. The tensor to scalar ratio varies in a region ,
consistent with combined Planck/BICEP results.Comment: 35 pages, 11 figure
Cosmological Evolution of Dirac-Born-Infeld Field
We investigate the cosmological evolution of the system of a
Dirac-Born-Infeld field plus a perfect fluid. We analyze the existence and
stability of scaling solutions for the AdS throat and the quadratic potential.
We find that the scaling solutions exist when the equation of state of the
perfect fluid is negative and in the ultra-relativistic limit.Comment: 9 pages, 1 figure, LaTeX2e, references added, accepted for
publication in JCA
Lectures on Cosmic Inflation and its Potential Stringy Realizations
These notes present a brief introduction to Hot Big Bang cosmology and Cosmic
Inflation, together with a selection of some recent attempts to embed inflation
into string theory. They provide a partial description of lectures presented in
courses at Dubrovnik in August 2006, at CERN in January 2007 and at Cargese in
August 2007. They are aimed at graduate students with a working knowledge of
quantum field theory, but who are unfamiliar with the details of cosmology or
of string theory.Comment: 68 pages, lectures given at Dubrovnik, Aug 2006; CERN, January 2007;
and Cargese, Aug 200
Prospects for constraining the shape of non-Gaussianity with the scale-dependent bias
We consider whether the non-Gaussian scale-dependent halo bias can be used
not only to constrain the local form of non-Gaussianity but also to distinguish
among different shapes. In particular, we ask whether it can constrain the
behavior of the primordial three-point function in the squeezed limit where one
of the momenta is much smaller than the other two. This is potentially
interesting since the observation of a three-point function with a squeezed
limit that does not go like the local nor equilateral templates would be a
signal of non-trivial dynamics during inflation. To this end we use the
quasi-single field inflation model of Chen and Wang as a representative
two-parameter model, where one parameter governs the amplitude of
non-Gaussianity and the other the shape. We also perform a model-independent
analysis by parametrizing the scale-dependent bias as a power-law on large
scales, where the power is to be constrained from observations. We find that
proposed large-scale structure surveys (with characteristics similar to the
dark energy task force stage IV surveys) have the potential to distinguish
among the squeezed limit behavior of different bispectrum shapes for a wide
range of fiducial model parameters. Thus the halo bias can help discriminate
between different models of inflation.Comment: 12 pages, 3 figures, v2. minor corrections to the text, matches JCAP
published versio
The matter power spectrum in redshift space using effective field theory
The use of Eulerian 'standard perturbation theory' to describe mass assembly in the early universe has traditionally been limited to modes with k <= 0.1 h/Mpc at z=0. At larger k the SPT power spectrum deviates from measurements made using N-body simulations. Recently, there has been progress in extending the reach of perturbation theory to larger k using ideas borrowed from effective field theory. We revisit the computation of the redshift-space matter power spectrum within this framework, including for the first time for the full one-loop time dependence. We use a resummation scheme proposed by Vlah et al. to account for damping of the baryonic acoustic oscillations due to large-scale random motions and show that this has a significant effect on the multipole power spectra. We renormalize by comparison to a suite of custom N-body simulations matching the MultiDark MDR1 cosmology. At z=0 and for scales k <~ 0.4 h/Mpc we find that the EFT furnishes a description of the real-space power spectrum up to ~ 2%, for the ell=0 mode up to ~ 5% and for the ell = 2, 4 modes up to ~ 25%. We argue that, in the MDR1 cosmology, positivity of the ell = 0 mode gives a firm upper limit of k ~ 0.74 h/Mpc for the validity of the one-loop EFT prediction in redshift space using only the lowest-order counterterm. We show that replacing the one-loop growth factors by their Einstein-de Sitter counterparts is a good approximation for the ell = 0 mode, but can induce deviations as large as 2% for the ell = 2, 4 modes. An accompanying software bundle, distributed under open source licenses, includes Mathematica notebooks describing the calculation, together with parallel pipelines capable of computing both the necessary one-loop SPT integrals and the effective field theory counterterms
Effects of Scale-Dependent Non-Gaussianity on Cosmological Structures
The detection of primordial non-Gaussianity could provide a powerful means to
test various inflationary scenarios. Although scale-invariant non-Gaussianity
(often described by the formalism) is currently best constrained by
the CMB, single-field models with changing sound speed can have strongly
scale-dependent non-Gaussianity. Such models could evade the CMB constraints
but still have important effects at scales responsible for the formation of
cosmological objects such as clusters and galaxies. We compute the effect of
scale-dependent primordial non-Gaussianity on cluster number counts as a
function of redshift, using a simple ansatz to model scale-dependent features.
We forecast constraints on these models achievable with forthcoming data sets.
We also examine consequences for the galaxy bispectrum. Our results are
relevant for the Dirac-Born-Infeld model of brane inflation, where the
scale-dependence of the non-Gaussianity is directly related to the geometry of
the extra dimensions.Comment: 43 pages, 9 figures; references added, submitted to JCAP; typo
corrected in Table 1, minor changes to the tex
Volume Modulus Inflation and the Gravitino Mass Problem
The Hubble constant during the last stages of inflation in a broad class of
models based on the KKLT mechanism should be smaller than the gravitino mass, H
<~ m_{3/2}. We point out that in the models with large volume of
compactification the corresponding constraint typically is even stronger, H <~
m_{3/2}^{3/2}, in Planck units. In order to address this problem, we propose a
class of models with large volume of compactification where inflation may occur
exponentially far away from the present vacuum state. In these models, the
Hubble constant during inflation can be many orders of magnitude greater than
the gravitino mass. We introduce a toy model describing this scenario, and
discuss its strengths and weaknesses.Comment: 24 pages, JHEP style; v2. refs adde
Exploring cosmic origins with CORE : Inflation
We forecast the scientific capabilities to improve our understanding of cosmic inflation of CORE, a proposed CMB space satellite submitted in response to the ESA fifth call for a medium-size mission opportunity. The CORE satellite will map the CMB anisotropies in temperature and polarization in 19 frequency channels spanning the range 60-600 GHz. CORE will have an aggregate noise sensitivity of 1.7 mu K.arcmin and an angular resolution of 5' at 200 GHz. We explore the impact of telescope size and noise sensitivity on the inflation science return by making forecasts for several instrumental configurations. This study assumes that the lower and higher frequency channels suffice to remove foreground contaminations and complements other related studies of component separation and systematic effects, which will be reported in other papers of the series "Exploring Cosmic Origins with CORE." We forecast the capability to determine key inflationary parameters, to lower the detection limit for the tensor-to-scalar ratio down to the 10(-3) level, to chart the landscape of single field slow-roll inflationary models, to constrain the epoch of reheating, thus connecting inflation to the standard radiation-matter dominated Big Bang era, to reconstruct the primordial power spectrum, to constrain the contribution from isocurvature perturbations to the 10(-3) level, to improve constraints on the cosmic string tension to a level below the presumptive GUT scale, and to improve the current measurements of primordial non-Gaussianities down to the f(NL)(local) <1 level. For all the models explored, CORE alone will improve significantly on the present constraints on the physics of inflation. Its capabilities will be further enhanced by combining with complementary future cosmological observations.Peer reviewe
Exploring Cosmic Origins with CORE: Survey requirements and mission design
Future observations of cosmic microwave background (CMB) polarisation havethe potential to answer some of the most fundamental questions of modernphysics and cosmology. In this paper, we list the requirements for a future CMBpolarisation survey addressing these scientific objectives, and discuss thedesign drivers of the CORE space mission proposed to ESA in answer to the "M5"call for a medium-sized mission. The rationale and options, and themethodologies used to assess the mission's performance, are of interest toother future CMB mission design studies. CORE is designed as a near-ultimateCMB polarisation mission which, for optimal complementarity with ground-basedobservations, will perform the observations that are known to be essential toCMB polarisation scienceand cannot be obtained by any other means than adedicated space mission
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