126 research outputs found
Hybrid inflation along waterfall trajectories
We identify a new inflationary regime for which more than 60 e-folds are
generated classically during the waterfall phase occuring after the usual
hybrid inflation. By performing a bayesian Monte-Carlo-Markov-Chain analysis,
this scenario is shown to take place in a large part of the parameter space of
the model. When this occurs, the observable perturbation modes leave the Hubble
radius during waterfall inflation. The power spectrum of adiabatic
perturbations is red, possibly in agreement with CMB constraints. A particular
attention has been given to study only the regions for which quantum
backreactions do not affect the classical dynamics. Implications concerning the
preheating and the absence of topological defects in our universe are
discussed.Comment: 10 pages, 5 figures, section III-A on quantum backreactions more
detailed, comments on transverse field gradient contribution added, version
accepted for publication in Phys.Rev.
Slow Roll during the Waterfall Regime: The Small Coupling Window for SUSY Hybrid Inflation
It has recently been pointed out that a substantial amount of e-folds can
occur during the waterfall regime of hybrid inflation. Moreover, Kodama et.al.
have derived analytic approximations for the trajectories of the inflaton and
of the waterfall fields. Based on these, we derive here the consequences for F-
and D-term SUSY hybrid inflation: A substantial amount of e-folds may occur in
the waterfall regime, provided kappa << M^2/M_P^2, where kappa is the
superpotential coupling, M the scale of symmetry breaking and M_P the reduced
Planck mass. When this condition is amply fulfilled, a number of e-folds much
larger than N_e\approx60 can occur in the waterfall regime and the scalar
spectral index is then given by the expression found by Kodama et.al.
n_s=1-4/N_e. This value may be increased up to unity, if only about N_e e-folds
occur during the waterfall regime, such that the largest observable scale
leaves the horizon close to the critical point of hybrid inflation, what can be
achieved for kappa\approx10^(-13) and M\approx5x10^(12) GeV in F-term
inflation. Imposing the normalization of the power spectrum leads to a lower
bound on the scale of symmetry breaking.Comment: 14 pages, 4 figures, minor corrections, references added, accepted
for publication in Phys.Rev.
Massive Primordial Black Holes from Hybrid Inflation as Dark Matter and the seeds of Galaxies
In this paper we present a new scenario where massive Primordial Black Holes
(PBH) are produced from the collapse of large curvature perturbations generated
during a mild waterfall phase of hybrid inflation. We determine the values of
the inflaton potential parameters leading to a PBH mass spectrum peaking on
planetary-like masses at matter-radiation equality and producing abundances
comparable to those of Dark Matter today, while the matter power spectrum on
scales probed by CMB anisotropies agrees with Planck data. These PBH could have
acquired large stellar masses today, via merging, and the model passes both the
constraints from CMB distortions and micro-lensing. This scenario is supported
by Chandra observations of numerous BH candidates in the central region of
Andromeda. Moreover, the tail of the PBH mass distribution could be responsible
for the seeds of supermassive black holes at the center of galaxies, as well as
for ultra-luminous X-rays sources. We find that our effective hybrid potential
can originate e.g. from D-term inflation with a Fayet-Iliopoulos term of the
order of the Planck scale but sub-planckian values of the inflaton field.
Finally, we discuss the implications of quantum diffusion at the instability
point of the potential, able to generate a swiss-cheese like structure of the
Universe, eventually leading to apparent accelerated cosmic expansion.Comment: 17 pages, 5 figures, comments welcom
Hybrid Inflation: Multi-field Dynamics and Cosmological Constraints
The dynamics of hybrid models is usually approximated by the evolution of a
scalar field slowly rolling along a nearly flat valley. Inflation ends with a
waterfall phase, due to a tachyonic instability. This final phase is usually
assumed to be nearly instantaneous. In this thesis, we go beyond these
approximations and analyze the exact 2-field dynamics of hybrid models. Several
effects are put in evidence: 1) the possible slow-roll violations along the
valley induce the non existence of inflation at small field values. Provided
super-planckian fields, the scalar spectrum of the original model is red, in
agreement with observations. 2) The initial field values are not fine-tuned
along the valley but also occupy a considerable part of the field space
exterior to it. They form a structure with fractal boundaries. Using bayesian
methods, their distribution in the whole parameter space is studied. Natural
bounds on the potential parameters are derived. 3) For the original model,
inflation is found to continue for more than 60 e-folds along waterfall
trajectories in some part of the parameter space. The scalar power spectrum of
adiabatic perturbations is modified and is generically red, possibly in
agreement with CMB observations. Topological defects are conveniently stretched
outside the observable Universe. 4) The analysis of the initial conditions is
extended to the case of a closed Universe, in which the initial singularity is
replaced by a classical bounce. In the third part of the thesis, we study how
the present CMB constraints on the cosmological parameters could be ameliorated
with the observation of the 21cm cosmic background, by future giant
radio-telescopes. Forecasts are determined for a characteristic Fast Fourier
Transform Telescope, by using both Fisher matrix and MCMC methods.Comment: 218 pages, PhD thesis, June 201
Avoiding the blue spectrum and the fine-tuning of initial conditions in hybrid inflation
Hybrid inflation faces two well-known problems: the blue spectrum of the
non-supersymmetric version of the model and the fine-tuning of the initial
conditions of the fields leading to sufficient inflation to account for the
standard cosmological problems. They are investigated by studying the exact
two-fields dynamics instead of assuming slow-roll. When the field values are
restricted to be less than the reduced Planck mass, a non-negligible part of
the initial condition space (around 15% depending on potential parameters)
leads to successful inflation. Most of it is located outside the usual
inflationary valley and organized in continuous patterns instead of being
isolated as previously found. Their existence is explained and their properties
are studied. This shows that no excessive fine-tuning is required for
successful hybrid inflation. Moreover, by extending the initial condition space
to planckian-like or super-planckian values, inflation becomes generically
sufficiently long and can produce a red-tilted scalar power spectrum due to
slow-roll violations. The robustness of these properties is confirmed by
conducting our analysis on three other models of hybrid-type inflation in
various framework: "smooth" and "shifted" inflation in SUSY and SUGRA, and
"radion assisted" gauge inflation. A high percentage of successful inflation
for smooth hybrid inflation (up to 80%) is observed.Comment: 20 pages, 14 figures. Some refs added/updated. New results for Smooth
and Shifted hybrid models. To appear in PR
Non-Gaussianities and Curvature Perturbations from Hybrid Inflation
For the original hybrid inflation as well as the supersymmetric F-term and
D-term hybrid models, we calculate the level of non-gaussianities and the power
spectrum of curvature perturbations generated during the waterfall, taking into
account the contribution of entropic modes. We focus on the regime of mild
waterfall, in which inflation continues for more than about 60 e-folds N during
the waterfall. We find that the associated f_nl parameter goes typically from
f_nl \simeq -1 / N_exit in the regime with N >> 60, where N_exit is the number
of e-folds between the time of Hubble exit of a pivot scale and the end of
inflation, down to f_nl ~-0.3 when N \gtrsim 60, i.e. much smaller in magnitude
than the current bound from Planck. Considering only the adiabatic
perturbations, the power spectrum is red, with a spectral index n_s = 1 - 4 /
N_exit, in the case N >> 60, whereas in the case N \gtrsim 60, it increases up
to unity. Including the contribution of entropic modes does not change the
observable predictions in the first case. However, in the second case, they are
a relevant source for the power spectrum of curvature perturbations, of which
the amplitude increases by several orders of magnitudes and can lead to black
hole formation. We conclude that due to the important contribution of entropic
modes, the parameter space leading to a mild waterfall phase is excluded by CMB
observations for all the considered models.Comment: 17 pages, 5 figures, Phys.Rev.D versio
Numerical forecasts for lab experiments constraining modified gravity:The chameleon model
Current acceleration of the cosmic expansion leads to coincidence as well as fine-tuning issues in the framework of general relativity. Dynamical scalar fields have been introduced in response of these problems, some of them invoking screening mechanisms for passing local tests of gravity. Recent lab experiments based on atom interferometry in a vacuum chamber have been proposed for testing modified gravity models. So far only analytical computations have been used to provide forecasts. We derive numerical solutions for chameleon models that take into account the effect of the vacuum chamber wall and its environment. With this realistic profile of the chameleon field in the chamber, we refine the forecasts that were derived analytically. We finally highlight specific effects due to the vacuum chamber that are potentially interesting for future experimentsinfo:eu-repo/semantics/publishe
Primordial black holes and a common origin of baryons and dark matter
The origin of the baryon asymmetry of the Universe (BAU) and the nature of dark matter are two of the most challenging problems in cosmology. We propose a scenario in which the gravitational collapse of large inhomogeneities at the quark-hadron epoch generates both the baryon asymmetry and most of the dark matter in the form of primordial black holes (PBHs). This is due to the sudden drop in radiation pressure during the transition from a quark-gluon plasma to non-relativistic hadrons. The collapse to a PBH is induced by fluctuations of a light spectator scalar field in rare regions and is accompanied by the violent expulsion of surrounding material, which might be regarded as a sort of “primordial supernova”. The acceleration of protons to relativistic speeds provides the ingredients for efficient baryogenesis around the collapsing regions and its subsequent propagation to the rest of the Universe. This scenario naturally explains why the observed BAU is of order the PBH collapse fraction and why the baryons and dark matter have comparable densities. The predicted PBH mass distribution ranges from subsolar to several hundred solar masses. This is compatible with current observational constraints and could explain the rate, mass and low spin of the black hole mergers detected by LIGO-Virgo. Future observations will soon be able to test this scenari
Detecting planetary-mass primordial black holes with resonant electromagnetic gravitational-wave detectors
The possibility to detect gravitational waves (GW) from planetary-mass
primordial black hole (PBH) binaries with electromagnetic (EM) detectors of
high-frequency GWs is investigated. We consider two patented experimental
designs, based on the inverse Gertsenshtein effect, in which incoming GWs
passing through a static magnetic field induce EM excitations inside either a
TM cavity or a TEM waveguide. The frequency response of the detectors is
computed for post-newtonian GW waveforms. We find that such EM detectors based
on current technology may achieve a strain sensitivity down to , which generates an EM power variation of W. This allows
the detection of PBH binary mergers of mass around if they
constitute more than percent of the dark matter, as suggested by recent
microlensing observations. We envision that this class of detectors could also
be used to detect cosmological GW backgrounds and probe sources in the early
Universe at energies up to the GUT scale.Comment: 16 pages, 7 figure
Cosmology in the era of Euclid and the Square Kilometre Array
Theoretical uncertainties on non-linear scales are among the main obstacles
to exploit the sensitivity of forthcoming galaxy and hydrogen surveys like
Euclid or the Square Kilometre Array (SKA). Here, we devise a new method to
model the theoretical error that goes beyond the usual cut-off on small scales.
The advantage of this more efficient implementation of the non-linear
uncertainties is tested through a Markov-Chain-Monte-Carlo (MCMC) forecast of
the sensitivity of Euclid and SKA to the parameters of the standard
CDM model, including massive neutrinos with total mass , and to
3 extended scenarios, including 1) additional relativistic degrees of freedom
(CDM + + ), 2) a deviation from the
cosmological constant (CDM + + ), and 3) a time-varying
dark energy equation of state parameter (CDM + +
). We compare the sensitivity of 14 different
combinations of cosmological probes and experimental configurations. For Euclid
combined with Planck, assuming a plain cosmological constant, our method gives
robust predictions for a high sensitivity to the primordial spectral index
(), the Hubble constant
(), the total neutrino mass
(). Assuming dynamical dark energy we get
for the mass and for the equation of state parameters. The predicted
sensitivity to is mostly stable against the extensions of the
cosmological model considered here. Interestingly, a significant improvement of
the constraints on the extended model parameters is also obtained when
combining Euclid with a low redshift HI intensity mapping survey by SKA1,
demonstrating the importance of the synergy of Euclid and SKA.Comment: 50 pages, 11 figures, 8 tables. v2: improved treatment of neutrino.
v3: updated Euclid sensitivity settings, matches accepted versio
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