22 research outputs found
Gravitational perturbations from oscillons and transients after inflation
We study the scalar and tensor perturbations generated by the fragmentation
of the inflaton condensate into oscillons or transients after inflation, using
nonlinear classical lattice simulations. Without including the backreaction of
metric perturbations, we find that the magnitude of scalar metric perturbations
never exceeds a few , whereas the maximal strength of the
gravitational wave signal today is for standard
post-inflationary expansion histories. We provide parameter scalings for the
-attractor models of inflation, which can be easily applied to other
models. We also discuss the likelihood of primordial black hole formation, as
well as conditions under which the gravitational wave signal can be at
observationally interesting frequencies and amplitudes.
Finally, we provide an upper bound on the frequency of the peak of the
gravitational wave signal, which applies to all preheating scenarios.Comment: 18 pages, 8 figure
The charged inflaton and its gauge fields: preheating and initial conditions for reheating
We calculate particle production during inflation and in the early stages of
reheating after inflation in models with a charged scalar field coupled to
Abelian and non-Abelian gauge fields. A detailed analysis of the power spectra
of primordial electric fields, magnetic fields and charge fluctuations at the
end of inflation and preheating is provided. We carefully account for the Gauss
constraints during inflation and preheating, and clarify the role of the
longitudinal components of the electric field. We calculate the timescale for
the back-reaction of the produced gauge fields on the inflaton condensate,
marking the onset of non-linear evolution of the fields. We provide a
prescription for initial conditions for lattice simulations necessary to
capture the subsequent nonlinear dynamics. On the observational side, we find
that the primordial magnetic fields generated are too small to explain the
origin of magnetic fields on galactic scales and the charge fluctuations are
well within observational bounds for the models considered in this paper.Comment: 48 pages, 6 figures, 2 appendices, v3: references added, minor
changes to text, to appear in JCA
Production and Backreaction of Fermions from Axion- Gauge Fields during Inflation
gauge fields and axions can have a stable, isotropic and homogeneous
configuration during inflation. However, couplings to other matter species lead
to particle production, which in turn induces backreaction on and
destabilization of the non-abelian and axion background. In this paper, we
first study the particle production by a gauge field coupled to a
massive Dirac doublet. To carry out this calculation we have made two technical
improvements compared to what has been done in the literature. First, we apply
the anti-symmetrization of the operators to treat particles and anti-particles
on equal footing, second, to deal with the UV divergences, we apply
instantaneous subtraction. We find that, the backreaction of produced fermions
on the background is negligible for model parameters of observational
interest. Next, we consider production of fermions due to coupling to the
axion. The tree-level backreaction on the gauge fields, as well as on the
axion, is vanishingly small. We also provide an estimate for the loop effects.Comment: Matches version accepted for publication in PR
Axion anomalies
We study fermions derivatively coupled to axion-like or pseudoscalar fields,
and show that the axial vector current of the fermions is not conserved in the
limit where the fermion is massless. This apparent violation of the classical
chiral symmetry is due to the background axion field. We compute the
contributions to this anomalous Ward identity due to the pseudoscalar field
alone, which arise in Minkowski space, as well as the effects due to an
interaction with an external gravitational field. For the case of massless
fermions, these interactions induce terms in the axion effective action that
can be removed by the addition of local counterterms. We demonstrate that these
counterterms are generated by the transformation of the path integral measure
when transforming the theory from a form where the chiral symmetry is manifest
to one where the symmetry is only apparent after using the classical equations
of motion. We work perturbatively in Minkowski space and include the effects of
interactions with a linearized gravitational field. Using the heat kernel
method, we study the transformation properties of the path integral measure,
and include the effects of non-linear gravity as well as interactions with
gauge fields. Finally, we verify our relation by considering derivatively
coupled fermions during pseudoscalar-driven inflation and computing the
divergence of the axial current in de Sitter spacetime.Comment: 28 pages, 5 figures. Includes minor changes clarifying the
phenomenological implications of the result
Universal Gravitational Wave Signatures of Cosmological Solitons
Cosmological solitonic objects such as monopoles, cosmic strings, domain
walls, oscillons and Q-balls often appear in theories of the early Universe. We
demonstrate that such scenarios are generically accompanied by a novel
production source of gravitational waves stemming from soliton isocurvature
perturbations. The resulting induced universal gravitational waves (UGWs)
reside at lower frequencies compared to gravitational waves typically
associated with soliton formation. We show that UGWs from axion-like particle
(ALP) oscillons, originating from ALP misalignment, extend the frequency range
of produced gravitational waves by more than two orders of magnitude regardless
of the ALP mass and decay constant and can be observable in upcoming
gravitational wave experiments. UGWs open a new route for gravitational wave
signatures in broad classes of cosmological theories.Comment: 8 pages, 2 figure
Production and backreaction of massive fermions during axion inflation with non-Abelian gauge fields
We study the production and backreaction of massive vector-like fermions in
the background of a classical SU(2) gauge field during axion-driven inflation.
We demonstrate all ultraviolet divergences due to the interactions with the
fermions can be absorbed by renormalization of the axion wavefunction and the
gauge coupling. The effects of the fermion-axion interaction vanish in the
massless limit as required by symmetry. For very massive fermions, contact
interactions are induced between the axion, the gauge field and the
gravitational field. In this massive limit, we find the usual axion-gauge field
interactions are induced, however, in addition we observe the appearance of
axion self-interactions, as well as kinetic braiding of the axion with the
Einstein tensor. These new axion derivative interactions present intriguing
opportunities for model building and phenomenology.Comment: 45 pages, 3 figure