47 research outputs found
The Hubble Slow Roll Expansion for Multi Field Inflation
We examine the dynamics of inflation driven by multiple, interacting scalar
fields and derive a multi field version of the Hubble slow roll expansion. We
show that the properties of this expansion naturally generalize those of the
single field case. We present an analogous hierarchy of slow roll parameters,
and derive the system of ``flow'' equations that describes their evolution, and
show that when this system is truncated at finite order, it can always be
solved exactly. Lastly, we express the scalar and tensor perturbation spectra
in terms of the slow roll parameters
On the Suppression of Parametric Resonance and the Viability of Tachyonic Preheating after Multi-Field Inflation
We investigate the feasibility of explosive particle production via
parametric resonance or tachyonic preheating in multi-field inflationary models
by means of lattice simulations. We observe a strong suppression of resonances
in the presence of four-leg interactions between the inflaton fields and a
scalar matter field, leading to insufficient preheating when more than two
inflatons couple to the same matter field. This suppression is caused by a
dephasing of the inflatons that increases the effective mass of the matter
field.
Including three-leg interactions leads to tachyonic preheating, which is not
suppressed by an increase in the number of fields. If four-leg interactions are
sub-dominant, we observe a slight enhancement of tachyonic preheating. Thus, in
order for preheating after multi-field inflation to be efficient, one needs to
ensure that three-leg interactions are present. If no tachyonic contributions
exist, we expect the old theory of reheating to be applicable.Comment: v2: reference added, identical with PRD version, 23 pages, 3 figure
Gravitational Wave Production At The End Of Inflation
We consider gravitational wave production due to parametric resonance at the
end of inflation, or ``preheating''. This leads to large inhomogeneities which
source a stochastic background of gravitational waves at scales inside the
comoving Hubble horizon at the end of inflation. We confirm that the present
amplitude of these gravitational waves need not depend on the inflationary
energy scale. We analyze an explicit model where the inflationary energy scale
is ~10^9 GeV, yielding a signal close to the sensitivity of Advanced LIGO and
BBO. This signal highlights the possibility of a new observational ``window''
into inflationary physics, and provides significant motivation for searches for
stochastic backgrounds of gravitational waves in the Hz to GHz range, with an
amplitude on the order of \Omega_{gw}(k)h^2 ~ 10^-11. Finally, the strategy
used in our numerical computations is applicable to the gravitational waves
generated by many inhomogeneous processes in the early universe.Comment: 4 pages, Revtex, 2 figures. v2 References added, discussion clarified
and improved. v3 further clarification, typo regarding source corrected.
Basic results unchange