315 research outputs found
The Eternal Sunshine of the Spotless Mind
We extend the worldline measure for pocket formation in eternal inflation to
allow for time-ordered bubble formation. Such a time-ordering is equivalent to
imposing a preferred time-slicing on the "parent" de Sitter space. Using this
measure, we describe a covariant version of the youngness paradox and show that
the youngness paradox is a gauge artifact if the parent spacetime is an
unbroken de Sitter space, due to the lack of an explicit time-ordering for the
bubble nucleation events. We then show that one can add a "clock" to the de
Sitter space, in the form of a vector field with a spontaneously broken
symmetry that defines a unique timelike direction accessible to all observers.
Once this is done, the existence of a preferred slicing means that the
youngness paradox cannot be easily resolved. We use this to elucidate the
apparent "persistence of memory" discussed recently by Garriga, Guth and
Vilenkin, for inflationary universes produced by bubble nucleation.Comment: 18 pages, 5 figure
Haloes of k-Essence
We study gravitationally bound static and spherically symmetric
configurations of k-essence fields. In particular, we investigate whether these
configurations can reproduce the properties of dark matter haloes. The classes
of Lagrangians we consider lead to non-isotropic fluids with barotropic and
polytropic equations of state. The latter include microscopic realizations of
the often-considered Chaplygin gases, which we find can cluster into dark
matter halo-like objects with flat rotation curves, while exhibiting a dark
energy-like negative pressure on cosmological scales. We complement our studies
with a series of formal general results about the stability and initial value
formulation of non-canonical scalar field theories, and we also discuss a new
class of de Sitter solutions with spacelike field gradients.Comment: 34pages, single column double spacing, 7 figures, 3 Tables, RevTex4.
Additional references and minor clarifications. To be submitted to JCA
Formulating Weak Lensing from the Boltzmann Equation and Application to Lens-lens Couplings
The Planck mission has conclusively detected lensing of the Cosmic Microwave
Background (CMB) radiation from foreground sources to an overall significance
of greater than . The high precision of this measurement motivates
the development of a more complete formulation of the calculation of this
effect. While most effects on the CMB anisotropies are widely studied through
direct solutions of the Boltzmann equation, the non-linear effect of CMB
lensing is formulated through the solutions of the geodesic equation. In this
paper, we present a new formalism to the calculation of the lensing effect by
\emph{directly solving the Boltzmann equation}, as we did in the calculation of
the CMB anisotropies at recombination. In particular, we developed a
diagrammatic approach to efficiently keep track of all the interaction terms
and calculate all possible non-trivial correlations to arbitrary high orders.
Using this formalism, we explicitly articulate the approximations required to
recover the usual remapping approach used in current studies of the weak
lensing. In addition, we point out additional unexplored corrections that are
manifest in our formalism to which experiments may be sensitive. As an example,
we calculate the correction to the CMB temperature power spectrum for the
\emph{lens-lens} coupling effects which are neglected in standard calculations.
We find that the correction is of the CMB temperature power
spectrum for up to 3000 and thus is comparable to the cosmic variance.Comment: 25 pages, 3 figures, 4 tables, CMB, lensin
Lorentz-Violating Vector Fields Slow the Universe Down
We consider the gravitational effects of a single, fixed-norm,
Lorentz-violating timelike vector field. In a cosmological background, such a
vector field acts to rescale the effective value of Newton's constant. The
energy density of this vector field precisely tracks the energy density of the
rest of the universe, but with the opposite sign, so that the universe
experiences a slower rate of expansion for a given matter content. This vector
field similarly rescales Newton's constant in the Newtonian limit, although by
a different factor. We put constraints on the parameters of the theory using
the predictions of primordial nucleosynthesis, demonstrating that the norm of
the vector field should be less than the Planck scale by an order of magnitude
or more.Comment: 15 pages, Revtex4, updated version. Added References. Minor Typos
corrected. Older version published in PR
Dust of Dark Energy
We introduce a novel class of field theories where energy always flows along
timelike geodesics, mimicking in that respect dust, yet which possess non-zero
pressure. This theory comprises two scalar fields, one of which is a Lagrange
multiplier enforcing a constraint between the other's field value and
derivative. We show that this system possesses no wave-like modes but retains a
single dynamical degree of freedom. Thus, the sound speed is always identically
zero on all backgrounds. In particular, cosmological perturbations reproduce
the standard behaviour for hydrodynamics with vanishing sound speed. Using all
these properties we propose a model unifying Dark Matter and Dark Energy in a
single degree of freedom. In a certain limit this model exactly reproduces the
evolution history of Lambda-CDM, while deviations away from the standard
expansion history produce a potentially measurable difference in the evolution
of structure.Comment: 13 pages, 3 figures. Added references, corrected language
A scattering theory of ultrarelativistic solitons
We construct a perturbative framework for understanding the collision of
solitons (more precisely, solitary waves) in relativistic scalar field
theories. Our perturbative framework is based on the suppression of the
space-time interaction area proportional to , where is the
relative velocity of an incoming solitary wave and . We calculate the leading order results for collisions of (1+1) dimensional
kinks in periodic potentials, and provide explicit, closed form expressions for
the phase shift and the velocity change after the collisions. We find excellent
agreement between our results and detailed numerical simulations. Crucially,
our perturbation series is controlled by a kinematic parameter, and hence not
restricted to small deviations around integrable cases such as the Sine-Gordon
model.Comment: v3: 43 pages, 10 figures, references added, matches version accepted
for publication in PR
The Quantum Information of Cosmological Correlations
It has been shown that the primordial perturbations sourced by inflation are
driven to classicality by unitary evolution alone. However, their coupling with
the environment such as photons and subsequent decoherence renders the
cosmological correlations quantum, losing primordial information in the
process. We argue that the quantumness of the resulting cosmological
correlations is given by quantum discord, which captures non-classical behavior
beyond quantum entanglement. By considering the environment as a quantum
channel in which primordial information contained in the perturbations is
transmitted to us, we can then ask how much of this information is
inaccessible. We show that this amount of information is given by the discord
of the joint primordial perturbations-environment system. To illustrate these
points, we model the joint system as a mixed bi-modal Gaussian state, and show
that quantum discord is dependent on the basis which decoherence occurs.Comment: 9 pages. 2 figure
3-pt Statistics of Cosmological Stochastic Gravitational Waves
We consider the 3-pt function (i.e. the bispectrum or non-Gaussianity) for
stochastic backgrounds of gravitational waves. We estimate the amplitude of
this signal for the primordial inflationary background, gravitational waves
generated during preheating, and for gravitational waves produced by
self-ordering scalar fields following a global phase transition. To assess
detectability, we describe how to extract the 3-pt signal from an idealized
interferometric experiment and compute the signal to noise ratio as a function
of integration time. The 3-pt signal for the stochastic gravitational wave
background generated by inflation is unsurprisingly tiny. For gravitational
radiation generated by purely causal, classical mechanisms we find that, no
matter how non-linear the process is, the 3-pt correlations produced vanish in
direct detection experiments. On the other hand, we show that in scenarios
where the B-mode of the CMB is sourced by gravitational waves generated by a
global phase transition, a strong 3-pt signal among the polarization modes
could also be produced. This may provide another method of distinguishing
inflationary B-modes. To carry out this computation, we have developed a
diagrammatic approach to the calculation of stochastic gravitational waves
sourced by scalar fluids, which has applications beyond the present scenario.Comment: 16 pages, 5 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
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