34 research outputs found
New counterterms induced by trans-Planckian physics in semiclassical gravity
We consider free and self-interacting quantum scalar fields satisfying
modified dispersion relations in the framework of Einstein-Aether theory. Using
adiabatic regularization, we study the renormalization of the equation for the
mean value of the field in the self-interacting case, and the renormalization
of the semiclassical Einstein-Aether equations for free fields. In both cases
we consider Bianchi type I background spacetimes. Contrary to what happens for
{\it free} fields in {\it flat} Robertson-Walker spacetimes, the
self-interaction and/or the anisotropy produce non-purely geometric terms in
the adiabatic expansion, i.e terms that involve both the metric
and the aether field . We argue that, in a general spacetime, the
renormalization of the theory would involve new counterterms constructed with
and , generating a fine-tuning problem for the
Einstein-Aether theory
Backreaction in trans-Planckian cosmology: renormalization, trace anomaly and selfconsistent solutions
We analyze the semiclassical Einstein equations for quantum scalar fields
satisfying modified dispersion relations. We first discuss in detail the
renormalization procedure based on adiabatic subtraction and dimensional
regularization. We show that, contrary to what expected from power counting
arguments, in 3+1 dimensions the subtraction involves up to the fourth
adiabatic order even for dispersion relations containing higher powers of the
momentum. Then we analyze the dependence of the trace of the renormalized
energy momentum tensor with the scale of new physics, and we recover the usual
trace anomaly in the appropriate limit. We also find selfconsistent de Sitter
solutions for dispersion relations that contain up to the fourth power of the
momentum. Using this particular example, we also discuss the possibility that
the modified dispersion relation can be mimicked at lower energies by an
effective initial state in a theory with the usual dispersion relation.Comment: 19 pages, 3 figure
Adiabatic renormalization in theories with modified dispersion relations
We generalize the adiabatic renormalization to theories with dispersion
relations modified at energies higher than a new scale . We obtain
explicit expressions for the mean value of the stress tensor in the adiabatic
vacuum, up to the second adiabatic order. We show that for any dispersion
relation the divergences can be absorbed into the bare gravitational constants
of the theory. We also point out that, depending on the renormalization
prescription, the renormalized stress tensor may contain finite trans-Planckian
corrections even in the limit .Comment: Typos corrected; to appear in the Proceedings of IRGAC 06, Journal of
Physics
Neutron-induced defects in optical fibers
We present a study on 0.8 MeV neutron-induced defects up to fluences of 1017 n/cm² in fluorine doped opticalfibers by using electron paramagnetic resonance, optical absorption and confocal micro-luminescence techniques. Our results allow to address the microscopic mechanisms leading to the generation of Silica-related point-defects such as E’, H(I), POR and NBOH Center
Anomalous Dimensions and Non-Gaussianity
We analyze the signatures of inflationary models that are coupled to strongly
interacting field theories, a basic class of multifield models also motivated
by their role in providing dynamically small scales. Near the squeezed limit of
the bispectrum, we find a simple scaling behavior determined by operator
dimensions, which are constrained by the appropriate unitarity bounds.
Specifically, we analyze two simple and calculable classes of examples:
conformal field theories (CFTs), and large-N CFTs deformed by relevant
time-dependent double-trace operators. Together these two classes of examples
exhibit a wide range of scalings and shapes of the bispectrum, including nearly
equilateral, orthogonal and local non-Gaussianity in different regimes. Along
the way, we compare and contrast the shape and amplitude with previous results
on weakly coupled fields coupled to inflation. This signature provides a
precision test for strongly coupled sectors coupled to inflation via irrelevant
operators suppressed by a high mass scale up to 1000 times the inflationary
Hubble scale.Comment: 40 pages, 10 figure
Einstein-aether as a quantum effective field theory
The possibility that Lorentz symmetry is violated in gravitational processes
is relatively unconstrained by experiment, in stark contrast with the level of
accuracy to which Lorentz symmetry has been confirmed in the matter sector. One
model of Lorentz violation in the gravitational sector is Einstein-aether
theory, in which Lorentz symmetry is broken by giving a vacuum expectation
value to a dynamical vector field. In this paper we analyse the effective
theory for quantised gravitational and aether perturbations. We show that this
theory possesses a controlled effective expansion within dimensional
regularisation, that is, for any process there are a finite number of Feynman
diagrams which will contribute to a given order of accuracy. We find that there
is no log-running of the two-derivative phenomenological parameters, justifying
the use of experimental constraints for these parameters obtained over many
orders of magnitude in energy scale. Given the stringent experimental bounds on
two-derivative Lorentz-violating operators, we estimate the size of matter
Lorentz-violation which arises due to loop effects. This amounts to an
estimation of the natural size of coefficients for Lorentz-violating
dimension-six matter operators, which in turn can be used to obtain a new bound
on the two-derivative parameters of this theory.Comment: 21 page
EFT beyond the horizon: stochastic inflation and how primordial quantum fluctuations go classical
We identify the effective theory describing inflationary super-Hubble scales and show it to be a special case of effective field theories appropriate to open systems. Open systems allow information to be exchanged between the degrees of freedom of interest and those that are integrated out, such as for particles moving through a fluid. Strictly speaking they cannot in general be described by an effective lagrangian; rather the appropriate `low-energy' limit is instead a Lindblad equation describing the evolution of the density matrix of the slow degrees of freedom. We derive the equation relevant to super-Hubble modes of quantum fields in near-de Sitter spacetimes and derive two implications. We show the evolution of the diagonal density-matrix elements quickly approaches the Fokker-Planck equation of Starobinsky's stochastic inflationary picture. This provides an alternative first-principles derivation of this picture's stochastic noise and drift, as well as its leading corrections. (An application computes the noise for systems with a sub-luminal sound speed.) We argue that the presence of interactions drives the off-diagonal density-matrix elements to zero in the field basis. This shows why the field basis is the `pointer basis' for the decoherence of primordial quantum fluctuations while they are outside the horizon, thus allowing them to re-enter as classical fluctuations, as assumed when analyzing CMB data. The decoherence process is efficient, occurring after several Hubble times even for interactions as weak as gravitational-strength. Crucially, the details of the interactions largely control only the decoherence time and not the nature of the final late-time stochastic state, much as interactions can control the equilibration time for thermal systems but are largely irrelevant to the properties of the resulting equilibrium state