11 research outputs found
Hartree approximation in curved spacetimes revisited II: The semiclassical Einstein equations and de Sitter self-consistent solutions
We consider the semiclassical Einstein equations (SEE) in the presence of a
quantum scalar field with self-interaction . Working in the
Hartree truncation of the two-particle irreducible (2PI) effective action, we
compute the vacuum expectation value of the energy-momentum tensor of the
scalar field, which act as a source of the SEE. We obtain the renormalized SEE
by implementing a consistent renormalization procedure. We apply our results to
find self-consistent de Sitter solutions to the SEE in situations with or
without spontaneous breaking of the -symmetry.Comment: 32 pages, 4 figure
Quantum backreaction of -symmetric scalar fields and de Sitter spacetimes at the renormalization point: renormalization schemes and the screening of the cosmological constant
We consider a theory of self-interacting quantum scalar fields with
quartic -symmetric potential, with a coupling constant , in a
generic curved spacetime. We analyze the renormalization process of the
Semiclassical Einstein Equations at leading order in the expansion for
different renormailzation schemes, namely: the traditional one that sets the
geometry of the spacetime to be Minkowski at the renormalization point, and new
schemes (originally proposed in [1,2]) which set the geometry to be that of a
fixed de Sitter spacetime. In particular, we study the quantum backreaction for
fields in de Sitter spacetimes with masses much smaller than the expansion rate
. We find that the scheme that uses the classical de Sitter background
solution at the renormalization point, stands out as the most appropriate to
study the quantum effects on de Sitter spacetimes. Adopting such scheme we
obtain the backreaction is suppressed by with no logarithmic
enhancement factor of , giving only a small screening of the
classical cosmological constant due to the backreaction of such quantum fields.
We point out the use of the new schemes can also be more appropriate than the
traditional one to study quantum effects in other spacetimes relevant for
cosmology.Comment: 14 pages, 3 figures; v2 agrees with the published version; in v2 we
introduced new clarifications and we replaced the figures by new ones in
order to fix a mistake in v1 and to provide additional details of the result
The consistency condition for the three-point function in dissipative single-clock inflation
We generalize the consistency condition for the three-point function in
single field inflation to the case of dissipative, multi-field, single-clock
models. We use the recently introduced extension of the effective field theory
of inflation that accounts for dissipative effects, to provide an explicit
proof to leading (non-trivial) order in the generalized slow roll parameters
and mixing with gravity scales. Our results illustrate the conditions necessary
for the validity of the consistency relation in situations with many degrees of
freedom relevant during inflation, namely that there is a preferred clock.
Departures from this condition in forthcoming experiments would rule out not
only single field but also a large class of multi-field models.Comment: 26+11 page
Hartree approximation in curved spacetimes revisited: The effective potential in de Sitter spacetime
Constraints on conformal ultralight dark matter couplings from the European Pulsar Timing Array
International audienceMillisecond pulsars are extremely precise celestial clocks: as they rotate, the beamed radio waves emitted along the axis of their magnetic field can be detected with radio telescopes, which allows for tracking subtle changes in the pulsars' rotation periods. A possible effect on the period of a pulsar is given by a potential coupling to dark matter, in cases where it is modeled with an "ultralight" scalar field. In this paper, we consider a universal conformal coupling of the dark matter scalar to gravity, which in turn mediates an effective coupling between pulsars and dark matter. If the dark matter scalar field is changing in time, as expected in the Milky Way, this effective coupling produces a periodic modulation of the pulsar rotational frequency. By studying the time series of observed radio pulses collected by the European Pulsar Timing Array experiment, we present constraints on the coupling of dark matter, improving on existing bounds. These bounds can also be regarded as constraints on the parameters of scalar-tensor theories of the Fierz-Jordan-Brans-Dicke and Damour-Esposito-Farèse types in the presence of a (light) mass potential term
Constraints on conformal ultralight dark matter couplings from the European Pulsar Timing Array
International audienceMillisecond pulsars are extremely precise celestial clocks: as they rotate, the beamed radio waves emitted along the axis of their magnetic field can be detected with radio telescopes, which allows for tracking subtle changes in the pulsars' rotation periods. A possible effect on the period of a pulsar is given by a potential coupling to dark matter, in cases where it is modeled with an "ultralight" scalar field. In this paper, we consider a universal conformal coupling of the dark matter scalar to gravity, which in turn mediates an effective coupling between pulsars and dark matter. If the dark matter scalar field is changing in time, as expected in the Milky Way, this effective coupling produces a periodic modulation of the pulsar rotational frequency. By studying the time series of observed radio pulses collected by the European Pulsar Timing Array experiment, we present constraints on the coupling of dark matter, improving on existing bounds. These bounds can also be regarded as constraints on the parameters of scalar-tensor theories of the Fierz-Jordan-Brans-Dicke and Damour-Esposito-Farèse types in the presence of a (light) mass potential term