163 research outputs found
Spinorial Field and Lyra Geometry
The Dirac field is studied in a Lyra space-time background by means of the
classical Schwinger Variational Principle. We obtain the equations of motion,
establish the conservation laws, and get a scale relation relating the
energy-momentum and spin tensors. Such scale relation is an intrinsic property
for matter fields in Lyra background.Comment: 10 pages. Some misprints correcte
Bulk viscosity driving the acceleration of the Universe
The possibility that the present acceleration of the universe is driven by a
kind of viscous fluid is exploited. At background level this model is similar
to the generalized Chaplygin gas model (GCGM). But, at perturbative level, the
viscous fluid exhibits interesting properties. In particular the oscillations
in the power spectrum that plagues the GCGM are not present. Possible
fundamental descriptions for this viscous dark energy are discussed.Comment: Latex file, 8 pages, 3 eps figure
The δN formula is the dynamical renormalization group
We derive the 'separate universe' method for the inflationary bispectrum,
beginning directly from a field-theory calculation. We work to tree-level in
quantum effects but to all orders in the slow-roll expansion, with masses
accommodated perturbatively. Our method provides a systematic basis to account
for novel sources of time-dependence in inflationary correlation functions, and
has immediate applications. First, we use our result to obtain the correct
matching prescription between the 'quantum' and 'classical' parts of the
separate universe computation. Second, we elaborate on the application of this
method in situations where its validity is not clear. As a by-product of our
calculation we give the leading slow-roll corrections to the three-point
function of field fluctuations on spatially flat hypersurfaces in a canonical,
multiple-field model.Comment: v1: 33 pages, plus appendix and references; 5 figures. v2:
typographical typos fixed, minor changes to the main text and abstract,
reference added; matches version published in JCA
Issues Concerning Loop Corrections to the Primordial Power Spectra
We expound ten principles in an attempt to clarify the debate over infrared
loop corrections to the primordial scalar and tensor power spectra from
inflation. Among other things we note that existing proposals for nonlinear
extensions of the scalar fluctuation field introduce new ultraviolet
divergences which no one understands how to renormalize. Loop corrections and
higher correlators of these putative observables would also be enhanced by
inverse powers of the slow roll parameter . We propose an extension
which should be better behaved.Comment: 36 pages, uses LaTeX2e, version 3 revised for publication with a much
expanded section 4, proving that our proposed extension of the zeta-zeta
correlator absorbs the one loop infrared divergences from graviton
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