315 research outputs found
Magnetic fields from inflation?
We consider the possibility of generation of the seeds of primordial magnetic
field on inflation and show that the effect of the back reaction of this field
can be very important. Assuming that back reaction does not spoil inflation we
find a rather strong restriction on the amplitude of the primordial seeds which
could be generated on inflation. Namely, this amplitude recalculated to the
present epoch cannot exceed in scales. This field seems to be
too small to be amplified to the observable values by galactic dynamo
mechanism.Comment: 10 page
New nonlocal effective action
We suggest a new method for the calculation of the nonlocal part of the
effective action. It is based on resummation of perturbation series for the
heat kernel and its functional trace at large values of the proper time
parameter. We derive a new, essentially nonperturbative, nonlocal contribution
to the effective action in spacetimes with dimensions .Comment: 28 pages, latex, no figures, typos are corrected, presentation
improve
On Pairs of Difference Operators Satisfying: [P,Q] = Id
Different finite difference replacements for the derivative are analyzed in
the context of the Heisenberg commutation relation. The type of the finite
difference operator is shown to be tied to whether one can naturally consider
and to be self-adjoint and skew self-adjoint or whether they have to be
viewed as creation and annihilation operators. The first class, generalizing
the central difference scheme, is shown to give unitary equivalent
representations. For the second case we construct a large class of examples,
generalizing previously known difference operator realizations of .Comment: 32 pages, plain Te
Charged Scalar Self-Mass during Inflation
We compute the one loop self-mass of a charged massless, minimally coupled
scalar in a locally de Sitter background geometry. The computation is done in
two different gauges: the noninvariant generalization of Feynman gauge which
gives the simplest expression for the photon propagator and the de Sitter
invariant gauge of Allen and Jacobson. In each case dimensional regularization
is employed and fully renormalized results are obtained. By using our result in
the linearized, effective field equations one can infer how the scalar responds
to the dielectric medium produced by inflationary particle production. We also
work out the result for a conformally coupled scalar. Although the conformally
coupled case is of no great physical interest the fact that we obtain a
manifestly de Sitter invariant form for its self-mass-squared establishes that
our noninvariant gauge introduces no physical breaking of de Sitter invariance
at one loop order.Comment: 41 pages, LaTeX 2epsilon, 3 figures, uses axodra
Inflationary Hubble Parameter from the Gravitational Wave Spectrum in the General Slow-roll Approximation
Improved general slow-roll formulae giving the primordial gravitational wave
spectrum are derived in the present work. Also the first and second order
general slow-roll inverse formulae giving the Hubble parameter in terms of
the gravitational wave spectrum are derived. Moreover, the general slow-roll
consistency condition relating the scalar and tensor spectra is obtained
Hardness of materials at high temperature and high pressure
International audienceIntrinsic character of correlation between hardness and thermodynamic properties of solids has been established. The proposed thermodynamic model of hardness allows one to easily estimate hardness and bulk moduli of known or even hypothetical solids from the data on Gibbs energy of atomization of the elements or on the enthalpy at the melting point. The correctness of this approach has been illustrated by an example of the recently synthesized superhard diamond-like BC5 and orthorhombic modification of boron, γ-B28. The pressure and/or temperature dependences of hardness have been calculated for a number of hard and superhard phases, i.e. diamond, cBN, B6O, B4C, SiC, Al2O3, β-B2O3 and β-rh boron. The excellent agreement between experimental and calculated values has been observed for temperature dependences of Vickers and Knoop hardness. Besides, the model predicts that some materials can become harder than diamond already at pressures in the megabar range.
Friedmann Equations from Entropic Force
In this note by use of the holographic principle together with the
equipartition law of energy and the Unruh temperature, we derive the Friedmann
equations of a Friedmann-Robertson-Walker universe.Comment: latex, 8 pages, v2: minor modifications and to appear in PRD (Rapid
Communication
Breaking scale invariance from a singular inflaton potential
In this paper we break the scale invariance of the primordial power spectrum
of curvature perturbations of inflation. Introducing a singular behaviour due
to spontaneous symmetry breaking in the inflaton potential, we obtain fully
analytic expressions of scale dependent oscillation and a modulation in power
on small scale in the primordial spectrum. And we give the associated cosmic
microwave background and matter power spectra which we can observe now and
discuss the signature of the scale dependence. We also address the possibility
of whether some inflationary model with featured potential might mimic the
predictions of the scale invariant power spectrum. We present some examples
which illustrate such degeneracies.Comment: 20 pages, 9 figures; Discussion expanded and references added;
Miscellaneous typos correcte
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