1,076 research outputs found
On the issue of imposing boundary conditions on quantum fields
An interesting example of the deep interrelation between Physics and
Mathematics is obtained when trying to impose mathematical boundary conditions
on physical quantum fields. This procedure has recently been re-examined with
care. Comments on that and previous analysis are here provided, together with
considerations on the results of the purely mathematical zeta-function method,
in an attempt at clarifying the issue. Hadamard regularization is invoked in
order to fill the gap between the infinities appearing in the QFT renormalized
results and the finite values obtained in the literature with other procedures.Comment: 13 pages, no figure
Zeta-function regularization, the multiplicative anomaly and the Wodzicki residue
The multiplicative anomaly associated with the zeta-function regularized
determinant is computed for the Laplace-type operators L_1=-\lap+V_1 and
L_2=-\lap+V_2, with , constant, in a D-dimensional compact smooth
manifold , making use of several results due to Wodzicki and by direct
calculations in some explicit examples. It is found that the multiplicative
anomaly is vanishing for odd and for D=2. An application to the one-loop
effective potential of the O(2) self-interacting scalar model is outlined.Comment: LaTeX, 17 pages, 3 figures. Small corrections, two new formulas, and
an addition to the references. To appear in Commun. Math. Phy
Zeta-Function Regularization is Uniquely Defined and Well
Hawking's zeta function regularization procedure is shown to be rigorously
and uniquely defined, thus putting and end to the spreading lore about
different difficulties associated with it. Basic misconceptions,
misunderstandings and errors which keep appearing in important scientific
journals when dealing with this beautiful regularization method ---and other
analytical procedures--- are clarified and corrected.Comment: 7 pages, LaTeX fil
Dark energy in modified Gauss-Bonnet gravity: late-time acceleration and the hierarchy problem
Dark energy cosmology is considered in a modified Gauss-Bonnet (GB) model of
gravity where an arbitrary function of the GB invariant, , is added to
the General Relativity action. We show that such theory is endowed with a quite
rich cosmological structure: it may naturally lead to an effective cosmological
constant, quintessence or phantom cosmic acceleration, with a possible
transition from deceleration to acceleration. It is demonstrated in the paper
that this theory is perfectly viable, since it is compliant with Solar System
constraints. Specific properties of gravity in a de Sitter universe,
such as dS and SdS solutions, their entropy and its explicit one-loop
quantization are studied. The issue of a possible solution of the hierarchy
problem in modified gravities is addressed too.Comment: LaTeX file 20 pages, new subsections are adde
Beyond-one-loop quantum gravity action yielding both inflation and late-time acceleration
A unified description of early-time inflation with the current cosmic
acceleration is achieved by means of a new theory that uses a quadratic model
of gravity, with the inclusion of an exponential -gravity contribution
for dark energy. High-curvature corrections of the theory come from
higher-derivative quantum gravity and yield an effective action that goes
beyond the one-loop approximation. It is shown that, in this theory, viable
inflation emerges in a natural way, leading to a spectral index and
tensor-to-scalar ratio that are in perfect agreement with the most reliable
Planck results. At low energy, late-time accelerated expansion takes place. As
exponential gravity, for dark energy, must be stabilized during the matter and
radiation eras, we introduce a curing term in order to avoid nonphysical
singularities in the effective equation of state parameter. The results of our
analysis are confirmed by accurate numerical simulations, which show that our
model does fit the most recent cosmological data for dark energy very
precisely.Comment: 20 pages, to appear in NP
Black hole and de Sitter solutions in a covariant renormalizable field theory of gravity
It is shown that Schwarzschild black hole and de Sitter solutions exist as
exact solutions of a recently proposed relativistic covariant formulation of
(power-counting) renormalizable gravity with a fluid. The formulation without a
fluid is also presented here. The stability of the solutions is studied and
their corresponding entropies are computed, by using the covariant Wald method.
The area law is shown to hold both for the Schwarzschild and for the de Sitter
solutions found, confirming that, for the case, one is dealing with a
minimal modification of GR.Comment: 7 paages, latex fil
String-inspired Gauss-Bonnet gravity reconstructed from the universe expansion history and yielding the transition from matter dominance to dark energy
We consider scalar-Gauss-Bonnet and modified Gauss-Bonnet gravities and
reconstruct these theories from the universe expansion history. In particular,
we are able to construct versions of those theories (with and without ordinary
matter), in which the matter dominated era makes a transition to the cosmic
acceleration epoch. It is remarkable that, in several of the cases under
consideration, matter dominance and the deceleration-acceleration transition
occur in the presence of matter only. The late-time acceleration epoch is
described asymptotically by de Sitter space but may also correspond to an exact
CDM cosmology, having in both cases an effective equation of state
parameter close to -1. The one-loop effective action of modified
Gauss-Bonnet gravity on the de Sitter background is evaluated and it is used to
derive stability criteria for the ensuing de Sitter universe.Comment: LaTeX20 pages, 4 figures, version to apear in PR
On structure of effective action in four-dimensional quantum dilaton supergravity
A general structure of effective action in new chiral superfield model
associated with , supergravity is investigated. This model
corresponds to finite quantum field theory and does not demand the
regularization and renormalization at effective action calculation. It is shown
that in local approximation the effective action is defined by two objects
called general superfield effective lagrangian and chiral superfield effective
lagrangian. A proper-time method is generalized for calculation of these two
effective lagrangians in superfield manner. Power expansion of the effective
action in supercovariant derivatives is formulated and the lower terms of such
an expansion are calculated in explicit superfield form
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