4,614 research outputs found
Some Implications of the Cosmological Constant to Fundamental Physics
In the presence of a cosmological constant, ordinary Poincare' special
relativity is no longer valid and must be replaced by a de Sitter special
relativity, in which Minkowski space is replaced by a de Sitter spacetime. In
consequence, the ordinary notions of energy and momentum change, and will
satisfy a different kinematic relation. Such a theory is a different kind of a
doubly special relativity. Since the only difference between the Poincare' and
the de Sitter groups is the replacement of translations by certain linear
combinations of translations and proper conformal transformations, the net
result of this change is ultimately the breakdown of ordinary translational
invariance. From the experimental point of view, therefore, a de Sitter special
relativity might be probed by looking for possible violations of translational
invariance. If we assume the existence of a connection between the energy scale
of an experiment and the local value of the cosmological constant, there would
be changes in the kinematics of massive particles which could hopefully be
detected in high-energy experiments. Furthermore, due to the presence of a
horizon, the usual causal structure of spacetime would be significantly
modified at the Planck scale.Comment: 15 pages, lecture presented at the "XIIth Brazilian School of
Cosmology and Gravitation", Mangaratiba, Rio de Janeiro, September 10-23,
200
Cosmological Term and Fundamental Physics
A nonvanishing cosmological term in Einstein's equations implies a
nonvanishing spacetime curvature even in absence of any kind of matter. It
would, in consequence, affect many of the underlying kinematic tenets of
physical theory. The usual commutative spacetime translations of the Poincare'
group would be replaced by the mixed conformal translations of the de Sitter
group, leading to obvious alterations in elementary concepts such as time,
energy and momentum. Although negligible at small scales, such modifications
may come to have important consequences both in the large and for the
inflationary picture of the early Universe. A qualitative discussion is
presented which suggests deep changes in Hamiltonian, Quantum and Statistical
Mechanics. In the primeval universe as described by the standard cosmological
model, in particular, the equations of state of the matter sources could be
quite different from those usually introduced.Comment: RevTeX, 4 pages. Selected for Honorable Mention in the Annual Essay
Competition of the Gravity Research Foundation for the year 200
On the 4D generalized Proca action for an Abelian vector field
We summarize previous results on the most general Proca theory in 4
dimensions containing only first-order derivatives in the vector field
(second-order at most in the associated St\"uckelberg scalar) and having only
three propagating degrees of freedom with dynamics controlled by second-order
equations of motion. Discussing the Hessian condition used in previous works,
we conjecture that, as in the scalar galileon case, the most complete action
contains only a finite number of terms with second-order derivatives of the
St\"uckelberg field describing the longitudinal mode, which is in agreement
with the results of JCAP 1405, 015 (2014) and Phys. Lett. B 757, 405 (2016) and
complements those of JCAP 1602, 004 (2016). We also correct and complete the
parity violating sector, obtaining an extra term on top of the arbitrary
function of the field , the Faraday tensor and its Hodge
dual .Comment: LaTeX file in jcappub style, 11 pages, no figures. v2: Minor changes
according to the referee requirements. A new parity-violating term in the
Lagrangian has been uncovered and the text has been changed accordingly. The
conclusions are, essentially, unchanged. v3: Miscellaneous changes. Version
to be published in Journal of Cosmology and Astroparticle Physic
On the stability and causality of scalar-vector theories
Various extensions of standard inflationary models have been proposed
recently by adding vector fields. Because they are generally motivated by
large-scale anomalies, and the possibility of statistical anisotropy of
primordial fluctuations, such models require to introduce non-standard
couplings between vector fields on the one hand, and either gravity or scalar
fields on the other hand. In this article, we study models involving a vector
field coupled to a scalar field. We derive restrictive necessary conditions for
these models to be both stable (Hamiltonian bounded by below) and causal
(hyperbolic equations of motion).Comment: 20 pages, references added, v2 matches published version in JCA
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