2,623 research outputs found
Infrared lessons for ultraviolet gravity: the case of massive gravity and Born-Infeld
We generalize the ultraviolet sector of gravitation via a Born-Infeld action
using lessons from massive gravity. The theory contains all of the elementary
symmetric polynomials and is treated in the Palatini formalism. We show how the
connection can be solved algebraically to be the Levi-Civita connection of an
effective metric. The non-linearity of the algebraic equations yields several
branches, one of which always reduces to General Relativity at low curvatures.
We explore in detail a {\it minimal} version of the theory, for which we study
solutions in the presence of a perfect fluid with special attention to the
cosmological evolution. In vacuum we recover Ricci-flat solutions, but also an
additional physical solution corresponding to an Einstein space. The existence
of two physical branches remains for non-vacuum solutions and, in addition, the
branch that connects to the Einstein space in vacuum is not very sensitive to
the specific value of the energy density. For the branch that connects to the
General Relativity limit we generically find three behaviours for the Hubble
function depending on the equation of state of the fluid, namely: either there
is a maximum value for the energy density that connects continuously with
vacuum, or the energy density can be arbitrarily large but the Hubble function
saturates and remains constant at high energy densities, or the energy density
is unbounded and the Hubble function grows faster than in General Relativity.
The second case is particularly interesting because it could offer an
interesting inflationary epoch even in the presence of a dust component.
Finally, we discuss the possibility of avoiding certain types of singularities
within the minimal model.Comment: 31 pages, 3 figures (Journal version, references added
A method to measure vacuum birefringence at FCC-ee
It is well-known that the Heisenberg-Euler-Schwinger effective Lagrangian
predicts that a vacuum with a strong static electromagnetic field turns
birefringent. We propose a scheme that can be implemented at the planned
FCC-ee, to measure the nonlinear effect of vacuum birefringence in
electrodynamics arising from QED corrections. Our scheme employs a pulsed laser
to create Compton backscattered photons off a high energy electron beam, with
the FCC-ee as a particularly interesting example. These photons will pass
through a strong static magnetic field, which changes the state of polarization
of the radiation - an effect proportional to the photon energy. This change
will be measured by the use of an aligned single-crystal, where a large
difference in the pair production cross-sections can be achieved. In the
proposed experimental setup the birefringence effect gives rise to a difference
in the number of pairs created in the analyzing crystal, stemming from the fact
that the initial laser light has a varying state of polarization, achieved with
a rotating quarter wave plate. Evidence for the vacuum birefringent effect will
be seen as a distinct peak in the Fourier transform spectrum of the
pair-production rate signal. This tell-tale signal can be significantly above
background with only few hours of measurement, in particular at high energies.Comment: Presented by UIU at the International Symposium on "New Horizons in
Fundamental Physics: From Neutrons Nuclei via Superheavy Elements and
Supercritical Fields to Neutron Stars and Cosmic Rays," held to honor Walter
Greiner on his 80th birthday at Makutsi Safari Farm, South Africa, November
23-29, 201
Unitary equivalence between ordinary intelligent states and generalized intelligent states
Ordinary intelligent states (OIS) hold equality in the Heisenberg uncertainty
relation involving two noncommuting observables {A, B}, whereas generalized
intelligent states (GIS) do so in the more generalized uncertainty relation,
the Schrodinger-Robertson inequality. In general, OISs form a subset of GISs.
However, if there exists a unitary evolution U that transforms the operators
{A, B} to a new pair of operators in a rotation form, it is shown that an
arbitrary GIS can be generated by applying the rotation operator U to a certain
OIS. In this sense, the set of OISs is unitarily equivalent to the set of GISs.
It is the case, for example, with the su(2) and the su(1,1) algebra that have
been extensively studied particularly in quantum optics. When these algebras
are represented by two bosonic operators (nondegenerate case), or by a single
bosonic operator (degenerate case), the rotation, or pseudo-rotation, operator
U corresponds to phase shift, beam splitting, or parametric amplification,
depending on two observables {A, B}.Comment: published version, 4 page
Unitary equivalence between ordinary intelligent states and generalized intelligent states
Ordinary intelligent states (OIS) hold equality in the Heisenberg uncertainty
relation involving two noncommuting observables {A, B}, whereas generalized
intelligent states (GIS) do so in the more generalized uncertainty relation,
the Schrodinger-Robertson inequality. In general, OISs form a subset of GISs.
However, if there exists a unitary evolution U that transforms the operators
{A, B} to a new pair of operators in a rotation form, it is shown that an
arbitrary GIS can be generated by applying the rotation operator U to a certain
OIS. In this sense, the set of OISs is unitarily equivalent to the set of GISs.
It is the case, for example, with the su(2) and the su(1,1) algebra that have
been extensively studied particularly in quantum optics. When these algebras
are represented by two bosonic operators (nondegenerate case), or by a single
bosonic operator (degenerate case), the rotation, or pseudo-rotation, operator
U corresponds to phase shift, beam splitting, or parametric amplification,
depending on two observables {A, B}.Comment: published version, 4 page
Cascading dust inflation in Born-Infeld gravity
In the framework of Born-Infeld inspired gravity theories, which deviates
from General Relativity (GR) in the high curvature regime, we discuss the
viability of Cosmic Inflation without scalar fields. For energy densities
higher than the new mass scale of the theory, a gravitating dust component is
shown to generically induce an accelerated expansion of the Universe. Within
such a simple scenario, inflation gracefully exits when the GR regime is
recovered, but the Universe would remain matter dominated. In order to
implement a reheating era after inflation, we then consider inflation to be
driven by a mixture of unstable dust species decaying into radiation. Because
the speed of sound gravitates within the Born-Infeld model under consideration,
our scenario ends up being predictive on various open questions of the
inflationary paradigm. The total number of e-folds of acceleration is given by
the lifetime of the unstable dust components and is related to the duration of
reheating. As a result, inflation does not last much longer than the number of
e-folds of deceleration allowing a small spatial curvature and large scale
deviations to isotropy to be observable today. Energy densities are
self-regulated as inflation can only start for a total energy density less than
a threshold value, again related to the species' lifetime. Above this
threshold, the Universe may bounce thereby avoiding a singularity. Another
distinctive feature is that the accelerated expansion is of the
superinflationary kind, namely the first Hubble flow function is negative. We
show however that the tensor modes are never excited and the tensor-to-scalar
ratio is always vanishing, independently of the energy scale of inflation.Comment: 28 pages, 4 figure
Kinetic energy driven superconductivity, the origin of the Meissner effect, and the reductionist frontier
Is superconductivity associated with a lowering or an increase of the kinetic
energy of the charge carriers? Conventional BCS theory predicts that the
kinetic energy of carriers increases in the transition from the normal to the
superconducting state. However, substantial experimental evidence obtained in
recent years indicates that in at least some superconductors the opposite
occurs. Motivated in part by these experiments many novel mechanisms of
superconductivity have recently been proposed where the transition to
superconductivity is associated with a lowering of the kinetic energy of the
carriers. However none of these proposed unconventional mechanisms explores the
fundamental reason for kinetic energy lowering nor its wider implications. Here
I propose that kinetic energy lowering is at the root of the Meissner effect,
the most fundamental property of superconductors. The physics can be understood
at the level of a single electron atom: kinetic energy lowering and enhanced
diamagnetic susceptibility are intimately connected. According to the theory of
hole superconductivity, superconductors expel negative charge from their
interior driven by kinetic energy lowering and in the process expel any
magnetic field lines present in their interior. Associated with this we predict
the existence of a macroscopic electric field in the interior of
superconductors and the existence of macroscopic quantum zero-point motion in
the form of a spin current in the ground state of superconductors (spin
Meissner effect). In turn, the understanding of the role of kinetic energy
lowering in superconductivity suggests a new way to understand the fundamental
origin of kinetic energy lowering in quantum mechanics quite generally
Electron-hole asymmetry is the key to superconductivity
In a solid, transport of electricity can occur via negative electrons or via
positive holes. In the normal state of superconducting materials experiments
show that transport is usually dominated by
. Instead, in the superconducting state experiments show that the
supercurrent is always carried by .
These experimental facts indicate that electron-hole asymmetry plays a
fundamental role in superconductivity, as proposed by the theory of hole
superconductivity.Comment: Presented at the New3SC-4 meeting, San Diego, Jan. 16-21 2003; to be
published in Int. J. Mod. Phys.
Born-Infeld inspired modifications of gravity
General Relativity has shown an outstanding observational success in the
scales where it has been directly tested. However, modifications have been
intensively explored in the regimes where it seems either incomplete or signals
its own limit of validity. In particular, the breakdown of unitarity near the
Planck scale strongly suggests that General Relativity needs to be modified at
high energies and quantum gravity effects are expected to be important. This is
related to the existence of spacetime singularities when the solutions of
General Relativity are extrapolated to regimes where curvatures are large. In
this sense, Born-Infeld inspired modifications of gravity have shown an
extraordinary ability to regularise the gravitational dynamics, leading to
non-singular cosmologies and regular black hole spacetimes in a very robust
manner and without resorting to quantum gravity effects. This has boosted the
interest in these theories in applications to stellar structure, compact
objects, inflationary scenarios, cosmological singularities, and black hole and
wormhole physics, among others. We review the motivations, various
formulations, and main results achieved within these theories, including their
observational viability, and provide an overview of current open problems and
future research opportunities.Comment: 212 pages, Review under press at Physics Report
Symmetry Principle Preserving and Infinity Free Regularization and renormalization of quantum field theories and the mass gap
Through defining irreducible loop integrals (ILIs), a set of consistency
conditions for the regularized (quadratically and logarithmically) divergent
ILIs are obtained to maintain the generalized Ward identities of gauge
invariance in non-Abelian gauge theories. Overlapping UV divergences are
explicitly shown to be factorizable in the ILIs and be harmless via suitable
subtractions. A new regularization and renormalization method is presented in
the initial space-time dimension of the theory. The procedure respects
unitarity and causality. Of interest, the method leads to an infinity free
renormalization and meanwhile maintains the symmetry principles of the original
theory except the intrinsic mass scale caused conformal scaling symmetry
breaking and the anomaly induced symmetry breaking. Quantum field theories
(QFTs) regularized through the new method are well defined and governed by a
physically meaningful characteristic energy scale (CES) and a physically
interesting sliding energy scale (SES) which can run from to a dynamically generated mass gap or to in the
absence of mass gap and infrared (IR) problem. It is strongly indicated that
the conformal scaling symmetry and its breaking mechanism play an important
role for understanding the mass gap and quark confinement.Comment: 59 pages, Revtex, 4 figures, 1 table, Erratum added, published
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