6,860 research outputs found
Variability of fundamental constants
If the fine structure constant is not really constant, is this due to a
variation of , , or ? It is argued that the only reasonable
conclusion is a variable speed of light.Comment: preliminary draft, comments welcom
Doubly Special Relativity with a minimum speed and the Uncertainty Principle
The present work aims to search for an implementation of a new symmetry in
the space-time by introducing the idea of an invariant minimum speed scale
(). Such a lowest limit , being unattainable by the particles, represents
a fundamental and preferred reference frame connected to a universal background
field (a vacuum energy) that breaks Lorentz symmetry. So there emerges a new
principle of symmetry in the space-time at the subatomic level for very low
energies close to the background frame (), providing a fundamental
understanding for the uncertainty principle, i.e., the uncertainty relations
should emerge from the space-time with an invariant minimum speed.Comment: 10 pages, 8 figures, Correlated paper in:
http://www.worldscientific.com/worldscinet/ijmpd?journalTabs=read. arXiv
admin note: substantial text overlap with arXiv:physics/0702095,
arXiv:0705.4315, arXiv:0709.1727, arXiv:0805.120
Alternative derivation of the relativistic contribution to perihelic precession
An alternative derivation of the first-order relativistic contribution to
perihelic precession is presented. Orbital motion in the Schwarzschild geometry
is considered in the Keplerian limit, and the orbit equation is derived for
approximately elliptical motion. The method of solution makes use of coordinate
transformations and the correspondence principle, rather than the standard
perturbative approach. The form of the resulting orbit equation is similar to
that derived from Newtonian mechanics and includes first-order corrections to
Kepler's orbits due to general relativity. The associated relativistic
contribution to perihelic precession agrees with established first-order
results. The reduced radius for the circular orbit is in agreement to
first-order with that calculated from the Schwarzschild effective potential.
The method of solution is understandable by undergraduate students.Comment: 12 pages, 2 figures. Accepted for publication in the American Journal
of Physic
The Maxwell Lagrangian in purely affine gravity
The purely affine Lagrangian for linear electrodynamics, that has the form of
the Maxwell Lagrangian in which the metric tensor is replaced by the
symmetrized Ricci tensor and the electromagnetic field tensor by the tensor of
homothetic curvature, is dynamically equivalent to the Einstein-Maxwell
equations in the metric-affine and metric formulation. We show that this
equivalence is related to the invariance of the Maxwell Lagrangian under
conformal transformations of the metric tensor. We also apply to a purely
affine Lagrangian the Legendre transformation with respect to the tensor of
homothetic curvature to show that the corresponding Legendre term and the new
Hamiltonian density are related to the Maxwell-Palatini Lagrangian for the
electromagnetic field. Therefore the purely affine picture, in addition to
generating the gravitational Lagrangian that is linear in the curvature,
justifies why the electromagnetic Lagrangian is quadratic in the
electromagnetic field.Comment: 9 pages; published versio
Analytic Formulas for the Orientation Dependence of Step Stiffness and Line Tension: Key Ingredients for Numerical Modeling
We present explicit analytic, twice-differentiable expressions for the
temperature-dependent anisotropic step line tension and step stiffness for the
two principal surfaces of face-centered-cubic crystals, the square {001} and
the hexagonal {111}. These expressions improve on simple expressions that are
valid only for low temperatures and away from singular orientations. They are
well suited for implementation into numerical methods such as finite-element
simulation of step evolution.Comment: 10 pages; reformatted with revtex (with typos corrected) from version
accepted by SIAM--Multiscale Modeling and Simulation on Nov. 21, 2006;
greatly expanded introduction, several minor fixes (mostly stylistic
Can Solar System observations tell us something about the cosmological constant?
In this note we show that the latest determinations of the residual Mercury's
perihelion advance, obtained by accounting for almost all known Newtonian and
post-Newtonian orbital effects, yields only very broad constraints on the
cosmological constant. Indeed, from \delta\dot\omega=-0.0036 + - 0.0050
arcseconds per century one gets -2 10^-34 km^-2 < Lambda < 4 10^-35 km^-2. The
currently accepted value for Lambda, obtained from many independent
cosmological and large-scale measurements, amounts to almost 10^-46 km^-2.Comment: Latex2e, 4 pages, 2 table, no figures, 11 references. Table 2 added,
typos in the units of Lambda correcte
Action Principle for the Generalized Harmonic Formulation of General Relativity
An action principle for the generalized harmonic formulation of general
relativity is presented. The action is a functional of the spacetime metric and
the gauge source vector. An action principle for the Z4 formulation of general
relativity has been proposed recently by Bona, Bona--Casas and Palenzuela
(BBP). The relationship between the generalized harmonic action and the BBP
action is discussed in detail.Comment: This version is contains more thorough presentations and discussions
of the key results. To be published in PRD. (8 pages, no figures
On the Trace-Free Einstein Equations as a Viable Alternative to General Relativity
The quantum field theoretic prediction for the vacuum energy density leads to
a value for the effective cosmological constant that is incorrect by between 60
to 120 orders of magnitude. We review an old proposal of replacing Einstein's
Field Equations by their trace-free part (the Trace-Free Einstein Equations),
together with an independent assumption of energy--momentum conservation by
matter fields. While this does not solve the fundamental issue of why the
cosmological constant has the value that is observed cosmologically, it is
indeed a viable theory that resolves the problem of the discrepancy between the
vacuum energy density and the observed value of the cosmological constant.
However, one has to check that, as well as preserving the standard cosmological
equations, this does not destroy other predictions, such as the junction
conditions that underlie the use of standard stellar models. We confirm that no
problems arise here: hence, the Trace-Free Einstein Equations are indeed viable
for cosmological and astrophysical applications.Comment: Substantial changes from v1 including added author, change of title
and emphasis of the paper although all original results of v1. remai
The mystery of the cosmic vacuum energy density and the accelerated expansion of the Universe
After a short history of the -term it is explained why the
(effective) cosmological constant is expected to obtain contributions from
short-distance-physics, corresponding to an energy scale of at least 100 GeV.
The actual tiny value of the cosmological constant in any natural scale of
units represents, therefore, one of the deepest mysteries of present day
fundamental physics. We also briefly discuss recent astronomical evidence for a
cosmologically significant vacuum energy density causing an accelerating
expansion of the universe. This arises mainly from the Hubble diagram of type
Ia supernovae and from the observed temperature fluctuations of the cosmic
microwave background radiation. If this should become an established fact, we
are also confronted with a disturbing {\it cosmic coincidence} problem.Comment: 12 pages, 2 figures, iopart macros include
The Effects of Next-Nearest-Neighbor Interactions on the Orientation Dependence of Step Stiffness: Reconciling Theory with Experiment for Cu(001)
Within the solid-on-solid (SOS) approximation, we carry out a calculation of
the orientational dependence of the step stiffness on a square lattice with
nearest and next-nearest neighbor interactions. At low temperature our result
reduces to a simple, transparent expression. The effect of the strongest trio
(three-site, non pairwise) interaction can easily be incorporated by modifying
the interpretation of the two pairwise energies. The work is motivated by a
calculation based on nearest neighbors that underestimates the stiffness by a
factor of 4 in directions away from close-packed directions, and a subsequent
estimate of the stiffness in the two high-symmetry directions alone that
suggested that inclusion of next-nearest-neighbor attractions could fully
explain the discrepancy. As in these earlier papers, the discussion focuses on
Cu(001).Comment: 8 pages, 3 figures, submitted to Phys. Rev.
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