165 research outputs found
Lorentz Transformation from Symmetry of Reference Principle
The Lorentz Transformation is traditionally derived requiring the Principle
of Relativity and light-speed universality. While the latter can be relaxed,
the Principle of Relativity is seen as core to the transformation. The present
letter relaxes both statements to the weaker, Symmetry of Reference Principle.
Thus the resulting Lorentz transformation and its consequences (time
dilatation, length contraction) are, in turn, effects of how we manage space
and time.Comment: 2 page
Stochastic motion of test particle implies that G varies with time
The aim of this letter is to propose a new description to the time varying
gravitational constant problem, which naturally implements the Dirac's large
numbers hypothesis in a new proposed holographic scenario for the origin of
gravity as an entropic force. We survey the effect of the Stochastic motion of
the test particle in Verlinde's scenario for gravity\cite{Verlinde}. Firstly we
show that we must get the equipartition values for which
leads to the usual Newtonian gravitational constant. Secondly,the stochastic
(Brownian) essence of the motion of the test particle, modifies the Newton's
2'nd law. The direct result is that the Newtonian constant has been time
dependence in resemblance as \cite{Running}.Comment: Accepted in International Journal of Theoretical Physic
Refractive-index saturation-mediated multiple line emission in polymer thin-film distributed-feedback lasers.
We report experimental and theoretical investigations of multiple laser-line emission in a distributed-feedback dye laser pumped by two coherent optical beams. We have used a Lloyd interferometer configuration with second- and third-order Bragg reflections to study the interaction between the two incident pumps in an organic thin film. We demonstrated theoretically that the number of laser emission lines can be interpreted with reference to the saturation effect in the refractive index
A Chern-Simons approach to Galilean quantum gravity in 2+1 dimensions
We define and discuss classical and quantum gravity in 2+1 dimensions in the
Galilean limit. Although there are no Newtonian forces between massive objects
in (2+1)-dimensional gravity, the Galilean limit is not trivial. Depending on
the topology of spacetime there are typically finitely many topological degrees
of freedom as well as topological interactions of Aharonov-Bohm type between
massive objects. In order to capture these topological aspects we consider a
two-fold central extension of the Galilei group whose Lie algebra possesses an
invariant and non-degenerate inner product. Using this inner product we define
Galilean gravity as a Chern-Simons theory of the doubly-extended Galilei group.
The particular extension of the Galilei group we consider is the classical
double of a much studied group, the extended homogeneous Galilei group, which
is also often called Nappi-Witten group. We exhibit the Poisson-Lie structure
of the doubly extended Galilei group, and quantise the Chern-Simons theory
using a Hamiltonian approach. Many aspects of the quantum theory are determined
by the quantum double of the extended homogenous Galilei group, or Galilei
double for short. We study the representation theory of the Galilei double,
explain how associated braid group representations account for the topological
interactions in the theory, and briefly comment on an associated
non-commutative Galilean spacetime.Comment: 38 pages, 1 figure, references update
Squashed Giants: Bound States of Giant Gravitons
We consider giant gravitons in the maximally supersymmetric type IIB
plane-wave, in the presence of a constant NSNS B-field background. We show that
in response to the background B-field the giant graviton would take the shape
of a deformed three-sphere, the size and shape of which depend on the B-field,
and that the giant becomes classically unstable once the B-field is larger than
a critical value B_{cr}. In particular, for the B-field which is
(anti-)self-dual under the SO(4) isometry of the original giant S^3, the closed
string metric is that of a round S^3, while the open string metric is a
squashed three-sphere. The squashed giant can be interpreted as a bound state
of a spherical three-brane and circular D-strings. We work out the spectrum of
geometric fluctuations of the squashed giant and study its stability. We also
comment on the gauge theory which lives on the brane (which is generically a
noncommutative theory) and a possible dual gauge theory description of the
deformed giant.Comment: Latex file, 32 pages, 6 .eps figures; v3: typos correcte
SD-brane gravity fields and rolling tachyons
S(pacelike)D-branes are objects arising naturally in string theory when
Dirichlet boundary conditions are imposed on the time direction. SD-brane
physics is inherently time-dependent. Previous investigations of gravity fields
of SD-branes have yielded undesirable naked spacelike singularities. We set up
the problem of coupling the most relevant open-string tachyonic mode to
massless closed-string modes in the bulk, with backreaction and Ramond-Ramond
fields included. We find solutions numerically in a self-consistent
approximation; our solutions are naturally asymptotically flat and
time-reversal asymmetric. We find completely nonsingular evolution; in
particular, the dilaton and curvature are well-behaved for all time. The
essential mechanism for spacetime singularity resolution is the inclusion of
full backreaction between the bulk fields and the rolling tachyon. Our analysis
is not the final word on the story, because we have to make some significant
approximations, most notably homogeneity of the tachyon on the unstable branes.
Nonetheless, we provide significant progress in plugging a gaping hole in prior
understanding of the gravity fields of SD-branes.Comment: References added. Analysis for much broader range of solutions
presented. Conclusions unchanged. Time-reversal symmetric examples ruled out,
new examples are provide
Improved lower bounds for the ground-state energy of many-body systems
New lower bounds for the binding energy of a quantum-mechanical system of
interacting particles are presented. The new bounds are expressed in terms of
two-particle quantities and improve the conventional bounds of the Hall-Post
type. They are constructed by considering not only the energy in the
two-particle system, but also the structure of the pair wave function. We apply
the formal results to various numerical examples, and show that in some cases
dramatic improvement over the existing bounds is reached.Comment: 29 pages, 5 figures, to be published in Phys. Rev.
The Shape of Gravity in a Warped Deformed Conifold
We study the spectrum of the gravitational modes in Minkowski spacetime due
to a 6-dimensional warped deformed conifold, i.e., a warped throat, in
superstring theory. After identifying the zero mode as the usual 4D graviton,
we present the KK spectrum as well as other excitation modes. Gluing the throat
to the bulk (a realistic scenario), we see that the graviton has a rather
uniform probability distribution everywhere while a KK mode is peaked in the
throat, as expected. Due to the suppressed measure of the throat in the wave
function normalization, we find that a KK mode's probability in the bulk can be
comparable to that of the graviton mode. We also present the tunneling
probabilities of a KK mode from the inflationary throat to the bulk and to
another throat. Due to resonance effect, the latter may not be suppressed as
natively expected. Implication of this property to reheating after brane
inflation is discussed
Super-extended noncommutative Landau problem and conformal symmetry
A supersymmetric spin-1/2 particle in the noncommutative plane, subject to an
arbitrary magnetic field, is considered, with particular attention paid to the
homogeneous case. The system has three different phases, depending on the
magnetic field. Due to supersymmetry, the boundary critical phase which
separates the sub- and super-critical cases can be viewed as a reduction to the
zero-energy eigensubspace. In the sub-critical phase the system is described by
the superextension of exotic Newton-Hooke symmetry, combined with the conformal
so(2,1) ~ su(1,1) symmetry; the latter is changed into so(3) ~ su(2) in the
super-critical phase. In the critical phase the spin degrees of freedom are
frozen and supersymmetry disappears.Comment: 12 pages, references added, published versio
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