2,831 research outputs found
Uniqueness of Nash equilibria in quantum Cournot duopoly game
A quantum Cournot game of which classical form game has multiple Nash
equilibria is examined. Although the classical equilibria fail to be Pareto
optimal, the quantum equilibrium exhibits the following two properties, (i) if
the measurement of entanglement between strategic variables chosen by the
competing firms is sufficiently large, the multiplicity of equilibria vanishes,
and, (ii) the more strongly the strategic variables are entangled, the more
closely the unique equilibrium approaches to the optimal one.Comment: 7 pages, 2 figure
Asymptotically hyperbolic manifolds with small mass
For asymptotically hyperbolic manifolds of dimension with scalar
curvature at least equal to the conjectured positive mass theorem
states that the mass is non-negative, and vanishes only if the manifold is
isometric to hyperbolic space. In this paper we study asymptotically hyperbolic
manifolds which are also conformally hyperbolic outside a ball of fixed radius,
and for which the positive mass theorem holds. For such manifolds we show that
the conformal factor tends to one as the mass tends to zero
Positive tension 3-branes in an bulk
In this work, we review and extend the so-called consistency conditions for
the existence of a braneworld scenario in arbitrary dimensions in the
Brans-Dicke (BD) gravitational theory. After that, we consider the particular
case of a five-dimensional scenario which seems to have phenomenological
interesting implications. We show that, in the BD framework, it is possible to
achieve necessary conditions pointing to the possibility of accommodating
branes with positive tensions in an AdS bulk by the presence of the additional
BD scalar field, avoiding in this way the necessity of including unstable
objects in the compactification scheme. Furthermore, in the context of time
variable brane tension, it is shown that the brane tension may change its sign,
following the bulk cosmological constant sign.Comment: 15 pages, new version to appear in JHE
The Measure for the Multiverse and the Probability for Inflation
We investigate the measure problem in the framework of inflationary
cosmology. The measure of the history space is constructed and applied to
inflation models. Using this measure, it is shown that the probability for the
generalized single field slow roll inflation to last for e-folds is
suppressed by a factor , and the probability for the generalized
-field slow roll inflation is suppressed by a much larger factor
. Some non-inflationary models such as the cyclic model do not
suffer from this difficulty.Comment: 16 page
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
Off-shell extension of S-matrix elements and tachyonic effective actions
We show that the on-shell S-matrix elements of four open string massless
scalars, two scalars and two tachyons, and four open string tachyons in the
super string theory can be written in a unique form. We then propose an
off-shell extension for the S-matrix element of four scalars which is
consistent, in the low energy limit, with the Dirac-Born-Infeld effective
action. Using a similar off-shell extension for the S-matrix element of two
scalars and two tachyons and for the S-matrix element of four tachyons, we show
that they are fully consistent with the tachyonic DBI action.Comment: Latex, 17 pages, v3:a paragraph comparing off-shell and on- shell
amplitudes added, reference adde
Particle Motion Around Tachyon Monopole
Recently, Li and Liu have studied global monoole of tachyon in a four
dimensional static space-time. We analyze the motion of massless and massive
particles around tachyon monopole. Interestingly, for the bending of light rays
due to tachyon monopole instead of getting angle of deficit we find angle of
surplus. Also we find that the tachyon monopole exerts an attractive
gravitational force towards matter.Comment: 14 pages, 7 figure
Noncommutative Topological Theories of Gravity
The possibility of noncommutative topological gravity arising in the same
manner as Yang-Mills theory is explored. We use the Seiberg-Witten map to
construct such a theory based on a SL(2,C) complex connection, from which the
Euler characteristic and the signature invariant are obtained. This gives us a
way towards the description of noncommutative gravitational instantons as well
as noncommutative local gravitational anomalies.Comment: 17+1 pages, LaTeX, no figures, some clarifications, comments and
references added, style improve
Non- symmetric braneworlds in scalar tensorial gravity
We obtain, via the Gauss-Codazzi formalism, the expression of the effective
Einstein-Brans-Dicke projected equations in a non- symmetric
braneworld scenario which presents hybrid compactification. It is shown that
the functional form of such equations resembles the one in the Einstein's case,
except by the fact that they bring extra informations in the context of exotic
compactifications.Comment: 12 pages, LATEX file, no figures. Accepted for publication in the
European Physical Journal
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