290 research outputs found
Counting Giant Gravitons in AdS_3
We quantize the set of all quarter BPS brane probe solutions in global AdS_3
\times S^3 \times T^4/K3 found in arxiv:0709.1168 [hep-th]. We show that,
generically, these solutions give rise to states in discrete representations of
the SL(2,R) WZW model on AdS_3. Our procedure provides us with a detailed
description of the low energy 1/4 and 1/2 BPS sectors of string theory on this
background. The 1/4 BPS partition function jumps as we move off the point in
moduli space where the bulk theta angle and NS-NS fields vanish. We show that
generic 1/2 BPS states are protected because they correspond to geodesics
rather than puffed up branes. By exactly quantizing the simplest of the probes
above, we verify our description of 1/4 BPS states and find agreement with the
known spectrum of 1/2 BPS states of the boundary theory. We also consider the
contribution of these probes to the elliptic genus and discuss puzzles, and
their possible resolutions, in reproducing the elliptic genus of the symmetric
product.Comment: 47 pages; (v2) references and minor clarifications adde
Contemporary Natural Philosophy and Philosophies—Part 2
This is a short presentation by the Guest Editors of the series of Special Issues of the journal Philosophies under the common title "Contemporary Natural Philosophy and Philosophies" in which we present Part 2. The series will continue, and the call for contributions to the next Special Issue will appear shortly
Alpha decay and proton-neutron correlations
We study the influence of proton-neutron (p-n) correlations on alpha-decay
width. It is shown from the analysis of alpha Q values that the p-n
correlations increase the penetration of the alpha particle through the Coulomb
barrier in the treatment following Gamow's formalism, and enlarges the total
alpha-decay width significantly.
In particular, the isoscalar p-n interactions play an essential role in
enlarging the alpha-decay width.
The so-called "alpha-condensate" in Z > 84 isotopes are related to the strong
p-n correlations.Comment: 5 pages, 6 figures, accepted for publication in Phys. Rev. C (R.C.
A realisation of Lorentz algebra in Lorentz violating theory
A Lorentz non-invariant higher derivative effective action in flat spacetime,
characterised by a constant vector, can be made invariant under infinitesimal
Lorentz transformations by restricting the allowed field configurations. These
restricted fields are defined as functions of the background vector in such a
way that background dependance of the dynamics of the physical system is no
longer manifest. We show here that they also provide a field basis for the
realisation of Lorentz algebra and allow the construction of a Poincar\'e
invariant symplectic two form on the covariant phase space of the theory.Comment: text body edited, reference adde
Currents and Superpotentials in classical gauge theories: II. Global aspects and the example of Affine gravity
The conserved charges associated to gauge symmetries are defined at a
boundary component of space-time because the corresponding Noether current can
be rewritten on-shell as the divergence of a superpotential. However, the
latter is afflicted by ambiguities. Regge and Teitelboim found a procedure to
lift the arbitrariness in the Hamiltonian framework. An alternative covariant
formula was proposed by one of us for an arbitrary variation of the
superpotential, it depends only on the equations of motion and on the gauge
symmetry under consideration. Here we emphasize that in order to compute the
charges, it is enough to stay at a boundary of spacetime, without requiring any
hypothesis about the bulk or about other boundary components, so one may speak
of holographic charges. It is well known that the asymptotic symmetries that
lead to conserved charges are really defined at infinity, but the choice of
boundary conditions and surface terms in the action and in the charges is
usually determined through integration by parts whereas each component of the
boundary should be considered separately. We treat the example of gravity (for
any space-time dimension, with or without cosmological constant), formulated as
an Affine theory which is a natural generalization of the Palatini and
Cartan-Weyl (vielbein) first order formulations. We then show that the
superpotential associated to a Dirichlet boundary condition on the metric (the
one needed to treat asymptotically flat or AdS spacetimes) is the one proposed
by Katz, Bi\u{c}{\'a}k and Lynden-Bell and not that of Komar. We finally
discuss the KBL superpotential at null infinity.Comment: 16 pages, minor corrections and references added. Final version to
appear in CQ
Quantum Cosmological Approach to 2d Dilaton Gravity
We study the canonical quantization of the induced 2d-gravity and the pure
gravity CGHS-model on a closed spatial section. The Wheeler-DeWitt equations
are solved in (spatially homogeneous) choices of the internal time variable and
the space of solutions is properly truncated to provide the physical Hilbert
space. We establish the quantum equivalence of both models and relate the
results with the covariant phase-space quantization. We also discuss the
relation between the quantum wavefunctions and the classical space-time
solutions and propose the wave function representing the ground state.Comment: 19 pages, 2 figures (uuencoded) included, plain Latex, needs
amssymb.sty and psfig.sty, FTUV/93-34 & IFIC/93-3
Holography in asymptotically flat space-times and the BMS group
In a previous paper (hep-th/0306142) we have started to explore the
holographic principle in the case of asymptotically flat space-times and
analyzed in particular different aspects of the Bondi-Metzner-Sachs (BMS)
group, namely the asymptotic symmetry group of any asymptotically flat
space-time. We continue this investigation in this paper. Having in mind a
S-matrix approach with future and past null infinity playing the role of
holographic screens on which the BMS group acts, we connect the IR sectors of
the gravitational field with the representation theory of the BMS group. We
analyze the (complicated) mapping between bulk and boundary symmetries pointing
out differences with respect to the AdS/CFT set up. Finally we construct a BMS
phase space and a free hamiltonian for fields transforming w.r.t BMS
representations. The last step is supposed to be an explorative investigation
of the boundary data living on the degenerate null manifold at infinity.Comment: 31 pages, several changes in section 3 and 7 and references update
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