152 research outputs found
Membranes on Calibrations
M2-branes can blow up into BPS funnels that end on calibrated intersections
of M5-branes. In this quick note, we make the observation that the constraints
required for the consistency of these solutions are automatic in
Bagger-Lambert-Gustavsson (BLG) theory, thanks to the fundamental identity and
the supersymmetry of the calibration. We use this to explain how the previous
ad hoc fuzzy funnel constructions emerge in this picture, and make some
comments about the role of the 3-algebra trace form in the derivation.Comment: 9 pages, no figures; references added, minor change
A Comment on Kerr-CFT and Wald Entropy
We point out that the entropies of black holes in general diffeomorphism
invariant theories, computed using the Kerr-CFT correspondence and the Wald
formula (as implemented in the entropy function formalism), need not always
agree. A simple way to illustrate this is to consider Einstein-Gauss-Bonnet
gravity in four dimensions, where the Gauss-Bonnet term is topological. This
means that the central charge of Kerr-CFT computed in the
Barnich-Brandt-Compere formalism remains the same as in Einstein gravity, while
the entropy computed using the entropy function gives a universal correction
proportional to the Gauss-Bonnet coupling. We argue that at least in this
example, the Kerr-CFT result is the physically reasonable one. The resolution
to this discrepancy might lie in a better understanding of boundary terms.Comment: 11 pages, v2,3: refs added, minor change
Desingularization of the Milne Universe
Resolution of cosmological singularities is an important problem in any full
theory of quantum gravity. The Milne orbifold is a cosmology with a
big-bang/big-crunch singularity, but being a quotient of flat space it holds
potential for resolution in string theory. It is known however, that some
perturbative string amplitudes diverge in the Milne geometry. Here we show that
flat space higher spin theories can effect a simple resolution of the Milne
singularity when one embeds the latter in 2+1 dimensions. We explain how to
reconcile this with the expectation that non-perturbative string effects are
required for resolving Milne. Along the way, we introduce a Grassmann
realization of the \.{I}n\"on\"u-Wigner contraction to export much of the AdS
technology to our flat space computation.Comment: 4 pages, revtex, v2: minor clarifications/corrections, refs added,
v3: minor error corrected, v4: published PLB version (essentially
A Note on D1-D5 Entropy and Geometric Quantization
We quantize the space of 2-charge fuzzballs in IIB supergravity on . The
resulting entropy precisely matches the D1-D5 black hole entropy, including a
specific numerical coefficient. A partial match (ie., a smaller coefficient)
was found by Rychkov a decade ago using the Lunin-Mathur subclass of solutions
- we use a simple observation to generalize his approach to the full moduli
space of fuzzballs, filling a small gap in the literature.Comment: v2,3: minor corrections to a footnote and acknowledgments, v1 is the
JHEP versio
Higher Spin Resolution of a Toy Big Bang
Diffeomorphisms preserve spacetime singularities, whereas higher spin
symmetries need not. Since three dimensional de Sitter space has quotients that
have big-bang/big-crunch singularities and since dS_3-gravity can be written as
an SL(2,C) Chern-Simons theory, we investigate SL(3,C) Chern-Simons theory as a
higher-spin context in which these singularities might get resolved. As in the
case of higher spin black holes in AdS_3, the solutions are invariantly
characterized by their holonomies. We show that the dS_3 quotient singularity
can be de-singularized by an SL(3,C) gauge transformation that preserves the
holonomy: this is a higher spin resolution the cosmological singularity. Our
work deals exclusively with the bulk theory, and is independent of the
subtleties involved in defining a CFT_2 dual to dS_3 in the sense of dS/CFT.Comment: v2-v3: typos removed, refs added. v4: minor improvements, Phys Rev D
version, v5: one more typo fixed, footnote adde
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