195 research outputs found
Greybody Factors and Charges in Kerr/CFT
We compute greybody factors for near extreme Kerr black holes in D=4 and D=5.
In D=4 we include four charges so that our solutions can be continuously
deformed to the BPS limit. In D=5 we include two independent angular momenta so
Left-Right symmetry is incorporated. We discuss the CFT interpretation of our
emission amplitudes, including the overall frequency dependence and the
dependence on all black hole parameters. We find that all additional parameters
can be incorporated Kerr/CFT, with central charge independent of U(1) charges.Comment: 27 pages. v2: typos fixed, references adde
Black Holes in Supergravity: the non-BPS Branch
We construct extremal, spherically symmetric black hole solutions to 4D
supergravity with charge assignments that preclude BPS-saturation. In
particular, we determine the ground state energy as a function of charges and
moduli. We find that the mass of the non-BPS black hole remains that of a
marginal bound state of four basic constituents throughout the entire moduli
space and that there is always a non-zero gap above the BPS bound.Comment: 29 pages, one appendix, no figures; v2. few comments and references
added and a missing sign included; v3. further references adde
5D Black Holes and Strings with Higher Derivatives
We find asymptotically flat black hole and string solutions to 5D
supergravity in the presence of higher derivative terms. In some cases,
including the fundamental heterotic string solution, the higher derivative
terms smooth out naked singularities into regular geometries carrying zero
entropy. We also compute corrections to the entropy of 5D Calabi-Yau black
holes, and discuss the relation to previous results.Comment: 33 pages, 2 figs., harvmac; v2: typos corrected, references added v3:
refs correcte
Separability of Black Holes in String Theory
We analyze the origin of separability for rotating black holes in string
theory, considering both massless and massive geodesic equations as well as the
corresponding wave equations. We construct a conformal Killing-Stackel tensor
for a general class of black holes with four independent charges, then identify
two-charge configurations where enhancement to an exact Killing-Stackel tensor
is possible. We show that further enhancement to a conserved Killing-Yano
tensor is possible only for the special case of Kerr-Newman black holes. We
construct natural null congruences for all these black holes and use the
results to show that only the Kerr-Newman black holes are algebraically special
in the sense of Petrov. Modifying the asymptotic behavior by the subtraction
procedure that induces an exact SL(2)^2 also preserves only the conformal
Killing-Stackel tensor. Similarly, we find that a rotating Kaluza-Klein black
hole possesses a conformal Killing-Stackel tensor but has no further
enhancements.Comment: 27 page
Citizen Seismology in the Arctic
Landslides, earthquakes and other natural disasters are expected to increase in the Arctic, yet our ability to make informed decisions about safety is tightly limited by lack of data. As part of the Integrated Arctic Observation System (INTAROS) project, geophones were installed by residents in Greenland and by University of Bergen in Svalbard in 2018. The purpose of the installations was to explore challenges and benefits of community-based data collection for seismological monitoring in the Arctic region. Raspberry Shake units with one/three-component velocity sensors were selected for the deployment, due to their user-friendly configuration, easy installation, and well established digital platform and web services. The purpose of engaging community members in the use of geophone sensors was to monitor earthquakes, cryoseisms (events generated by ice mass), and landslides. We report our findings with respect to challenges regarding the installation and operation of the Raspberry Shake sensors at both locations. Connecting community-based recordings with permanent seismological networks improved both the detection capability and the data support for understanding seismic events in Greenland. In contrast, finding suitable locations for deployments in Longyearbyen turned out to be challenging, because most buildings are constructed on poles due to the permafrost and indoor space is expensive. Promoting citizen seismology in the Arctic could improve monitoring of seismic events in the Arctic while simultaneously raising community awareness of natural hazards.publishedVersio
Resolution of Cosmological Singularities
We show that a class of 3+1 dimensional Friedmann-Robertson-Walker
cosmologies can be embedded within a variety of solutions of string theory. In
some realizations the apparent singularities associated with the big bang or
big crunch are resolved at non-singular horizons of higher-dimensional
quasi-black hole solutions (with compactified real time); in others plausibly
they are resolved at D-brane bound states having no conventional space-time
interpretation.Comment: 11 pages, latex. Two references added, one typo correcte
Heterotic Flux Attractors
We find attractor equations describing moduli stabilization for heterotic
compactifications with generic SU(3)-structure. Complex structure and K\"ahler
moduli are treated on equal footing by using SU(3)xSU(3)-structure at
intermediate steps. All independent vacuum data, including VEVs of the
stabilized moduli, is encoded in a pair of generating functions that depend on
fluxes alone. We work out an explicit example that illustrates our methods.Comment: 37 pages, references and clarifications adde
Squeezed States in the de Sitter Vacuum
We discuss the treatment of squeezed states as excitations in the Euclidean
vacuum of de Sitter space. A comparison with the treatment of these states as
candidate no-particle states, or alpha-vacua, shows important differences
already in the free theory. At the interacting level alpha-vacua are
inconsistent, but squeezed state excitations seem perfectly acceptable. Indeed,
matrix elements can be renormalized in the excited states using precisely the
standard local counterterms of the Euclidean vacuum. Implications for
inflationary scenarios in cosmology are discussed.Comment: 15 pages, no figures. One new citation in version 3; no other change
Conformal Symmetry for Black Holes in Four Dimensions
We show that the asymptotic boundary conditions of general asymptotically
flat black holes in four dimensions can be modified such that a conformal
symmetry emerges. The black holes with the asymptotic geometry removed in this
manner satisfy the equations of motion of minimal supergravity in five
dimensions. We develop evidence that a two dimensional CFT dual of general
black holes in four dimensions account for their black hole entropy.Comment: 24 pages, minor correction
5D Attractors with Higher Derivatives
We analyze higher derivative corrections to attractor geometries in five
dimensions. We find corrected AdS_3xS^2 geometries by solving the equations of
motion coming from a recently constructed four-derivative supergravity action
in five dimensions. The result allows us to explicitly verify a previous
anomaly based derivation of the AdS_3 central charges of this theory. Also, by
dimensional reduction we compare our results with those of the 4D higher
derivative attractor, and find complete agreement.Comment: 18 pages, harvma
- âŠ