524 research outputs found
Magnetic Charge Can Locally Stabilize Kaluza-Klein Bubbles
We construct a new 2-parameter family of static topological solitons in 5D
minimal supergravity which are endowed with magnetic charge and mass. The
solitons are asymptotically , where the radius of the
has a lower bound . Setting up initial data on a Cauchy
slice at a moment of time symmetry, we demonstrate that if these
solitons correspond to a perturbatively stable "small" static bubble as well as
an unstable "large" static bubble, whereas if there are no static
bubbles. The energetics and thermodynamics of the magnetic black string are
then discussed and it is shown that the locally stable bubble is the end point
of a phase transition for an appropriate range of black string parameters.Comment: 5 pages, 1 figure. v3: references and stringy discussion added, v4:
introduction expanded. Minor comments throughout. Accepted for publication in
PL
Solving the Hierarchy Problem with Noncompact Extra Dimensions
We show that gravitational effects of global cosmic 3-branes can be
responsible for compactification from six to four space-time dimensions,
naturally producing the observed hierarchy between electroweak and
gravitational forces. The finite radius of the transverse dimensions follows
from Einstein's equation, and is exponentially large compared with the scales
associated with the 3-brane. The space-time ends on a mild naked singularity at
the boundary of the transverse dimensions; nevertheless unitary boundary
conditions render the singularity harmless.Comment: 11 pages. Several references adde
Charged Dilaton Black Holes with Unusual Asymptotics
We present a new class of black hole solutions in Einstein-Maxwell-dilaton
gravity in dimensions. These solutions have regular horizons and a
singularity only at the origin. Their asymptotic behavior is neither
asymptotically flat nor (anti-) de Sitter. Similar solutions exist for certain
Liouville-type potentials for the dilaton.Comment: 24 pages, harvmac.tex, no figure
Classical and Thermodynamic Stability of Black Branes
It is argued that many non-extremal black branes exhibit a classical
Gregory-Laflamme instability if, and only if, they are locally
thermodynamically unstable. For some black branes, the Gregory-Laflamme
instability must therefore disappear near extremality. For the black -branes
of the type II supergravity theories, the Gregory-Laflamme instability
disappears near extremality for but persists all the way down to
extremality for (the black D3-brane is not covered by the analysis of
this paper). This implies that the instability also vanishes for the
near-extremal black M2 and M5-brane solutions.Comment: 21 pages, LaTeX. v2: Various points clarified, typos corrected and
reference adde
Correlations between black holes formed in cosmic string breaking
An analysis of cosmic string breaking with the formation of black holes
attached to the ends reveals a remarkable feature: the black holes can be
correlated or uncorrelated. We find that, as a consequence, the
number-of-states enhancement factor in the action governing the formation of
uncorrelated black holes is twice the one for a correlated pair. We argue that
when an uncorrelated pair forms at the ends of the string, the physics involved
is more analogous to thermal nucleation than to particle-antiparticle creation.
Also, we analyze the process of intercommuting strings induced by black hole
annihilation and merging. Finally, we discuss the consequences for grand
unified strings. The process whereby uncorrelated black holes are formed yields
a rate which significantly improves over those previously considered, but still
not enough to modify string cosmology.Comment: 11 pages, LaTeX. Final version, to appear in Phys. Rev.
Gauss-Bonnet Black Holes and Heavy Fermion Metals
We consider charged black holes in Einstein-Gauss-Bonnet Gravity with
Lifshitz boundary conditions. We find that this class of models can reproduce
the anomalous specific heat of condensed matter systems exhibiting
non-Fermi-liquid behaviour at low temperatures. We find that the temperature
dependence of the Sommerfeld ratio is sensitive to the choice of Gauss-Bonnet
coupling parameter for a given value of the Lifshitz scaling parameter. We
propose that this class of models is dual to a class of models of
non-Fermi-liquid systems proposed by Castro-Neto et.al.Comment: 17 pages, 6 figures, pdfLatex; small corrections to figure 10 in this
versio
Thermodynamic instability of doubly spinning black objects
We investigate the thermodynamic stability of neutral black objects with (at
least) two angular momenta. We use the quasilocal formalism to compute the
grand canonical potential and show that the doubly spinning black ring is
thermodynamically unstable. We consider the thermodynamic instabilities of
ultra-spinning black objects and point out a subtle relation between the
microcanonical and grand canonical ensembles. We also find the location of the
black string/membrane phases of doubly spinning black objects.Comment: 25 pages, 7 figures v2: matches the published versio
Brick Walls on the Brane
The so-called ``brick-wall model'' is a semi-classical approach that has been
used to explain black hole entropy in terms of thermal matter fields. Here, we
apply the brick-wall formalism to thermal bulk fields in a Randall-Sundrum
brane world scenario. In this case, the black hole entity is really a
string-like object in the anti-de Sitter bulk, while appearing as a
Schwarzchild black hole to observers living on the brane. In spite of these
exotic circumstances, we establish that the Bekenstein-Hawking entropy law is
preserved. Although a similar calculation was recently considered in the
literature, this prior work invoked a simplifying assumption (which we avoid)
that can not be adequately justified.Comment: 18 pages, Latex; references and discussion added but conclusions
unchanged; references missing in V4 have been restore
Folate catabolites in spot urine as non-invasive biomarkers of folate status during habitual intake and folic acid supplementation.
Folate status, as reflected by red blood cell (RCF) and plasma folates (PF), is related to health and disease risk. Folate degradation products para-aminobenzoylglutamate (pABG) and para-acetamidobenzoylglutamate (apABG) in 24 hour urine have recently been shown to correlate with blood folate.
Since blood sampling and collection of 24 hour urine are cumbersome, we investigated whether the determination of urinary folate catabolites in fasted spot urine is a suitable non-invasive biomarker for folate status in subjects before and during folic acid supplementation.
Immediate effects of oral folic acid bolus intake on urinary folate catabolites were assessed in a short-term pre-study. In the main study we included 53 healthy men. Of these, 29 were selected for a 12 week folic acid supplementation (400 µg). Blood, 24 hour and spot urine were collected at baseline and after 6 and 12 weeks and PF, RCF, urinary apABG and pABG were determined.
Intake of a 400 µg folic acid bolus resulted in immediate increase of urinary catabolites. In the main study pABG and apABG concentrations in spot urine correlated well with their excretion in 24 hour urine. In healthy men consuming habitual diet, pABG showed closer correlation with PF (rs = 0.676) and RCF (rs = 0.649) than apABG (rs = 0.264, ns and 0.543). Supplementation led to significantly increased folate in plasma and red cells as well as elevated urinary folate catabolites, while only pABG correlated significantly with PF (rs = 0.574) after 12 weeks.
Quantification of folate catabolites in fasted spot urine seems suitable as a non-invasive alternative to blood or 24 hour urine analysis for evaluation of folate status in populations consuming habitual diet. In non-steady-state conditions (folic acid supplementation) correlations between folate marker (RCF, PF, urinary catabolites) decrease due to differing kinetics
Rotating black holes with equal-magnitude angular momenta in d=5 Einstein-Gauss-Bonnet theory
We construct rotating black hole solutions in Einstein-Gauss-Bonnet theory in
five spacetime dimensions. These black holes are asymptotically flat, and
possess a regular horizon of spherical topology and two equal-magnitude angular
momenta associated with two distinct planes of rotation. The action and global
charges of the solutions are obtained by using the quasilocal formalism with
boundary counterterms generalized for the case of Einstein-Gauss-Bonnet theory.
We discuss the general properties of these black holes and study their
dependence on the Gauss-Bonnet coupling constant . We argue that most
of the properties of the configurations are not affected by the higher
derivative terms. For fixed the set of black hole solutions terminates
at an extremal black hole with a regular horizon, where the Hawking temperature
vanishes and the angular momenta attain their extremal values. The domain of
existence of regular black hole solutions is studied. The near horizon geometry
of the extremal solutions is determined by employing the entropy function
formalism.Comment: 25 pages, 7 figure
- …