1,204 research outputs found
On walls of marginal stability in N=2 string theories
We study the properties of walls of marginal stability for BPS decays in a
class of N=2 theories. These theories arise in N=2 string compactifications
obtained as freely acting orbifolds of N=4 theories, such theories include the
STU model and the FHSV model. The cross sections of these walls for a generic
decay in the axion-dilaton plane reduce to lines or circles. From the
continuity properties of walls of marginal stability we show that central
charges of BPS states do not vanish in the interior of the moduli space. Given
a charge vector of a BPS state corresponding to a large black hole in these
theories, we show that all walls of marginal stability intersect at the same
point in the lower half of the axion-dilaton plane. We isolate a class of
decays whose walls of marginal stability always lie in a region bounded by
walls formed by decays to small black holes. This enables us to isolate a
region in moduli space for which no decays occur within this class. We then
study entropy enigma decays for such models and show that for generic values of
the moduli, that is when moduli are of order one compared to the charges,
entropy enigma decays do not occur in these models.Comment: 40 pages, 2 figure
Comments on Charges and Near-Horizon Data of Black Rings
We study how the charges of the black rings measured at the asymptotic
infinity are encoded in the near-horizon metric and gauge potentials,
independent of the detailed structure of the connecting region. Our analysis
clarifies how different sets of four-dimensional charges can be assigned to a
single five-dimensional object under the Kaluza-Klein reduction. Possible
choices are related by the Witten effect on dyons and by the large gauge
transformation in four and five dimensions, respectively.Comment: 30 pages, 1 figure; v2: additional references; v3: published versio
On Entropy Function for Supersymmetric Black Rings
The entropy function for five-dimensional supersymmetric black rings, which
are solutions of minimal supergravity, is calculated via both
on-shell and off-shell formalism. We find that at the tree level, the entropy
function obtained from both perspectives can reproduce the Bekenstein-Hawking
entropy. We also compute the higher order corrections to the entropy arising
form five-dimensional Gauss-Bonnet term as well as supersymmetric
completion respectively and compare the results with previous microscopic
calculations.Comment: 17 pages, no figure, JHEP3 style, to appear in JHEP
On R**2 Corrections for 5D Black Holes
We study higher order corrections to extremal black holes/black string in
five dimensions. These higher order corrections are due to supersymmetric
completion of R**2 term in five dimensions. By making use of the results we
extend the notion of very special geometry when higher derivative terms are
also taken into account. This can be used to make a connection between total
bundle space of near horizon wrapped M2's and wrapped M5's in the presence of
higher order corrections. We also show how the corrected geometry removes the
singularity of a small black hole.Comment: 16 pages, latex file, V3: typos corrected, refs added, V4; minor
corrections, few comments added, refs adde
Extremal black holes in D=5: SUSY vs. Gauss-Bonnet corrections
We analyse near-horizon solutions and compare the results for the black hole
entropy of five-dimensional spherically symmetric extremal black holes when the
N=2 SUGRA actions are supplied with two different types of higher-order
corrections: (1) supersymmetric completion of gravitational Chern-Simons term,
and (2) Gauss-Bonnet term. We show that for large BPS black holes lowest order
\alpha' corrections to the entropy are the same, but for non-BPS are generally
different. We pay special attention to the class of prepotentials connected
with K3\times T^2 and T^6 compactifications. For supersymmetric correction we
find beside BPS also a set of non-BPS solutions. In the particular case of T^6
compactification (equivalent to the heterotic string on ) we
find the (almost) complete set of solutions (with exception of some non-BPS
small black holes), and show that entropy of small black holes is different
from statistical entropy obtained by counting of microstates of heterotic
string theory. We also find complete set of solutions for K3\times T^2 and T^6
case when correction is given by Gauss-Bonnet term. Contrary to
four-dimensional case, obtained entropy is different from the one with
supersymmetric correction. We show that in Gauss-Bonnet case entropy of small
``BPS'' black holes agrees with microscopic entropy in the known cases.Comment: 28 pages; minor changes, version to appear in JHE
Logarithmic Corrections to Rotating Extremal Black Hole Entropy in Four and Five Dimensions
We compute logarithmic corrections to the entropy of rotating extremal black
holes using quantum entropy function i.e. Euclidean quantum gravity approach.
Our analysis includes five dimensional supersymmetric BMPV black holes in type
IIB string theory on T^5 and K3 x S^1 as well as in the five dimensional CHL
models, and also non-supersymmetric extremal Kerr black hole and slowly
rotating extremal Kerr-Newmann black holes in four dimensions. For BMPV black
holes our results are in perfect agreement with the microscopic results derived
from string theory. In particular we reproduce correctly the dependence of the
logarithmic corrections on the number of U(1) gauge fields in the theory, and
on the angular momentum carried by the black hole in different scaling limits.
We also explain the shortcomings of the Cardy limit in explaining the
logarithmic corrections in the limit in which the (super)gravity description of
these black holes becomes a valid approximation. For non-supersymmetric
extremal black holes, e.g. for the extremal Kerr black hole in four dimensions,
our result provides a stringent testing ground for any microscopic explanation
of the black hole entropy, e.g. Kerr/CFT correspondence.Comment: LaTeX file, 50 pages; v2: added extensive discussion on the relation
between boundary condition and choice of ensemble, modified analysis for
slowly rotating black holes, all results remain unchanged, typos corrected;
v3: minor additions and correction
Rice F-bZIP transcription factors regulate the zinc deficiency response
The F-bZIP transcription factors bZIP19 and bZIP23 are the central regulators of the zinc deficiency response in Arabidopsis, and phylogenetic analysis of F-bZIP homologs across land plants indicates that the regulatory mechanism of the zinc deficiency response may be conserved. Here, we identified the rice F-bZIP homologs and investigated their function. OsbZIP48 and OsbZIP50, but not OsbZIP49, complement the zinc deficiency-hypersensitive Arabidopsis bzip19bzip23 double mutant. Ectopic expression of OsbZIP50 in Arabidopsis significantly increases plant zinc accumulation under control zinc supply, suggesting an altered Zn sensing in OsbZIP50. In addition, we performed a phylogenetic analysis of F-bZIP homologs from representative monocot species that supports the branching of plant F-bZIPs into Group 1 and Group 2. Our results suggest that regulation of the zinc deficiency response in rice is conserved, with OsbZIP48 being a functional homolog of AtbZIP19 and AtbZIP23. A better understanding of the mechanisms behind the Zn deficiency response in rice and other important crops will contribute to develop plant-based strategies to address the problems of Zn deficiency in soils, crops, and cereal-based human diets.</p
Sub-terahertz, microwaves and high energy emissions during the December 6, 2006 flare, at 18:40 UT
The presence of a solar burst spectral component with flux density increasing
with frequency in the sub-terahertz range, spectrally separated from the
well-known microwave spectral component, bring new possibilities to explore the
flaring physical processes, both observational and theoretical. The solar event
of 6 December 2006, starting at about 18:30 UT, exhibited a particularly
well-defined double spectral structure, with the sub-THz spectral component
detected at 212 and 405 GHz by SST and microwaves (1-18 GHz) observed by the
Owens Valley Solar Array (OVSA). Emissions obtained by instruments in
satellites are discussed with emphasis to ultra-violet (UV) obtained by the
Transition Region And Coronal Explorer (TRACE), soft X-rays from the
Geostationary Operational Environmental Satellites (GOES) and X- and gamma-rays
from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The sub-THz
impulsive component had its closer temporal counterpart only in the higher
energy X- and gamma-rays ranges. The spatial positions of the centers of
emission at 212 GHz for the first flux enhancement were clearly displaced by
more than one arc-minute from positions at the following phases. The observed
sub-THz fluxes and burst source plasma parameters were found difficult to be
reconciled to a purely thermal emission component. We discuss possible
mechanisms to explain the double spectral components at microwaves and in the
THz ranges.Comment: Accepted version for publication in Solar Physic
Naturalness and theoretical constraints on the Higgs boson mass
Arbitrary regularization dependent parameters in Quantum Field Theory are
usually fixed on symmetry or phenomenology grounds. We verify that the
quadratically divergent behavior responsible for the lack of naturalness in the
Standard Model (SM) is intrinsically arbitrary and regularization dependent.
While quadratic divergences are welcome for instance in effective models of low
energy QCD, they pose a problem in the SM treated as an effective theory in the
Higgs sector. Being the very existence of quadratic divergences a matter of
debate, a plausible scenario is to search for a symmetry requirement that could
fix the arbitrary coefficient of the leading quadratic behavior to the Higgs
boson mass to zero. We show that this is possible employing consistency of
scale symmetry breaking by quantum corrections. Besides eliminating a
fine-tuning problem and restoring validity of perturbation theory, this
requirement allows to construct bounds for the Higgs boson mass in terms of
(where is the renormalized Higgs mass and
is the 1-loop Higgs mass correction). Whereas
(perturbative regime) in this scenario allows the Higgs boson mass around the
current accepted value, the inclusion of the quadratic divergence demands
arbitrarily large to reach that experimental value.Comment: 6 pages, 4 figure
Observation of the Higgs Boson of strong interaction via Compton scattering by the nucleon
It is shown that the Quark-Level Linear Model (QLLM) leads
to a prediction for the diamagnetic term of the polarizabilities of the nucleon
which is in excellent agreement with the experimental data. The bare mass of
the meson is predicted to be MeV and the two-photon
width keV. It is argued that the
mass predicted by the QLLM corresponds to the reaction, i.e. to a -channel pole of the reaction.
Large -angle Compton scattering experiments revealing effects of the
meson in the differential cross section are discussed. Arguments are presented
that these findings may be understood as an observation of the Higgs boson of
strong interaction while being part of the constituent quark.Comment: 17 pages, 6 figure
- …