18,823 research outputs found
(Extra)Ordinary Gauge Mediation
We study models of "(extra)ordinary gauge mediation," which consist of taking
ordinary gauge mediation and extending the messenger superpotential to include
all renormalizable couplings consistent with SM gauge invariance and an
R-symmetry. We classify all such models and find that their phenomenology can
differ significantly from that of ordinary gauge mediation. Some highlights
include: arbitrary modifications of the squark/slepton mass relations, small mu
and Higgsino NLSP's, and the possibility of having fewer than one effective
messenger. We also show how these models lead naturally to extremely simple
examples of direct gauge mediation, where SUSY and R-symmetry breaking occur
not in a hidden sector, but due to the dynamics of the messenger sector itself.Comment: 50 pages, 11 figure
Exact Black Hole Degeneracies and the Topological String
Motivated by the recent conjecture of Ooguri, Strominger and Vafa, we compute
the semi-canonical partition function of BPS black holes in N=4 and N=8 string
theories, to all orders in perturbation theory. Not only are the black hole
partition functions surprisingly simple; they capture the full topological
string amplitudes, as expected from the OSV conjecture. The agreement is not
perfect, however, as there are differences between the black hole and
topological string partition functions even at the perturbative level. We
propose a minimal modification of the OSV conjecture, in which these
differences are understood as a nontrivial measure factor for the topological
string.Comment: 24 page
Evidence for an intermediate mass black hole and a multi-zone warm absorber in NGC 4395
We report on the results of an analysis in the X-ray band of a recent long
ASCA observation of NGC 4395, the most variable low-luminosity AGN known. A
relativistically-broadened iron line at ~6.4 keV is clearly resolved in the
time-averaged spectrum, with an equivalent width of 310^{+70}_{-90} eV.
Time-resolved spectral analysis of the heavily absorbed soft X-ray band
confirms the existence of a variable, multi-zone warm absorber in this source,
as proposed in a previous analysis of a shorter ASCA observation. The light
curve of the source is wildly variable on timescales of hours or less, and a
factor of nearly 10 change in count-rate was recorded in a period of less than
2000 s. The long observation and variability of the source allowed the power
density spectrum (PDS) to be constructed to an unprecedented level of detail.
There is evidence for a break in the PDS from a slope of \alpha~1 to \alpha~1.8
at a frequency of around 3 \times 10^{-4} Hz. The central black hole mass of
NGC 4395 is estimated to be approximately 10^4-10^5 solar masses using the
break in the PDS, a result consistent with previous analyses using optical and
kinematical techniques.Comment: 8 pages, 6 figures, accepted for publication in MNRA
CHL Dyons and Statistical Entropy Function from D1-D5 System
We give a proof of the recently proposed formula for the dyon spectrum in CHL
string theories by mapping it to a configuration of D1 and D5-branes and
Kaluza-Klein monopole. We also give a prescription for computing the degeneracy
as a systematic expansion in inverse powers of charges. The computation can be
formulated as a problem of extremizing a duality invariant statistical entropy
function whose value at the extremum gives the logarithm of the degeneracy.
During this analysis we also determine the locations of the zeroes and poles of
the Siegel modular forms whose inverse give the dyon partition function in the
CHL models.Comment: LaTeX file, 48 pages; v2: typos correcte
Dyon Spectrum in CHL Models
We propose a formula for the degeneracy of quarter BPS dyons in a class of
CHL models. The formula uses a modular form of a subgroup of the genus two
modular group Sp(2,Z). Our proposal is S-duality invariant and reproduces
correctly the entropy of a dyonic black hole to first non-leading order for
large values of the charges.Comment: LaTeX file, 38 pages, minor changes in section 3.3(v2), minor changes
in introduction, appendix A and C(v3
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