280 research outputs found
One-Loop Supergravity Corrections to the Black Hole Entropy and Residual Supersymmetry
We study the one-loop corrections to the effective on-shell action of N=2
supergravity in the background of the Reissner-Nordstrom black hole. In the
extreme case the contributions from graviton, gravitino and photon to the
one-loop corrections to the entropy are shown to cancel. This gives the first
explicit example of the supersymmetric non-renormalization theorem for the
on-shell action (entropy) for BPS configurations which admit Killing spinors.
We display the residual supersymmetry of the perturbations of a general
supersymmetric theory in a bosonic BPS background.Comment: 13 Pages, LaTe
On scattering off the extreme Reissner-Nordstr\"om black hole in N=2 supergravity
The scattering amplitudes for the perturbed fields of the N=2 supergravity
about the extreme Reissner-Nordstr\"om black hole is examined. Owing to the
fact that the extreme hole is a BPS state of the theory and preserves an
unbroken global supersymmetry(N=1), the scattering amplitudes of the component
fields should be related to each other. In this paper, we derive the formula of
the transformation of the scattering amplitudes.Comment: 9 pages, revtex, no figures, a few typing errors correcte
Superconductivity in Na_xCoO_2yH_2O by charge fluctuation
A new mechanism for superconductivity in the newly discovered Co-based oxide
is proposed by using charge fluctuation. A single-band extended Hubbard model
on the triangular lattice is studied within random phase approximation.
-wave triplet superconductivity is stabilized in the vicinity of
charge-density-wave instability, which is in sharp contrast with the
square-lattice case. The physical origin of the realization of the -wave
triplet state as well as the relevance to experiments are discussed
Superconductivity in the Three-Fold Charge-Ordered Metal of the Triangular-Lattice Extended Hubbard Model
The quarter-filling extended Hubbard model on the triangular lattice is
studied to explore pairing instability in the three-fold charge-ordered (CO)
metal. We derive a second-order strong-coupling effective Hamiltonian of doped
carriers into the three-fold CO insulator at electron density of , and
then study the - and -wave superconductivities down to by
using the BCS mean-field approximation. It is found that the triplet -wave
pairing is more stable than the -wave one. We also point out that this
coexisting state of the charge ordering and superconductivity is possible to
have critical temperature .Comment: 4 pages, 7 figure
A detailed study of quasinormal frequencies of the Kerr black hole
We compute the quasinormal frequencies of the Kerr black hole using a
continued fraction method. The continued fraction method first proposed by
Leaver is still the only known method stable and accurate for the numerical
determination of the Kerr quasinormal frequencies. We numerically obtain not
only the slowly but also the rapidly damped quasinormal frequencies and analyze
the peculiar behavior of these frequencies at the Kerr limit. We also calculate
the algebraically special frequency first identified by Chandrasekhar and
confirm that it coincide with the quasinormal frequency only at the
Schwarzschild limit.Comment: REVTEX, 15 pages, 7 eps figure
Kerr black hole quasinormal frequencies
Black-hole quasinormal modes (QNM) have been the subject of much recent
attention, with the hope that these oscillation frequencies may shed some light
on the elusive theory of quantum gravity. We compare numerical results for the
QNM spectrum of the (rotating) Kerr black hole with an {\it exact} formula
Re, which is based on Bohr's correspondence
principle. We find a close agreement between the two. Possible implications of
this result to the area spectrum of quantum black holes are discussed.Comment: 3 pages, 2 figure
Highly damped quasinormal modes of Kerr black holes
Motivated by recent suggestions that highly damped black hole quasinormal
modes (QNM's) may provide a link between classical general relativity and
quantum gravity, we present an extensive computation of highly damped QNM's of
Kerr black holes. We do not limit our attention to gravitational modes, thus
filling some gaps in the existing literature. The frequency of gravitational
modes with l=m=2 tends to \omega_R=2 \Omega, \Omega being the angular velocity
of the black hole horizon. If Hod's conjecture is valid, this asymptotic
behaviour is related to reversible black hole transformations. Other highly
damped modes with m>0 that we computed do not show a similar behaviour. The
real part of modes with l=2 and m<0 seems to asymptotically approach a constant
value \omega_R\simeq -m\varpi, \varpi\simeq 0.12 being (almost) independent of
a. For any perturbing field, trajectories in the complex plane of QNM's with
m=0 show a spiralling behaviour, similar to the one observed for
Reissner-Nordstrom (RN) black holes. Finally, for any perturbing field, the
asymptotic separation in the imaginary part of consecutive modes with m>0 is
given by 2\pi T_H (T_H being the black hole temperature). We conjecture that
for all values of l and m>0 there is an infinity of modes tending to the
critical frequency for superradiance (\omega_R=m) in the extremal limit.
Finally, we study in some detail modes branching off the so--called
``algebraically special frequency'' of Schwarzschild black holes. For the first
time we find numerically that QNM multiplets emerge from the algebraically
special Schwarzschild modes, confirming a recent speculation.Comment: 19 pages, 11 figures. Minor typos corrected. Updated references to
take into account some recent development
Reduction in cardiovascular disease events in patients with type 2 diabetes mellitus treated with a sodium–glucose cotransporter 2 inhibitor versus a dipeptidyl peptidase-4 inhibitor: A real-world retrospective administrative database analysis in Japan
AIMS/INTRODUCTION: To evaluate the benefit of sodium–glucose cotransporter 2 inhibitors (SGLT2i) versus dipeptidyl peptidase-4 inhibitors (DPP4i) in reducing cardiovascular disease (CVD) events in patients with type 2 diabetes mellitus with and without a CVD history.MATERIALS AND METHODS: This retrospective cohort study used Japanese hospital administrative data from the Medical Data Vision database (January 2015 to April 2020). Patients with type 2 diabetes mellitus (n=625,739) who were new users of an SGLT2i (n=57,070; 9.1%) or DPP4i (n=568,669; 90.9%) were included. Outcomes included hospitalization for heart failure (hHF), all-cause death (ACD) and the composite of hHF or ACD. Hazard ratios (HR) were calculated using the inverse probability weighting Cox proportional hazards model to compare CVD event risks between treatment groups.RESULTS: Compared with DPP4i, SGLT2i was associated with a significant reduction in hHF risk among patients without a CVD history (HR 0.507, 95% confidence interval 0.283–0.907), but not in the full cohort or those with a CVD history. SGLT2i was associated with a significant risk reduction of ACD (HR 0.592, 95% confidence interval 0.481–0.729) and the composite of hHF or ACD (HR 0.712, 95% confidence interval 0.613–0.826), compared with DPP4i in the full cohort; similar results were observed among patients with and without a CVD history.CONCLUSION: In this real-world study, SGLT2i versus DPP4i was associated with a significant reduction in hHF, ACD and hHF or ACD events in patients with type 2 diabetes mellitus without a CVD history
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