9 research outputs found
The Global-Normal Disk Oscillations and the Persistent Low Frequency QPO in X-ray Binaries
We suggest that persistent low-frequency quasi-periodic oscillations (QPOs)
detected in X-ray, ultraviolet, optical energy ranges the black hole (BH)
sources XTE J1118+480, GRO J1655-40 LMC X-1 at ~ 0.1 Hz, and QPOs in HZ Her/Her
X-1 at ~ 0.05 Hz and in Neutron Star (NS) binaries 4U 1323-62, 4U 1746-31 and
EXO 0748-76 at ~ 1 Hz are caused by the global disk oscillations in the
direction normal to the disk (normal mode). We argue that these disk
oscillations are a result of the gravitational interaction between the central
compact object and the disk. A small displacement of the disk from the
equatorial plane results in a linear gravitational restoring force opposite to
this displacement. Our analysis shows that the frequency of this mode is a
function of the mass of the central object and it also depends on the inner and
outer radii of the disk which in turn are related to the rotation period of the
binary system. We derive an analytical formula for the frequency of the normal
disk mode and show that these frequencies can be related to the persistent
lower QPO frequencies observed in the NS and BH sources. We offer a new
independent approach to the black hole mass determination by interpreting this
low QPO frequency as the global disk oscillation frequency. The implementation
of this method combined with the independent method which uses the X-ray energy
spectra (Shrader & Titarchuk 1999) results in stringent constraints for the
black hole masses.Comment: 14 pages, 1 figure, to appear in the Astrophysical Journal Letter
Regularity Properties and Pathologies of Position-Space Renormalization-Group Transformations
We reconsider the conceptual foundations of the renormalization-group (RG)
formalism, and prove some rigorous theorems on the regularity properties and
possible pathologies of the RG map. Regarding regularity, we show that the RG
map, defined on a suitable space of interactions (= formal Hamiltonians), is
always single-valued and Lipschitz continuous on its domain of definition. This
rules out a recently proposed scenario for the RG description of first-order
phase transitions. On the pathological side, we make rigorous some arguments of
Griffiths, Pearce and Israel, and prove in several cases that the renormalized
measure is not a Gibbs measure for any reasonable interaction. This means that
the RG map is ill-defined, and that the conventional RG description of
first-order phase transitions is not universally valid. For decimation or
Kadanoff transformations applied to the Ising model in dimension ,
these pathologies occur in a full neighborhood of the low-temperature part of the first-order
phase-transition surface. For block-averaging transformations applied to the
Ising model in dimension , the pathologies occur at low temperatures
for arbitrary magnetic-field strength. Pathologies may also occur in the
critical region for Ising models in dimension . We discuss in detail
the distinction between Gibbsian and non-Gibbsian measures, and give a rather
complete catalogue of the known examples. Finally, we discuss the heuristic and
numerical evidence on RG pathologies in the light of our rigorous theorems.Comment: 273 pages including 14 figures, Postscript, See also
ftp.scri.fsu.edu:hep-lat/papers/9210/9210032.ps.