328,618 research outputs found
Black hole evaporation based upon a q-deformation description
A toy model based upon the -deformation description for studying the
radiation spectrum of black hole is proposed. The starting point is to make an
attempt to consider the spacetime noncommutativity in the vicinity of black
hole horizon. We use a trick that all the spacetime noncommutative effects are
ascribed to the modification of the behavior of the radiation field of black
hole and a kind of q-deformed degrees of freedom are postulated to mimic the
radiation particles that live on the noncommutative spacetime, meanwhile the
background metric is preserved as usual. We calculate the radiation spectrum of
Schwarzschild black hole in this framework. The new distribution deviates from
the standard thermal spectrum evidently. The result indicates that some
correlation effect will be introduced to the system if the noncommutativity is
taken into account. In addition, an infrared cut-off of the spectrum is the
prediction of the model.Comment: 13 pages, 2 figure
A note on the Lee-Yang singularity coupled to 2d quantum gravity
We show how to obtain the critical exponent of magnetization in the Lee-Yang
edge singularity model coupled to two-dimensional quantum gravity
RKKY Interactions in Graphene Landau Levels
We study RKKY interactions for magnetic impurities on graphene in situations
where the electronic spectrum is in the form of Landau levels. Two such
situations are considered: non-uniformly strained graphene, and graphene in a
real magnetic field. RKKY interactions are enhanced by the lowest Landau level,
which is shown to form electron states binding with the spin impurities and add
a strong non-perturbative contribution to pairwise impurity spin interactions
when their separation no more than the magnetic length. Beyond this
interactions are found to fall off as due to perturbative effects of
the negative energy Landau levels. Based on these results, we develop simple
mean-field theories for both systems, taking into account the fact that
typically the density of states in the lowest Landau level is much smaller than
the density of spin impurities. For the strain field case, we find that the
system is formally ferrimagnetic, but with very small net moment due to the
relatively low density of impurities binding electrons. The transition
temperature is nevertheless enhanced by them. For real fields, the system forms
a canted antiferromagnet if the field is not so strong as to pin the impurity
spins along the field. The possibility that the system in this latter case
supports a Kosterlitz-Thouless transition is discussed
Multiwavelength Observations of the BL Lacertae Object PKS 2155-304 with XMM-Newton
The optical-UV and X-ray instruments on-board XMM-Ndewton provide an
excellent opportunity to perform simultaneous observations of violently
variable objects over a broad wavelength range. The UV and X-ray bright BL Lac
object PKS 2155-304 has been repeatedly observed with XMM-Ndewton about twice
per year. In this paper, we present a detailed analysis of the simultaneous
multiwavelength variability of the source from optical to X-rays, based on the
currently available XMM-Ndewton observations. These observations probed the
intra-day multiwavelength variability at optical-UV and X-ray wavelengths of
the source. The UV variability amplitude is substantially smaller than the
X-ray one, and the hardness ratios of the UV to X-rays correlates with the
X-ray fluxes: the brighter the source, the flatter the UV-X-ray spectra. On
2000 May 30-31 the UV and X-ray light curves were weakly correlated, while the
UV variations followed the X-ray ones with no detectable lags on 2000 November
19-21. On 2001 November 30 the source exhibited a major X-ray flare that was
not detected in the optical. The intra-day UV and X-ray variability presented
here is not similar to the inter-day UV and X-ray variability obtained from the
previous coordinated extensive multiwavelength campaigns on the source,
indicating that different ``modes'' of variability might be operating in PKS
2155-304 on different timescales or from epoch to epoch.Comment: Accepted by Ap
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