2,497 research outputs found
Systematic approach to cyclic orbifolds
We introduce an orbifold induction procedure which provides a systematic
construction of cyclic orbifolds, including their twisted sectors. The
procedure gives counterparts in the orbifold theory of all the
current-algebraic constructions of conformal field theory and enables us to
find the orbifold characters and their modular transformation properties.Comment: 39 pages, LaTeX. v2,3: references added. v4: typos correcte
New Spin-Two Gauged Sigma Models and General Conformal Field Theory
Recently, we have studied the general Virasoro construction at one loop in
the background of the general non-linear sigma model. Here, we find the action
formulation of these new conformal field theories when the background sigma
model is itself conformal. In this case, the new conformal field theories are
described by a large class of new spin-two gauged sigma models. As examples of
the new actions, we discuss the spin-two gauged WZW actions, which describe the
conformal field theories of the generic affine-Virasoro construction, and the
spin-two gauged g/h coset constructions. We are able to identify the latter as
the actions of the local Lie h-invariant conformal field theories, a large
class of generically irrational conformal field theories with a local gauge
symmetry.Comment: LaTeX, 28 pages, references and clarifying remarks adde
Cyclic Coset Orbifolds
We apply the new orbifold duality transformations to discuss the special case
of cyclic coset orbifolds in further detail. We focus in particular on the case
of the interacting cyclic coset orbifolds, whose untwisted sectors are
Z_\lambda(permutation)-invariant g/h coset constructions which are not \lambda
copies of coset constructions. Because \lambda copies are not involved, the
action of Z_\lambda(permutation) in the interacting cyclic coset orbifolds can
be quite intricate. The stress tensors and ground state conformal weights of
all the sectors of a large class of these orbifolds are given explicitly and
special emphasis is placed on the twisted h subalgebras which are generated by
the twisted (0,0) operators of these orbifolds. We also discuss the systematics
of twisted (0,0) operators in general coset orbifolds.Comment: 30 page
Imaging X-ray, Optical, and Infrared Observations of the Transient Anomalous X-ray Pulsar XTE J1810-197
We report X-ray imaging, timing, and spectral studies of XTE J1810-197, a
5.54s pulsar discovered by Ibrahim et al. (2003) in recent RXTE observations.
In a set of short exposures with the Chandra HRC camera we detect a strongly
modulated signal (55+/-4% pulsed fraction) with the expected period located at
(J2000) 18:09:51.08, -19:43:51.7, with a uncertainty radius of 0.6 arcsec (90%
C.L.). Spectra obtained with XMM-Newton are well fitted by a two-component
model that typically describes anomalous X-ray pulsars (AXPs), an absorbed
blackbody plus power law with parameters kT = 0.67+/-0.01 keV, Gamma=3.7+/-0.2,
N_H=(1.05+/-0.05)E22 cm^-2, and Fx(0.5-10 keV) = 3.98E-11 ergs/cm2/s.
Alternatively, a 2T blackbody fit is just as acceptable. The location of CXOU
J180951.1-194351 is consistent with a point source seen in archival Einstein,
Rosat, & ASCA images, when its flux was nearly two orders-of-magnitude fainter,
and from which no pulsations are found. The spectrum changed dramatically
between the "quiescent" and "active" states, the former can be modeled as a
softer blackbody. Using XMM timing data, we place an upper limit of 0.03 lt-s
on any orbital motion in the period range 10m-8hr. Optical and infrared images
obtained on the SMARTS 1.3m telescope at CTIO show no object in the Chandra
error circle to limits V=22.5, I=21.3, J=18.9, & K=17.5. Together, these
results argue that CXOU J180951.1-194351 is an isolated neutron star, one most
similar to the transient AXP AX J1844.8-0256. Continuing study of XTE J1810-197
in various states of luminosity is important for understanding and possibly
unifying a growing class of isolated, young neutron stars that are not powered
by rotation.Comment: 12 pages, 7 figures, AAS LaTex, uses emulateapj5.sty. Updated to
include additional archival data and a new HRC observation. To appear in The
Astrophysical Journa
Higher-Derivative Two-Dimensional Massive Fermion Theories
We consider the canonical quantization of a generalized two-dimensional
massive fermion theory containing higher odd-order derivatives. The
requirements of Lorentz invariance, hermiticity of the Hamiltonian and absence
of tachyon excitations suffice to fix the mass term, which contains a
derivative coupling. We show that the basic quantum excitations of a
higher-derivative theory of order 2N+1 consist of a physical usual massive
fermion, quantized with positive metric, plus 2N unphysical massless fermions,
quantized with opposite metrics. The positive metric Hilbert subspace, which is
isomorphic to the space of states of a massive free fermion theory, is selected
by a subsidiary-like condition. Employing the standard bosonization scheme, the
equivalent boson theory is derived. The results obtained are used as a
guideline to discuss the solution of a theory including a current-current
interaction.Comment: 23 pages, Late
PSR J2229+6114: Discovery of an Energetic Young Pulsar in the Error Box of the EGRET Source 3EG J2227+6122
We report the detection of radio and X-ray pulsations at a period of 51.6 ms
from the X-ray source RX/AX J2229.0+6114 in the error box of the EGRET source
3EG J2227+6122. An ephemeris derived from a single ASCA observation and
multiple epochs at 1412 MHz from Jodrell Bank indicates steady spin-down with
P-dot = 7.83 x 10^(-14) s/s. From the measured P and P-dot we derive spin-down
power E-dot = 2.2 x 10^(37) erg/s, magnetic field B = 2.0 x 10^(12) G, and
characteristic age P/2P-dot = 10,460 yr. An image from the Chandra X-ray
Observatory reveals a point source surrounded by centrally peaked diffuse
emission that is contained within an incomplete radio shell. We assign the name
G106.6+2.9 to this new supernova remnant, which is evidently a pulsar wind
nebula. For a distance of 3 kpc estimated from X-ray absorption, the ratio of
X-ray luminosity to spin-down power is ~8 x 10^(-5), smaller than that of most
pulsars, but similar to the Vela pulsar. If PSR J2229+6114 is the counterpart
of 3EG J2227+6122 then its efficiency of gamma-ray production, if isotropic, is
0.016 (d/3 kpc)^2. It obeys an established trend of gamma-ray efficiency among
known gamma-ray pulsars which, in combination with the demonstrated absence of
any other plausible counterpart for 3EG J2227+6122, makes the identification
compelling. If confirmed, this identification bolsters the pulsar model for
unidentified Galactic EGRET sources.Comment: 5 pages, 4 figures, accepted by The Astrophysical Journal Letter
Canonical Transformations in a Higher-Derivative Field Theory
It has been suggested that the chiral symmetry can be implemented only in
classical Lagrangians containing higher covariant derivatives of odd order.
Contrary to this belief, it is shown that one can construct an exactly soluble
two-dimensional higher-derivative fermionic quantum field theory containing
only derivatives of even order whose classical Lagrangian exhibits chiral-gauge
invariance. The original field solution is expressed in terms of usual Dirac
spinors through a canonical transformation, whose generating function allows
the determination of the new Hamiltonian. It is emphasized that the original
and transformed Hamiltonians are different because the mapping from the old to
the new canonical variables depends explicitly on time. The violation of
cluster decomposition is discussed and the general Wightman functions
satisfying the positive-definiteness condition are obtained.Comment: 12 pages, LaTe
Trust in Crowds: probabilistic behaviour in anonymity protocols
The existing analysis of the Crowds anonymity protocol assumes that a participating member is either âhonestâ or âcorruptedâ. This paper generalises this analysis so that each member is assumed to maliciously disclose the identity of other nodes with a probability determined by her vulnerability to corruption. Within this model, the trust in a principal is defined to be the probability that she behaves honestly. We investigate the effect of such a probabilistic behaviour on the anonymity of the principals participating in the protocol, and formulate the necessary conditions to achieve âprobable innocenceâ. Using these conditions, we propose a generalised Crowds-Trust protocol which uses trust information to achieves âprobable innocenceâ for principals exhibiting probabilistic behaviour
Quantum nature of cyclotron harmonics in thermal spectra of neutron stars
Some isolated neutron stars show harmonically spaced absorption features in
their thermal soft X-ray spectra. The interpretation of the features as a
cyclotron line and its harmonics has been suggested, but the usual explanation
of the harmonics as caused by relativistic effects fails because the
relativistic corrections are extremely small in this case. We suggest that the
features correspond to the peaks in the energy dependence of the free-free
opacity in a quantizing magnetic field, known as quantum oscillations. The
peaks arise when the transitions to new Landau levels become allowed with
increasing the photon energy; they are strongly enhanced by the square-root
singularities in the phase-space density of quantum states in the case when the
free (non-quantized) motion is effectively one-dimensional. To explore
observable properties of these quantum oscillations, we calculate models of
hydrogen neutron star atmospheres with B \sim 10^{10} - 10^{11} G (i.e.,
electron cyclotron energy E_{c,e} = 0.1 - 1 keV) and T_{eff} = 1 - 3 MK. Such
conditions are thought to be typical for the so-called central compact objects
in supernova remnants, such as 1E 1207.4-5209 in PKS 1209-51/52. We show that
observable features at the electron cyclotron harmonics form at moderately
large values of the quantization parameter, b_{eff} = E_{c,e}/kT_{eff} = 0.5 -
20. The equivalent widths of the features can reach 100 - 200 eV; they grow
with increasing b_{eff} and are lower for higher harmonics.Comment: 6 pages; shortened, references updated; published in Ap
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