20,757 research outputs found
Topology and Strings: Topics in
A review on topological strings and the geometry of the space of two
dimensional theories. (Lectures given by C. Gomez at the Enrico Fermi Summer
School, Varenna, July 1994)Comment: 61 pages, late
A Note on the String Analog of Super-Symmetric Yang-Mills
A connection between the conifold locus of the type II string on the
Calabi-Yau manifold and the geometry of the quantum moduli of
super Yang-Mills is presented. This relation is obtained from
the anomalous behaviour of the super Yang-Mills special coordinates
under -duality transformation in .Comment: 7 pages, Late
The homotopy type of the topological cobordism category
We define a cobordism category of topological manifolds and prove that if its classifying space is weakly equivalent to , where is the Thom spectrum of the inverse of the
canonical bundle over . We also give versions with tangential
structures and boundary. The proof uses smoothing theory and excision in the
tangential structure to reduce the statement to the computation of the homotopy
type of smooth cobordism categories due to Galatius-Madsen-Tillman-Weiss.Comment: 61 pages, 9 figures. Minor correction
One-loop Parke-Taylor factors for quadratic propagators from massless scattering equations
In this paper we reconsider the Cachazo-He-Yuan construction (CHY) of the so
called scattering amplitudes at one-loop, in order to obtain quadratic
propagators. In theories with colour ordering the key ingredient is the
redefinition of the Parke-Taylor factors. After classifying all the possible
one-loop CHY-integrands we conjecture a new one-loop amplitude for the massless
Bi-adjoint theory. The prescription directly reproduces the quadratic
propagators from of the traditional Feynman approach.Comment: 43 pages, new appendix added, few typos corrected. Accepted for
publication in JHE
Non-planar one-loop Parke-Taylor factors in the CHY approach for quadratic propagators
In this work we have studied the Kleiss-Kuijf relations for the recently
introduced Parke-Taylor factors at one-loop in the CHY approach, that reproduce
quadratic Feynman propagators. By doing this, we were able to identify the
non-planar one-loop Parke-Taylor factors. In order to check that, in fact,
these new factors can describe non-planar amplitudes, we applied them to the
bi-adjoint theory. As a byproduct, we found a new type of graphs that
we called the non-planar CHY-graphs. These graphs encode all the information
for the subleading order at one-loop, and there is not an equivalent of these
in the Feynman formalism.Comment: 35 pages, typos corrected, references adde
Electromagnetic quasinormal modes of five-dimensional topological black holes
We calculate exactly the QNF of the vector type and scalar type
electromagnetic fields propagating on a family of five-dimensional topological
black holes. To get a discrete spectrum of quasinormal frequencies for the
scalar type electromagnetic field we find that it is necessary to change the
boundary condition usually imposed at the asymptotic region. Furthermore for
the vector type electromagnetic field we impose the usual boundary condition at
the asymptotic region and we discuss the existence of unstable quasinormal
modes in the five-dimensional topological black holes.Comment: 16 pages. Already published in Revista Mexicana de Fisic
Constraints to the magnetospheric properties of T Tauri stars - II. The Mg II ultraviolet feature
The atmospheric structure of T Tauri Stars (TTSs) and its connection with the
large scale outflow is poorly known. Neither the effect of the magnetically
mediated inter- action between the star and the disc in the stellar atmosphere
is well understood. The Mg II multiplet is a fundamental tracer of TTSs
atmospheres and outflows, and is the strongest feature in the near-ultraviolet
spectrum of TTSs. The International Ultraviolet Explorer and Hubble Space
Telescope data archives provide a unique set to study the main physical
compounds contributing to the line profile and to derive the properties of the
line formation region. The Mg II profiles of 44 TTSs with resolution 13,000 to
30,000 are available in these archives. In this work, we use this data set to
measure the main observables: flux, broadening, asymmetry, terminal velocity of
the outflow, and the velocity of the Discrete Absorption Components. For some
few sources repeated observations are available and variability has been
studied. There is a warm wind that at sub-AU scales absorbs the blue wing of
the Mg II profiles. The main result found in this work is the correlation
between the line broadening, Mg II flux, terminal velocity of the flow and
accretion rate. Both outflow and magnetospheric plasma contribute to the Mg II
flux. The flux-flux correlation between Mg II and C IV or He II is confirmed;
however, no correlation is found between the Mg II flux and the ultraviolet
continuum or the H2 emission.Comment: 21 pages, 20 figure
Constraints to the magnetospheric properties of T Tauri stars. I. The C II], Fe II] and Si II] ultraviolet features
The C II] feature at ~2325 Angstrom is very prominent in the spectra of T
Tauri stars (TTSs). This feature is a quintuplet of semiforbidden transitions
excited at electron temperatures around 10,000 K that, together with the nearby
Si II] and Fe II] features, provides a reliable optically thin tracer for
accurate measurement of the plasma properties in the magnetospheres of TTSs.
The spectra of 20 (out of 27) TTSs observed with the Space Telescope Imaging
Spectrograph (STIS) on board the Hubble Space Telescope (HST) have good enough
signal to noise ratio (S/N) at the C II] wavelength. For these stars we have
determined electron densities (ne) and temperatures (Te) in the line emission
region as well as the profile broadening (sigma). For most of the stars in the
sample (17) we obtain 10^{4.1} < Te < 10^{4.5} K and 10^{8} < ne < 10^{12}
cm^{-3}. These stars have suprathermal line broadening (35 < sigma < 165 km
s^{-1}), except TW Hya and CY Tau with thermal line broadening. Both C II] line
luminosity and broadening are found to correlate with the accretion rate. Line
emission seems to be produced in the magnetospheric accretion flow, close to
the disk. There are three exceptions: DG Tau, RY Tau and FU Ori. The line
centroids are blueshifted indicating that the line emission in these three
stars is dominated by the outflow.Comment: 13 pages, 15 figures, published in MNRAS minor change
- …