3,854 research outputs found
Comments on Two-Loop Four-Particle Amplitude in Superstring Theory
It is shown that the four-particle amplitude of superstring theory at two
loops obtained in [1,2] is equivalent to the previously obtained results in
[3,4,5]. Here the symmetry in hyperelliptic Riemann surface plays
an important role in the proof.Comment: 10 pages, Latex fil
Two-Loop Superstrings in Hyperelliptic Language III: the Four-Particle Amplitude
We compute explicitly the four-particle amplitude in superstring theories by
using the hyperelliptic language and the newly obtained chiral measure of
D'Hoker and Phong. Although the algebra of the intermediate steps is a little
bit involved, we obtain a quite simple expression for the four-particle
amplitude. As expected, the integrand is independent of all the insertion
points. As an application of the obtained result, we show that the perturbative
correction to the term in type II superstring theories is vanishing
point-wise in (even) moduli space at two loops.Comment: v1, LaTex file, 33 pages; v2, 34 pages, add references and minor
correction
Topological Spin Texture in a Quantum Anomalous Hall Insulator
The quantum anomalous Hall (QAH) effect has been recently discovered in
experiment using thin-film topological insulator with ferromagnetic ordering
and strong spin-orbit coupling. Here we investigate the spin degree of freedom
of a QAH insulator and uncover a fundamental phenomenon that the edge states
exhibit topologically stable spin texture in the boundary when a chiral-like
symmetry is present. This result shows that edge states are chiral in both the
orbital and spin degrees of freedom, and the chiral edge spin texture
corresponds to the bulk topological states of the QAH insulator. We also study
the potential applications of the edge spin texture in designing
topological-state-based spin devices which might be applicable to future
spintronic technologies.Comment: 5 pages manuscript, 8+ pages supplementary information, 8 figures;
published versio
Testing Cosmological Models with Type Ic Super Luminous Supernovae
The use of type Ic Super Luminous Supernovae (SLSN Ic) to examine the
cosmological expansion introduces a new standard ruler with which to test
theoretical models. The sample suitable for this kind of work now includes 11
SLSNe Ic, which have thus far been used solely in tests involving CDM.
In this paper, we broaden the base of support for this new, important cosmic
probe by using these observations to carry out a one-on-one comparison between
the and CDM cosmologies. We individually optimize the
parameters in each cosmological model by minimizing the statistic.
We also carry out Monte Carlo simulations based on these current SLSN Ic
measurements to estimate how large the sample would have to be in order to rule
out either model at a confidence level. The currently available
sample indicates a likelihood of that the
Universe is the correct cosmology versus for the standard
model. These results are suggestive, though not yet compelling, given the
current limited number of SLSNe Ic. We find that if the real cosmology is
CDM, a sample of SLSNe Ic would be sufficient to rule out
at this level of confidence, while SLSNe Ic would be
required to rule out CDM if the real Universe is instead . This difference in required sample size reflects the greater number of
free parameters available to fit the data with CDM. If such SLSNe Ic
are commonly detected in the future, they could be a powerful tool for
constraining the dark-energy equation of state in CDM, and
differentiating between this model and the Universe.Comment: 33 pages, 9 figures, 1 table. Accepted for publication in AJ. arXiv
admin note: text overlap with arXiv:1405.2388, arXiv:1410.0875; text overlap
with arXiv:1409.4429 by other author
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