12,306 research outputs found
Factorizing twists and R-matrices for representations of the quantum affine algebra U_q(\hat sl_2)
We calculate factorizing twists in evaluation representations of the quantum
affine algebra U_q(\hat sl_2). From the factorizing twists we derive a
representation independent expression of the R-matrices of U_q(\hat sl_2).
Comparing with the corresponding quantities for the Yangian Y(sl_2), it is
shown that the U_q(\hat sl_2) results can be obtained by `replacing numbers by
q-numbers'. Conversely, the limit q -> 1 exists in representations of U_q(\hat
sl_2) and both the factorizing twists and the R-matrices of the Yangian Y(sl_2)
are recovered in this limit.Comment: 19 pages, LaTe
A spin foam model for pure gauge theory coupled to quantum gravity
We propose a spin foam model for pure gauge fields coupled to Riemannian
quantum gravity in four dimensions. The model is formulated for the
triangulation of a four-manifold which is given merely combinatorially. The
Riemannian Barrett--Crane model provides the gravity sector of our model and
dynamically assigns geometric data to the given combinatorial triangulation.
The gauge theory sector is a lattice gauge theory living on the same
triangulation and obtains from the gravity sector the geometric information
which is required to calculate the Yang--Mills action. The model is designed so
that one obtains a continuum approximation of the gauge theory sector at an
effective level, similarly to the continuum limit of lattice gauge theory, when
the typical length scale of gravity is much smaller than the Yang--Mills scale.Comment: 18 pages, LaTeX, 1 figure, v2: details clarified, references adde
Numerical simulations of neutron star-black hole binaries in the near-equal-mass regime
Simulations of neutron star-black hole (NSBH) binaries generally consider
black holes with masses in the range , where we expect to find
most stellar mass black holes. The existence of lower mass black holes,
however, cannot be theoretically ruled out. Low-mass black holes in binary
systems with a neutron star companion could mimic neutron star-neutron (NSNS)
binaries, as they power similar gravitational wave (GW) and electromagnetic
(EM) signals. To understand the differences and similarities between NSNS
mergers and low-mass NSBH mergers, numerical simulations are required. Here, we
perform a set of simulations of low-mass NSBH mergers, including systems
compatible with GW170817. Our simulations use a composition and temperature
dependent equation of state (DD2) and approximate neutrino transport, but no
magnetic fields. We find that low-mass NSBH mergers produce remnant disks
significantly less massive than previously expected, and consistent with the
post-merger outflow mass inferred from GW170817 for moderately asymmetric mass
ratio. The dynamical ejecta produced by systems compatible with GW170817 is
negligible except if the mass ratio and black hole spin are at the edge of the
allowed parameter space. That dynamical ejecta is cold, neutron-rich, and
surprisingly slow for ejecta produced during the tidal disruption of a neutron
star : . We also find that the final mass of the remnant
black hole is consistent with existing analytical predictions, while the final
spin of that black hole is noticeably larger than expected -- up to for our equal mass case
AC Magnetotransport in Reentrant Insulating Phases of Two-dimensional Electrons near 1/5 and 1/3 Landau fillings
We have measured high frequency magnetotransport of a high quality
two-dimensional electron system (2DES) near the reentrant insulating phase
(RIP) at Landau fillings () between 1/5 and 2/9. The
magneto\textit{conductivity} in the RIP has resonant behavior around 150 MHz,
showing a \textit{peak} at 0.21. Our data support the interpretation
of the RIP as due to some pinned electron solid. We have also investigated a
narrowly confined 2DES recently found to have a RIP at 1/31/2 and we
have revealed features, not seen in DC transport, that suggest some intriguing
interplay between the 1/3 FQHE and RIP.Comment: 4 pages and 1 figure (amsart format), 16th International Conference
on High Magnetic Fields in Semiconductor Physics (SemiMag16), August 2-6,
2004, Tallahasse
Formation of a high quality two-dimensional electron gas on cleaved GaAs
We have succeeded in fabricating a two-dimensional electron gas (2DEG) on the cleaved (110) edge of a GaAs wafer by molecular beam epitaxy (MBE). A (100) wafer previously prepared by MBE growth is reinstalled in the MBE chamber so that an in situ cleave exposes a fresh (110) GaAs edge for further MBE overgrowth. A sequence of Si-doped AlGaAs layers completes the modulation-doped structure at the cleaved edge. Mobilities as high as 6.1×10^5 cm^2/V s are measured in the 2DEG at the cleaved interface
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