180 research outputs found
Extremal Bundles on Calabi-Yau Threefolds
We study constructions of stable holomorphic vector bundles on Calabi–Yau threefolds, especially those with exact anomaly cancellation which we call extremal. By going through the known databases we find that such examples are rare in general and can be ruled out for the spectral cover construction for all elliptic threefolds. We then introduce a general Hartshorne–Serre construction and use it to find extremal bundles of general ranks and study their stability, as well as computing their Chern numbers. Based on both existing and our new constructions, we revisit the DRY conjecture for the existence of stable sheaves on Calabi–threefolds, and provide theoretical and numerical evidence for its correctness. Our construction can be easily generalized to bundles with no extremal conditions imposed
Experimental NMR Realization of A Generalized Quantum Search Algorithm
A generalized quantum search algorithm, where phase inversions for the marked
state and the prepared state are replaced by phase rotations, is
realized in a 2-qubit NMR heteronuclear system. The quantum algorithm searches
a marked state with a smaller step compared to standard Grover algorithm. Phase
matching requirement in quantum searching is demonstrated by comparing it with
another generalized algorithm where the two phase rotations are and
respectively. Pulse sequences which include non 90 degree pulses are
given.Comment: 12 pages, 2 figures, accepted for publication in Plysics Letters
Temperature-dependence of spin-polarized transport in ferromagnet / unconventional superconductor junctions
Tunneling conductance in ferromagnet / unconventional superconductor
junctions is studied theoretically as a function of temperatures and
spin-polarization in feromagnets. In d-wave superconductor junctions, the
existence of a zero-energy Andreev bound state drastically affects the
temperature-dependence of the zero-bias conductance (ZBC). In p-wave triplet
superconductor junctions, numerical results show a wide variety in
temperature-dependence of the ZBC depending on the direction of the magnetic
moment in ferromagnets and the pairing symmetry in superconductors such as
, and -wave pair potential. The last one is a
promising symmetry of SrRuO. From these characteristic features in the
conductance, we may obtain the information about the degree of
spin-polarization in ferromagnets and the direction of the -vector in
triplet superconductors
Partonic flow and -meson production in Au+Au collisions at = 200 GeV
We present first measurements of the -meson elliptic flow
() and high statistics distributions for different
centralities from = 200 GeV Au+Au collisions at RHIC. In
minimum bias collisions the of the meson is consistent with the
trend observed for mesons. The ratio of the yields of the to those of
the as a function of transverse momentum is consistent with a model
based on the recombination of thermal quarks up to GeV/,
but disagrees at higher momenta. The nuclear modification factor () of
follows the trend observed in the mesons rather than in
baryons, supporting baryon-meson scaling. Since -mesons are
made via coalescence of seemingly thermalized quarks in central Au+Au
collisions, the observations imply hot and dense matter with partonic
collectivity has been formed at RHIC.Comment: 6 pages, 4 figures, submit to PR
Plasma Wakefield Acceleration with a Modulated Proton Bunch
The plasma wakefield amplitudes which could be achieved via the modulation of
a long proton bunch are investigated. We find that in the limit of long bunches
compared to the plasma wavelength, the strength of the accelerating fields is
directly proportional to the number of particles in the drive bunch and
inversely proportional to the square of the transverse bunch size. The scaling
laws were tested and verified in detailed simulations using parameters of
existing proton accelerators, and large electric fields were achieved, reaching
1 GV/m for LHC bunches. Energy gains for test electrons beyond 6 TeV were found
in this case.Comment: 9 pages, 7 figure
The energy dependence of angular correlations inferred from mean- fluctuation scale dependence in heavy ion collisions at the SPS and RHIC
We present the first study of the energy dependence of angular
correlations inferred from event-wise mean transverse momentum
fluctuations in heavy ion collisions. We compare our large-acceptance
measurements at CM energies $\sqrt{s_{NN}} =$ 19.6, 62.4, 130 and 200 GeV to
SPS measurements at 12.3 and 17.3 GeV. $p_t$ angular correlation structure
suggests that the principal source of $p_t$ correlations and fluctuations is
minijets (minimum-bias parton fragments). We observe a dramatic increase in
correlations and fluctuations from SPS to RHIC energies, increasing linearly
with $\ln \sqrt{s_{NN}}$ from the onset of observable jet-related
fluctuations near 10 GeV.Comment: 10 pages, 4 figure
Measurement of Transverse Single-Spin Asymmetries for Di-Jet Production in Proton-Proton Collisions at GeV
We report the first measurement of the opening angle distribution between
pairs of jets produced in high-energy collisions of transversely polarized
protons. The measurement probes (Sivers) correlations between the transverse
spin orientation of a proton and the transverse momentum directions of its
partons. With both beams polarized, the wide pseudorapidity () coverage for jets permits separation of Sivers functions for the valence
and sea regions. The resulting asymmetries are all consistent with zero and
considerably smaller than Sivers effects observed in semi-inclusive deep
inelastic scattering (SIDIS). We discuss theoretical attempts to reconcile the
new results with the sizable transverse spin effects seen in SIDIS and forward
hadron production in pp collisions.Comment: 6 pages total, 1 Latex file, 3 PS files with figure
Longitudinal Double-Spin Asymmetry and Cross Section for Inclusive Jet Production in Polarized Proton Collisions at √s = 200 GeV
We report a measurement of the longitudinal double-spin asymmetry ALL and the differential cross section for inclusive midrapidity jet production in polarized proton collisions at √s=200 GeV. The cross section data cover transverse momenta
- …