6,341 research outputs found
Critical Dynamical Exponent of the Two-Dimensional Scalar Model with Local Moves
We study the scalar one-component two-dimensional (2D) model by
computer simulations, with local Metropolis moves. The equilibrium exponents of
this model are well-established, e.g. for the 2D model
and . The model has also been conjectured to belong to the Ising
universality class. However, the value of the critical dynamical exponent
is not settled. In this paper, we obtain for the 2D model using
two independent methods: (a) by calculating the relative terminal exponential
decay time for the correlation function ,
and thereafter fitting the data as , where is the system
size, and (b) by measuring the anomalous diffusion exponent for the order
parameter, viz., the mean-square displacement (MSD) as , and from the numerically
obtained value , we calculate . For different values of the
coupling constant , we report that and
for the two methods respectively. Our results indicate that
is independent of , and is likely identical to that for the 2D
Ising model. Additionally, we demonstrate that the Generalised Langevin
Equation (GLE) formulation with a memory kernel, identical to those applicable
for the Ising model and polymeric systems, consistently capture the observed
anomalous diffusion behavior.Comment: 14 pages, 4 figures, 6 figure files, to appear in Phys. Rev.
Transverse momentum broadening of vector boson production in high energy nuclear collisions
We calculate in perturbative QCD the transverse momentum broadening of vector
boson production in high energy nuclear collisions. We evaluate the effect of
initial-state parton multiple scattering for the production of the Drell-Yan
virtual photon and bosons. We calculate both the initial- and final-state
multiple scattering effect for the production of heavy quarkonia and their
transverse momentum broadening in both NRQCD and Color Evaporation model of
quarkonium formation. We find that J/ and broadening in
hadron-nucleus collision is close to times the corresponding
Drell-Yan broadening, which gives a good description of existing Fermilab data.
Our calculations are also consistent with RHIC data on J/ broadening in
relativistic heavy ion collisions. We predict the transverse momentum
broadening of vector boson (J/, , and ) production in
relativistic heavy ion collisions at the LHC, and discuss the role of the
vector boson broadening in diagnosing medium properties.Comment: 22 pages, 10 figures, revised version to appear in Phys. Rev.
Quantum Correction in Exact Quantization Rules
An exact quantization rule for the Schr\"{o}dinger equation is presented. In
the exact quantization rule, in addition to , there is an integral term,
called the quantum correction. For the exactly solvable systems we find that
the quantum correction is an invariant, independent of the number of nodes in
the wave function. In those systems, the energy levels of all the bound states
can be easily calculated from the exact quantization rule and the solution for
the ground state, which can be obtained by solving the Riccati equation. With
this new method, we re-calculate the energy levels for the one-dimensional
systems with a finite square well, with the Morse potential, with the symmetric
and asymmetric Rosen-Morse potentials, and with the first and the second
P\"{o}schl-Teller potentials, for the harmonic oscillators both in one
dimension and in three dimensions, and for the hydrogen atom.Comment: 10 pages, no figure, Revte
Low-mass lepton pair production at large transverse momentum
We study the transverse momentum distribution of low-mass lepton pairs
produced in hadronic scattering, using the perturbative QCD factorization
approach. We argue that the distribution at large transverse momentum, , with the pair's invariant mass as low as , can be systematically factorized into universal
parton-to-lepton pair fragmentation functions, parton distributions, and
perturbatively calculable partonic hard parts evaluated at a short distance
scale . We introduce a model for the input lepton pair
fragmentation functions at a scale GeV, which are then evolved
perturbatively to scales relevant at RHIC. Using the evolved fragmentation
functions, we calculate the transverse momentum distributions in hadron-hadron,
hadron-nucleus, and nucleus-nucleus collisions at RHIC. We also discuss the
sensitivity of the transverse momentum distribution of low-mass lepton pairs to
the gluon distribution.Comment: 16 pages, 11 figures, revised version to appear in Phys. Rev.
Electric Field Effect in Multilayer Cr2Ge2Te6: a Ferromagnetic Two-Dimensional Material
The emergence of two-dimensional (2D) materials has attracted a great deal of
attention due to their fascinating physical properties and potential
applications for future nanoelectronic devices. Since the first isolation of
graphene, a Dirac material, a large family of new functional 2D materials have
been discovered and characterized, including insulating 2D boron nitride,
semiconducting 2D transition metal dichalcogenides and black phosphorus, and
superconducting 2D bismuth strontium calcium copper oxide, molybdenum
disulphide and niobium selenide, etc. Here, we report the identification of
ferromagnetic thin flakes of Cr2Ge2Te6 (CGT) with thickness down to a few
nanometers, which provides a very important piece to the van der Waals
structures consisting of various 2D materials. We further demonstrate the giant
modulation of the channel resistance of 2D CGT devices via electric field
effect. Our results illustrate the gate voltage tunability of 2D CGT and the
potential of CGT, a ferromagnetic 2D material, as a new functional quantum
material for applications in future nanoelectronics and spintronics.Comment: To appear in 2D Material
Harnessing high-dimensional hyperentanglement through a biphoton frequency comb
Quantum entanglement is a fundamental resource for secure information
processing and communications, where hyperentanglement or high-dimensional
entanglement has been separately proposed towards high data capacity and error
resilience. The continuous-variable nature of the energy-time entanglement
makes it an ideal candidate for efficient high-dimensional coding with minimal
limitations. Here we demonstrate the first simultaneous high-dimensional
hyperentanglement using a biphoton frequency comb to harness the full potential
in both energy and time domain. The long-postulated Hong-Ou-Mandel quantum
revival is exhibited, with up to 19 time-bins, 96.5% visibilities. We further
witness the high-dimensional energy-time entanglement through Franson revivals,
which is observed periodically at integer time-bins, with 97.8% visibility.
This qudit state is observed to simultaneously violate the generalized Bell
inequality by up to 10.95 deviations while observing recurrent
Clauser-Horne-Shimony-Holt S-parameters up to 2.76. Our biphoton frequency comb
provides a platform in photon-efficient quantum communications towards the
ultimate channel capacity through energy-time-polarization high-dimensional
encoding
Accessing tri-gluon correlations in the nucleon via the single spin asymmetry in open charm production
We calculate the single transverse-spin asymmetry for open charm production
in collisions within the QCD collinear factorization approach. We include
contributions from both twist-three quark-gluon and tri-gluon correlation
functions. We find that the quark-gluon correlation functions alone generate
only a very small asymmetry for open charm production in the kinematic region
of current interest at RHIC, so that the observation of any significant
single-spin asymmetry would be a clear indication of the presence of tri-gluon
correlations inside a polarized proton. We furthermore demonstrate that the
tri-gluon contribution could be very different for the production of and
mesons. These features make the single spin asymmetry in open charm
production in polarized collisions at RHIC an excellent probe of tri-gluon
correlation functions.Comment: 10 pages, 7 figure
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