282,062 research outputs found
Finite density phase transition of QCD with and using canonical ensemble method
In a progress toward searching for the QCD critical point, we study the
finite density phase transition of and 2 lattice QCD at finite
temperature with the canonical ensemble approach. We develop a winding number
expansion method to accurately project out the particle number from the fermion
determinant which greatly extends the applicable range of baryon number sectors
to make the study feasible. Our lattice simulation was carried out with the
clover fermions and improved gauge action. For a given temperature, we
calculate the baryon chemical potential from the canonical approach to look for
the mixed phase as a signal for the first order phase transition. In the case
of , we observe an "S-shape" structure in the chemical potential-density
plane due to the surface tension of the mixed phase in a finite volume which is
a signal for the first order phase transition. We use the Maxwell construction
to determine the phase boundaries for three temperatures below . The
intersecting point of the two extrapolated boundaries turns out to be at the
expected first order transition point at with . This serves as a
check for our method of identifying the critical point. We also studied the
case, but do not see a signal of the mixed phase for temperature as
low as 0.83 .Comment: 28 pages, 11 figures,references added, final versio
A propeller scenario for the gamma-ray emission of low-mass X-ray binaries: The case of XSS J12270-4859
XSS J12270-4859 is the only low mass X-ray binary (LMXB) with a proposed
persistent gamma-ray counterpart in the Fermi-LAT domain, 2FGL 1227.7-4853.
Here, we present the results of the analysis of recent INTEGRAL observations,
aimed at assessing the long-term variability of the hard X-ray emission, and
thus the stability of the accretion state. We confirm that the source behaves
as a persistent hard X-ray emitter between 2003 and 2012. We propose that XSS
J12270-4859 hosts a neutron star in a propeller state, a state we investigate
in detail, developing a theoretical model to reproduce the associated X-ray and
gamma-ray properties. This model can be understood as being of a more general
nature, representing a viable alternative by which LMXBs can appear as
gamma-ray sources. In particular, this may apply to the case of millisecond
pulsars performing a transition from a state powered by the rotation of their
magnetic field, to a state powered by matter in-fall, such as that recently
observed from the transitional pulsar PSR J1023+0038. While the surface
magnetic field of a typical NS in a LMXB is lower by more than four orders of
magnitude than the much more intense fields of neutron stars accompanying
high-mass binaries, the radius at which the matter in-flow is truncated in a
NS-LMXB system is much lower. The magnetic field at the magnetospheric
interface is then orders of magnitude larger at this interface, and as
consequence, so is the power to accelerate electrons. We demonstrate that the
cooling of the accelerated electron population takes place mainly through
synchrotron interaction with the magnetic field permeating the interface, and
through inverse Compton losses due to the interaction between the electrons and
the synchrotron photons they emit. We found that self-synchrotron Compton
processes can explain the high energy phenomenology of XSS J12270-4859.Comment: 12 pages, 3 figures, accepted for publication in MNRAS. References
update
Pentagonal puckering in a sheet of amorphous graphene
Ordered graphene has been extensively studied. In this paper we undertake a
first density functional study of it topologically disordered analogues of
graphene, in the form of a random network, consisting predominantly of
hexagonal rings, but also including pentagons and heptagons. After some
preliminaries with crystalline material, we relax various random network models
and find that the presence of carbon pentagons induce local curvature, thus
breaking the initial planar symmetry, in some analogy with the case of
fullerenes. Using density functional theory to calculate the total energy, we
find that while the planar state is locally stable, there is a puckered state
that has lower energy. The scale of the puckering is consistent with that
expected with local maxima and minima associated with pentagons surrounded by
larger rings; forming local "buckyball domes"
decays
Effective chiral theory of mesons is applied to study the four decay modes of
. Theoretical values of the branching ratios are in
agreement with the data. The theory predicts that the resonance plays a
dominant role in these decays. There is no new parameter in this study.Comment: 12 pages and one figur
Critical point of QCD from lattice simulations in the canonical ensemble
A canonical ensemble algorithm is employed to study the phase diagram of QCD using lattice simulations. We lock in the desired quark number sector
using an exact Fourier transform of the fermion determinant. We scan the phase
space below and look for an S-shape structure in the chemical potential,
which signals the coexistence phase of a first order phase transition in finite
volume. Applying Maxwell construction, we determine the boundaries of the
coexistence phase at three temperatures and extrapolate them to locate the
critical point. Using an improved gauge action and improved Wilson fermions on
lattices with a spatial extent of 1.8 \fm and quark masses close to that of
the strange, we find the critical point at and baryon
chemical potential .Comment: 5 pages, 7 figures, references added, published versio
Pauli Spin Blockade of Heavy Holes in a Silicon Double Quantum Dot
In this work, we study hole transport in a planar silicon
metal-oxide-semiconductor based double quantum dot. We demonstrate Pauli spin
blockade in the few hole regime and map the spin relaxation induced leakage
current as a function of inter-dot level spacing and magnetic field. With
varied inter-dot tunnel coupling we can identify different dominant spin
relaxation mechanisms. Applying a strong out-of-plane magnetic field causes an
avoided singlet-triplet level crossing, from which the heavy hole g-factor
0.93, and the strength of spin-orbit interaction 110 eV, can
be obtained. The demonstrated strong spin-orbit interaction of heavy hole
promises fast local spin manipulation using only electrical fields, which is of
great interest for quantum information processing.Comment: 15 pages, 4 figure
D^0-D^0bar mixing in \Upsilon(1S) \to D^0 D^0bar decay at Super-B
\Dz-\Dzb mixing and significant CP violation in the charm system may
indicate the signature of new physics. In this study, we suggest that the
coherent \DzDzb events from the decay of \Upsilon(1S) \to \Dz \Dzb can be
used to measure both mixing parameters and CP violation in charm decays. The
neutral mesons from decay are strongly boosted, so that it
will offer the possibility to measure the proper-time interval, ,
between the fully-reconstructed \Dz and \Dzb. Both coherent and
time-dependent information can be used to extract \Dz-\Dzb mixing parameters.
The sensitivity of the measurement should be improved at B factories or
super-B.Comment: 6 pages, 1 figure, this is the last version to appear in Phys. Rev.
Extracting Energy from a Black Hole through Its Disk
When some magnetic field lines connect a Kerr black hole with a disk rotating
around it, energy and angular momentum are transferred between them. If the
black hole rotates faster than the disk, for a thin Keplerian
disk, then energy and angular momentum are extracted from the black hole and
transferred to the disk ( is the mass and is the angular momentum
of the black hole). This way the energy originating in the black hole may be
radiated away by the disk.
The total amount of energy that can be extracted from the black hole spun
down from to by a thin Keplerian disk is
. This is larger than which can be
extracted by the Blandford-Znajek mechanism.Comment: 8 pages, 2 figure
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