5,636 research outputs found
Renormalization of transition matrix elements of particle number operators due to strong electron correlation
Renormalization of non-magnetic and magnetic impurities due to electron
double occupancy prohibition is derived analytically by an improved Gutzwiller
approximation. Non-magnetic impurities are effectively weakened by the same
renormalization factor as that for the hopping amplitude, whereas magnetic
impurities are strengthened by the square root of the spin-exchange
renormalization factor, in contrast to results by the conventional Gutzwiller
approximation. We demonstrate it by showing that transition matrix elements of
number operators between assumed excited states and between an assumed ground
state and excited states are renormalized differently than diagonal matrix
elements. Deviation from such simple renormalization with a factor is also
discussed. In addition, as related calculation, we correct an error in
treatment of renormalization of charge interaction in the literature. Namely,
terms from the second order of the transition matrix elements are strongly
suppressed. Since all these results do not depend on the signs of impurity
potential or charge interaction parameter, they are valid both in attractive
and repulsive cases.Comment: 12 page
Isentropic thermodynamics in the PNJL model
We discuss the isentropic trajectories on the QCD phase diagram in the
temperature and the quark chemical potential plane using the
Nambu--Jona-Lasinio model with the Polyakov loop coupling (PNJL model). We
impose a constraint on the strange quark chemical potential so that the strange
quark density is zero, which is the case in the ultra relativistic heavy-ion
collisions. We compare our numerical results with the truncated estimates by
the Taylor expansion in terms of the chemical potential to quantify the
reliability of the expansion used in the lattice QCD simulation. We finally
discuss the strange quark chemical potential induced by the strangeness
neutrality condition and relate it to the ratio of the Polyakov loop and the
anti-Polyakov loop.Comment: 9 pages, 9 figure
Mechanics of the turbulent/non-turbulent interface of a jet
We report the results of an experimental investigation of the mechanics and transport processes at the bounding interface between the turbulent and nonturbulent regions of flow in a turbulent jet, which shows the existence of a finite jump in the tangential velocity at the interface. This is associated with small-scale eddying motion at the outward propagating interface (nibbling) by which irrotational fluid becomes turbulent, and this implies that large-scale engulfment is not the dominant entrainment process. Interpretation of the jump as a singular structure yields an essential and significant contribution to the mean shear in the jet mixing region. Finally, our observations provide a justification for Prandtl’s original hypothesis of a constant eddy viscosity in the nonturbulent outer jet region
Hybrid stars in the light of the massive pulsar PSR J1614-2230
We perform a systematic study of hybrid star configurations using several
parametrizations of a relativistic mean-field hadronic EoS and the NJL model
for three-flavor quark matter. For the hadronic phase we use the stiff GM1 and
TM1 parametrizations, as well as the very stiff NL3 model. In the NJL
Lagrangian we include scalar, vector and 't Hooft interactions. The vector
coupling constant is treated as a free parameter. We also consider that
there is a split between the deconfinement and the chiral phase transitions
which is controlled by changing the conventional value of the vacuum pressure
in the NJL thermodynamic potential by , being a free parameter. We find that, as we
increase the value of , hybrid stars have a larger maximum
mass but are less stable, i.e. hybrid configurations are stable within a
smaller range of central densities. For large enough , stable
hybrid configurations are not possible at all. The effect of increasing the
coupling constant is very similar. We show that stable hybrid
configurations with a maximum mass larger than the observed mass of the pulsar
PSR J1614-2230 are possible for a large region of the parameter space of
and provided the hadronic equation of state contains nucleons
only. When the baryon octet is included in the hadronic phase, only a very
small region of the parameter space allows to explain the mass of PSR
J1614-2230. We compare our results with previous calculations of hybrid stars
within the NJL model. We show that it is possible to obtain stable hybrid
configurations also in the case that corresponds to the
conventional NJL model for which the pressure and density vanish at zero
temperature and chemical potential.Comment: 7 pages, 5 figures; typos in Table 1 have been correcte
Color superconducting matter in a magnetic field
We investigate the effect of a magnetic field on cold dense three-flavor
quark matter using an effective model with four-Fermi interactions with
electric and color neutrality taken into account. The gap parameters Delta_1,
Delta_2, and Delta_3 representing respectively the predominant pairing between
down and strange (d-s) quarks, strange and up (s-u) quarks, and up and down
(u-d) quarks, show the de Haas-van Alphen effect, i.e. oscillatory behavior as
a function of the modified magnetic field B that can penetrate the color
superconducting medium. Without applying electric and color neutrality we find
Delta_2 \approx Delta_3 >> Delta_1 for 2 e B / mu_q^2, where e is the modified
electromagnetic coupling constant and mu_q is one third of the baryon chemical
potential. Because the average Fermi surface for each pairing is affected by
taking into account neutrality, the gap structure changes drastically in this
case; we find Delta_1 >> Delta_2 \approx Delta_3 for 2 e B > mu_q^2. We point
out that the magnetic fields as strong as presumably existing inside magnetars
might induce significant deviations from the gap structure Delta_1 \approx
Delta_2 \approx Delta_3 at zero magnetic field.Comment: 5 pages, 3 figure
Effective Model Approach to the Dense State of QCD Matter
The first-principle approach to the dense state of QCD matter, i.e. the
lattice-QCD simulation at finite baryon density, is not under theoretical
control for the moment. The effective model study based on QCD symmetries is a
practical alternative. However the model parameters that are fixed by hadronic
properties in the vacuum may have unknown dependence on the baryon chemical
potential. We propose a new prescription to constrain the effective model
parameters by the matching condition with the thermal Statistical Model. In the
transitional region where thermal quantities blow up in the Statistical Model,
deconfined quarks and gluons should smoothly take over the relevant degrees of
freedom from hadrons and resonances. We use the Polyakov-loop coupled
Nambu--Jona-Lasinio (PNJL) model as an effective description in the quark side
and show how the matching condition is satisfied by a simple ansatz on the
Polyakov loop potential. Our results favor a phase diagram with the chiral
phase transition located at slightly higher temperature than deconfinement
which stays close to the chemical freeze-out points.Comment: 8 pages, 4 figures; Talk at International Workshop on High Density
Nuclear Matter, Cape Town, South Africa, April 6-9, 201
Views of the Chiral Magnetic Effect
My personal views of the Chiral Magnetic Effect are presented, which starts
with a story about how we came up with the electric-current formula and
continues to unsettled subtleties in the formula. There are desirable features
in the formula of the Chiral Magnetic Effect but some considerations would lead
us to even more questions than elucidations. The interpretation of the produced
current is indeed very non-trivial and it involves a lot of confusions that
have not been resolved.Comment: 19 pages, no figure; typos corrected, references significantly
updated, to appear in Lect. Notes Phys. "Strongly interacting matter in
magnetic fields" (Springer), edited by D. Kharzeev, K. Landsteiner, A.
Schmitt, H.-U. Ye
Are You Tampering With My Data?
We propose a novel approach towards adversarial attacks on neural networks
(NN), focusing on tampering the data used for training instead of generating
attacks on trained models. Our network-agnostic method creates a backdoor
during training which can be exploited at test time to force a neural network
to exhibit abnormal behaviour. We demonstrate on two widely used datasets
(CIFAR-10 and SVHN) that a universal modification of just one pixel per image
for all the images of a class in the training set is enough to corrupt the
training procedure of several state-of-the-art deep neural networks causing the
networks to misclassify any images to which the modification is applied. Our
aim is to bring to the attention of the machine learning community, the
possibility that even learning-based methods that are personally trained on
public datasets can be subject to attacks by a skillful adversary.Comment: 18 page
Light emission patterns from stadium-shaped semiconductor microcavity lasers
We study light emission patterns from stadium-shaped semiconductor (GaAs)
microcavity lasers theoretically and experimentally. Performing systematic wave
calculations for passive cavity modes, we demonstrate that the averaging by
low-loss modes, such as those realized in multi-mode lasing, generates an
emission pattern in good agreement with the ray model's prediction. In
addition, we show that the dependence of experimental far-field emission
patterns on the aspect ratio of the stadium cavity is well reproduced by the
ray model.Comment: 5 pages, 4 figure
Dynamics and Control of a Quasi-1D Spin System
We study experimentally a system comprised of linear chains of spin-1/2
nuclei that provides a test-bed for multi-body dynamics and quantum information
processing. This system is a paradigm for a new class of quantum information
devices that can perform particular tasks even without universal control of the
whole quantum system. We investigate the extent of control achievable on the
system with current experimental apparatus and methods to gain information on
the system state, when full tomography is not possible and in any case highly
inefficient
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