129 research outputs found
A Note on AdS/CFT Dual of SL(2,Z) Action on 3D Conformal Field Theories with U(1) Symmetry
In this letter, we elaborate on the SL(2,Z) action on three dimensional
conformal field theories with U(1) symmetry introduced by Witten, by trying to
give an explicit verification of the claim regarding holographic dual of the S
operation in AdS/CFT correspondence. A consistency check with the recently
proposed prescription on boundary condition of bulk fields when we deform the
boundary CFT in a non-standard manner is also discussed.Comment: LaTex, 1+15 pages, 1 figure, v2: discussion in terms of deformation
theory is adde
Flows and polarization of early photons with magnetic field at strong coupling
Recent experimental results from RHIC and LHC on hard photon emission rates
in heavy-ion collisions indicate a large azimuthal asymmetry of photon emission
rate parameterized by the elliptic flow v_2. Motivated by a recent proposal
that the early magnetic field created by two colliding heavy-ions may be
responsible for this large azimuthal asymmetry of photon emission rate, we
compute the azimuthal dependence of the photon emission rate from a strongly
coupled finite temperature plasma with magnetic field in the framework of
gauge/gravity correspondence. We also propose and compute a new observable,
"in/out-plane polarization asymmetry", constructed from the polarization
dependence of the photon emission rates. We observe that both the azimuthal and
polarization asymmetry of photon emissions are strongly affected by the
triangle anomaly (chiral anomaly) for low frequency regime below 1 GeV.Comment: 25 pages, 7 figure
Recent Theoretical Developments in Strongly Coupled QCD
Heavy-ion collisions involve strongly coupled dynamics of QCD in the entire
history of time evolution. We review recent theoretical efforts to meet this
challenge, focusing on the two approaches that the speaker has contributed to:
1) Holography or AdS/CFT correspondence, and 2) Symmetry protected phenomena
such as those originating from triangle anomaly. The presentation is oriented
to non-experts on these fields, and hence relies on intuitive pictures of the
methods and the results, without going into specific details.Comment: 8 pages, Prepared for the proceeding of the conference "Quark Matter
2012", Washington DC, August 13-18, 201
Chiral Magnetic Effect at Weak Coupling with Relaxation Dynamics
We provide a resolution of an old issue in weak coupling computation of the
Chiral Magnetic Effect (CME) current, where a free chiral fermion theory gives
two different results depending on the order of the two limits,
(frequency) and (spatial momentum). We
first argue based on hydrodynamics that in any reasonable interacting theory of
chiral fermions the non-commutativity between the two limits should be absent,
and we demonstrate this at weak coupling regime in two different frameworks:
kinetic theory in the relaxation time approximation, and diagrammatic
computation with resummation of damping rate. In the latter computation, we
also show that the "pinch" singularity, which would make the summation of
ladder diagrams necessary as in the P-even correlation function, is absent in
the relevant P-odd correlation function. The correct value of CME current is
reproduced even in the presence of relaxation dynamics in both computations.Comment: 26 pages, 3 figure
Out-of-Equilibrium Chiral Magnetic Effect at Strong Coupling
We study the charge transports originating from triangle anomaly in
out-of-equilibrium conditions in the framework of AdS/CFT correspondence at
strong coupling, to gain useful insights on possible charge separation effects
that may happen in the very early stages of heavy-ion collisions. We first
construct a gravity background of a homogeneous mass shell with a finite
(axial) charge density gravitationally collapsing to a charged blackhole, which
serves as a dual model for out-of-equilibrium charged plasma undergoing
thermalization. We find that a finite charge density in the plasma slows down
the thermalization. We then study the out-of-equilibrium properties of Chiral
Magnetic Effect and Chiral Magnetic Wave in this background. As the medium
thermalizes, the magnitude of chiral magnetic conductivity and the response
time delay grow. We find a dynamical peak in the spectral function of retarded
current correlator, which we identify as an out-of-equilibrium chiral magnetic
wave. The group velocity of the out-of-equilibrium chiral magnetic wave is
shown to receive a dominant contribution from a non-equilibrium effect, making
the wave moving much faster than in the equilibrium, which may enhance the
charge transports via triangle anomaly in the early stage of heavy-ion
collisions.Comment: 1+35 pages, 8 figures. References added. Published versio
Second Order Transport Coefficient from Chiral Anomaly at Weak Coupling: Diagrammatic Resummation
We compute one of the second order transport coefficients arising from the
chiral anomaly in a high temperature weakly coupled regime of quark-gluon
plasma. This transport coefficient is responsible for the CP-odd current that
is proportional to the time derivative of the magnetic field, and can be
considered as a first correction to the chiral magnetic conductivity at finite,
small frequency. We observe that this transport coefficient has a non-analytic
dependence on the coupling as at weak coupling regime,
which necessitates a re-summation of infinite ladder diagrams with leading
pinch singularities to get a correct leading log result: a feature quite
similar to that one finds in the computation of electric conductivity. We
formulate and solve the relevant CP-odd Schwinger-Dyson equation in real-time
perturbation theory that reduces to a coupled set of second order differential
equations at leading log order. Our result for this second order transport
coefficient indicates that chiral magnetic current has some resistance to the
time change of magnetic field, which may be called "chiral induction effect".
We also discuss the case of color current induced by color magnetic field.Comment: 54 pages, 8 figure
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