the chiral magnetic effect: from quark-gluon plasma to dirac semimetals
Post on 16-Jan-2016
58 Views
Preview:
DESCRIPTION
TRANSCRIPT
1
The chiral magnetic effect:from quark-gluon plasma to Dirac semimetals
D. Kharzeev
High Energy Physics in the LHC Era, Valparaiso, Chile, 2012 “Quarks – 2014”, Suzdal, Russia, 2-8 June,
2014
What is Chiral Magnetic Effect?
2
Chirality imbalance + Magnetic field =Electric current
Talks at “Quarks 2014”:V. Braguta, T. Kalaydzhyan, A. Kotov
Quantum anomalies
3
Anomalies: The classical symmetry of the Lagrangian is broken by quantum effects - examples: chiral symmetry - axial anomaly scale symmetry - scale anomaly
Anomalies imply correlations between currents:
e.g.
decay
A
V V
if A, V are background fields,V is not conserved!
Quantum anomalies
4
A
In classical background fields (E and B), chiralanomaly induces a collective motionin the Dirac sea
Chiral Magnetic Effectin a chirally imbalanced
plasmaFukushima, DK, Warringa, PRD‘08
In the presence of the chiral chemical potential and in magnetic field, the vector e.m. current is not conserved:
Compute the current through
The result:
Coefficient is fixed by the axial anomaly, no corrections5
Some of the earlier work on
P-odd currents
6
Vilenkin ’78Eliashberg ’83Rubakov, Tavkhelidze, ‘85Levitov, Nazarov, Eliashberg ’85Wilczek ‘87Alekseev, Cheianov, Frohlich ‘98Joyce, Shaposhnikov ‘97…Review: DK, Prog. Part. Nucl. Phys. 2014
Chiral magnetic conductivity:
discrete symmetries
7
P-evenT-odd
P-odd
P-odd
P-oddT-odd
P-odd effect!
T-evenNon-dissipative
current!(quantum computing etc)
cf Ohmicconductivity:
P-even, T-odd,dissipative
Systematics of anomalous conductivities
8
Vectorcurrent
Axialcurrent
Magnetic field
Vorticity
46
Heavy ion collisions as a source of the strongest magnetic fields available in
the Laboratory
DK, McLerran, Warringa, Nucl Phys A803(2008)227
47
Heavy ion collisions: the strongest magnetic field ever achieved in the laboratory
46
Magnetic fields in heavy ion collisionsIn a conductingplasma, Faradayinduction can makethe field long-livedK.Tuchin, arXiv:1006.3051, 1305.5806
U.Gursoy, DK, K. Rajagopal, arXiv:1401.3805
L.McLerran,V.Skokov arXiv:1305.0774
46
Magnetic fields in heavy ion collisionsU.Gursoy, DK, K. Rajagopal, arXiv:1401.3805
Observable effects on directed flow of charged hadrons:
Faraday
Faraday + Hall
“Numerical evidence for chiral magnetic effect in lattice gauge theory”,P. Buividovich, M. Chernodub, E. Luschevskaya, M. Polikarpov, ArXiv 0907.0494; PRD
SU(2) quenched, Q = 3; Electric charge density (H) - Electric charge density (H=0)
Red - positive chargeBlue - negative charge
“Chiral magnetic effect in 2+1 flavor QCD+QED”,M. Abramczyk, T. Blum, G. Petropoulos, R. Zhou, ArXiv 0911.1348;
2+1 flavor Domain Wall Fermions, fixed topological sectors, 16^3 x 8 lattice
Red - positive chargeBlue - negative charge
Electric dipole moment of QCD instanton in an external magnetic field
15
G. Basar, G. Dunne, DK, arXiv:1112.0532 [hep-th]
Topological charge density
Quark zero mode density
Asymmetry between leftand right modes induces the e.d.m. in an external B
B=0B>0
16
Arxiv:1401.4141
17
No sign problem for the chiral chemical potential - direct lattice studies are possible
Fukushima, DK, Warringa, PRD‘08
18
arXiv:1105.0385, PRL + Talks by V. Braguta and A. Kotov
The Chern-Simons diffusion rate in an external magnetic
field
19
G. Basar, DK, Phys Rev D, arXiv:1202.2161
strongly coupled N=4 SYM plasma in an external U(1)R
magnetic field through holography
weak field:
strong field increases the rate:
dimensional reduction
Holographic chiral magnetic effect:the strong coupling regime (AdS/CFT)
H.-U. Yee, arXiv:0908.4189,JHEP 0911:085, 2009;V. Rubakov, arXiv:1005.1888, ...
A. Rebhan, A.Schmitt, S.Stricker JHEP 0905, 084 (2009), G.Lifshytz, M.Lippert, arXiv:0904.4772;.A. Gorsky, P. Kopnin, A. Zayakin, arXiv:1003.2293, T. Kalaydzhyan, I. Kirsch ‘11,..
CME persists at strong coupling - hydrodynamical formulation?
D.K., H. Warringa Phys Rev D80 (2009) 034028
Strong coupling
Weak coupling
Hydrodynamics and anomalies
• Hydrodynamics: an effective low-energy TOE. States that the response of the fluid to slowly varying perturbations is completely determined by conservation laws (energy, momentum, charge, ...)
• Conservation laws are a consequence of symmetries of the underlying theory
• What happens to hydrodynamics when these symmetries are broken by quantum effects (anomalies of QCD and QED)?
21
Chiral MagnetoHydroDynamics (CMHD) -
relativistic hydrodynamics with triangle anomalies and external
electromagnetic fields
22
First order (in the derivative expansion) formulation:D. Son and P. Surowka, arXiv:0906.5044
Constraining the new anomalous transport coefficients:positivity of the entropy production rate,
CME(for chirallyimbalancedmatter)
Chiral MagnetoHydroDynamics (CMHD) -
relativistic hydrodynamics with triangle anomalies and external
electromagnetic fields
23
First order hydrodynamics has problems with causality and is numerically unstable, so second order formulation is necessary;
Complete second order formulation of CMHD with anomaly:DK and H.-U. Yee, 1105.6360; Phys Rev D
Many new transport coefficients - use conformal/Weyl invariance;still 18 independent transport coefficients related to the anomaly. 15 that are specific to 2nd order:
new
Many new anomaly-induced phenomena!
Chiral MagnetoHydroDynamics (CMHD) -
relativistic hydrodynamics with triangle anomalies and external
electromagnetic fields
24
DK and H.-U. Yee, 1105.6360Positivity of entropy
production - still too many unconstrained transport coefficients...
Is there another guiding principle?
No entropy production from
T-even anomalous terms
25
P-evenT-odd
P-odd
P-odd
P-oddT-odd
P-odd effect!
T-even Non-dissipative current!
(time-reversible - no arrow of time, no entropy production)
cf Ohmicconductivity:
T-odd,dissipative
DK and H.-U. Yee, 1105.6360
No entropy production from
P-odd anomalous terms
26
DK and H.-U. Yee, 1105.6360
Mirror reflection:entropy decreases ?
Decrease is ruled out by 2nd law of thermodynamics
Entropy grows
No entropy production from
T-even anomalous terms
27
1st order hydro: Son-Surowka results are reproduced
2nd order hydro: 13 out of 18 transport coefficients are computed; but is the “guiding principle” correct?
Can we check the resulting relations between the transportcoefficients? e.g.
DK and H.-U. Yee, 1105.6360
The fluid/gravity correspondence
28DK and H.-U. Yee, 1105.6360
Long history: Hawking, Bekenstein, Unruh; Damour ’78; Thorne, Price, MacDonald ’86 (membrane paradigm) Recent developments motivated by AdS/CFT: Policastro, Kovtun, Son, Starinets ’01 (quantum bound) Bhattacharya, Hubeny, Minwalla, Rangamani ’08 (fluid/gravity correspondence)
Some of the transport coefficients of 2nd order hydro computed; enough to check some of our relations, e.g.
J. Erdmenger et al, 0809.2488;N. Banerjee et al, 0809.2596 It
works
Other holographicchecks work as well:
The chiral magnetic current is non-dissipative:
protected from (local) scattering and dissipation by (global)
topology
Somewhat similar to superconductivity, but can exist
at high temperature!
Anomalous transport coefficients in hydrodynamics describe dissipation-free processes (unlike e.g. shear viscosity)
29
DK, H.-U. Yee, arXiv:1012.6026 [hep-th];PRD
The CME in relativistic hydrodynamics: The Chiral
Magnetic Wave
30
Propagating chiral wave: (if chiral symmetry is restored)
Gapless collective mode is the carrier of CME current in MHD:
CME Chiral separation
Electric
Chiral
The Chiral Magnetic Wave
31
DK, H.-U. Yee, arXiv:1012.6026 [hep-th], PRD
The velocity of CMWcomputed in Sakai-Sugimotomodel (holographic QCD)
In strong magnetic field, CMW propagates with the speed of light!
Chiral
Electric
32
Testing the Chiral Magnetic Wave
Y.Burnier, DK, J.Liao, H.Yee,PRL 2011
Finite baryon density + CMW = electric quadrupole moment of QGP.
Signature - difference of elliptic flows of positive and negative pions determined by total charge asymmetry of the event A: at A>0, v2(-) > v2(+); at A<0, v2(+) > v2(-)
33
G. Wang et al [STAR Coll],arxiv:1210.5498 [nucl-ex]
Testing the CMW at RHIC
34
CME @ Quark Matter 2014:
ALICE Coll, Talk by R.Belmont
ALICE Coll. at the LHC
35
CME @ Quark Matter 2014:
STAR Coll, Talk by Q-Y Shou
ALICE Coll, Talk by R.Belmont
36
Exciting the CMW by electromagnetic fieldsM.Stephanov, H.-U.Yee,arxiv:1304.6410
The first numerical simulationof CMHD!M.Hongo, Y.Hirono, T.Hirano,arxiv: 1309.2823
Dirac and Weyl semimetals
The discovery of Dirac semimetals – 3D chiral materials
Z.K.Liu et al., Science 343 p.864 (Feb 21, 2014)
The discovery of Dirac semimetals – 3D chiral materials
Z.K.Liu et al., Science 343 p.864 (Feb 21, 2014)
Ongoing experimental studies of the Chiral Magnetic Effect
Chiral electronics
40
quantum amplifier -sensor of ultra-weakmagnetic fieldDK, H.-U.Yee,Phys.Rev.B 88(2013) 115119
Dirac semimetal The Kirchhoff’s law
for this circuit possessesan instability
SummaryInterplay of topology, anomalies and
magnetic field leads to the Chiral Magnetic Effect;
confirmed by lattice QCD x QED, evidence from RHIC and LHC
CME and related anomaly-induced phenomena
are an integral part of relativistic hydrodynamics
(Chiral MagnetoHydroDynamics)
Ongoing experimental studies of CME in Dirac semimetals; potential applications
The Chern-Simons diffusion rate in an external magnetic field
42
G. Basar, DK, arXiv:1202.2161 (PRD’12)
strongly coupled N=4 SYM plasma in an external U(1)R
magnetic field through holography
Dual geometry:
Constant magnetic flux in x3 direction:start with a general 5D metric and
look for asymptotically AdS5 solutions of Einstein-Maxwell equations with a horizonsolutions interpolate between BTZ black hole x T2 (small r) and AdS5 (large r) RG flow from D=3+1 CFT at short distances, and D=1+1 CFT at large distances
E.D’Hoker, P.Krauss, arXiv:0908.3875
top related