1. A charged massless quark in a magnetic field
Transcript of 1. A charged massless quark in a magnetic field
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1
Defu Hou
Central China Normal University, Wuhan
phases of QCD &BES @ Fudan Uni. Aug15-18 , 2017
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Outline
I. Introduction to anomalous transport
II. CME with non-constant Axial & B
III. Subtlety of the Wigner function used for CME
IV CME on lattice and Higher order correction
V. Conclusion and outlook
5
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I. Introduction : Anomalous Transports
Micro-quantum anomaly + B/ Ω macro-transport (CME/CVE)
Micro
Macro
Search in HIC
Astrophysics, cosmology
Nature Phys.12(2016)
Phys. Rev. X.5(2015)
Science350(2015)413
B Ω
(Fukushima-Kharzeev-Warringa, Son-Zhitnitsky, Vilenkin
X.Huang , Rep.prog. Phys. (2016)
Kharzeev,Liao,Voloshin,Wang: Prog.Part.Nucl.Phys.2016
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Strong EM Field/Rotation/polarization produced in HIC
Deng, Huang, 2015
Jiang,Lin,Liao, 2016
Li, Sheng, Wang 2016
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Net axial charge generated
𝜕𝜇𝑗5𝜇= −
𝑞2𝑁𝑐16𝜋2
𝐹 ෨𝐹 −𝑔2𝑁𝑓
8𝜋2𝑡𝑟𝐺 ෨𝐺 + 2𝑖𝑚 ത𝜓𝛾5𝜓
𝐹 ෨𝐹
𝑡𝑟𝐺 ෨𝐺
Parallel electric and magnetic
fields
Topological field configurations(instanton, sphaleron)
Parallel chromo electric and magnetic fields
2𝑖𝑚 ത𝜓𝛾5𝜓 Explicit breaking by quark
mass
All three can lead to net axial charge 𝑁5 = 𝑑3𝑥 𝑗50
HIC
HIC
condensed matter
(See S. Lin’s talk on Friday)
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• Theoretical investigations:
Field theory
Holography
Hydrodynamics & Kinetic theory
• Experimental situation in HIC (See H.Z.Huang’s talk)
Off central collisions generate inhomogeneous & transient
axial charge produced via topological fluct. plus mass effect(See S. Lin’s talk on Friday)
Beyond thermal equilibrium
B
D. T. Son et. al., PRL103, 2009, PRL106, 2011; Stephanov, Yin, PRL (2012)
Gao, Liang, Pu, Q Wang, XN Wang PRL109 2012,
Anomalous Viscous Fluid Dynamics (AVFD): Jiang, Shi, Yin, JL, PLB (2015);
arXiv:1611.04586.
K. Fukushima et. al., Phy. Rev. D. 78, 074033, 2008Hou , Liu , Ren , JHEP 1105: 046, 2011
D. Kharzeev et. al., arXiv: 1312.3348
Yee. Rebhan et. al., JHEP 0911: 085, 2009
Shu Lin et. al., PRL114, 2015; PRD88. 2013
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General properties and Subtleties
1 2( , )Q Q
Axial anomaly:
Vector Ward identity:
Naive Axial Vector Ward identity
UV diverge→ impossible to maintain(1)&(2)Gauge invariance→ vector Ward identity
Anomaly,
Universal to all orders of coupling,all temperature &
chemical potential .Necessary to explain
5J J J
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Anomalous, Ward identity in an electromagnetic field 2
5 22
l leJ i F F
x x
2
24
AeChern Simons i A
x
Naïve axial charge Q_5 is not conserved
Conversed axial charge
3
5 5 4
5 0
Q Q i d r
dQ
dt
Should be used in the equilibrium thermodynamics
(Rubakov)
Q
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9
0
2
1
2
1k,kqJ
2,
2
1 0kkqB
, 05 kk
II. Non-constant & B / Subtlety of Constant Limits
0),( and 0),( 0 qk k
CME in general
Constant limit:
2
522
e
J BAlways gives ?
Hou, Ren, Liu JHEP 05(2011)046
2
C f
f
N q Color-flavor factor
5
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10
0
2
1
2
1k,kqJ
2,
2
1 0kkqB
, 05 kk
0 0limit limit q
Constant , non-constant B:2
522
e
J B
5
0 0limit limitq
2
52
1
3 2
e
J B
Artifact of one-loop approximation. The ambiguity disappears
with higher order corrections. (Satow & Yee)
00k k
Kharzeev
& Warringar
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, 05 kk
00 0limit limitk k
Constant B, non-constant
0J
0 0 0limit limitk k
2
522
e
J B
Follows from the EM gauge invariance and the non-
renormalization of the axial anomaly. Valid to all orders!
with T=0 and : relativistic invariance requires
the two limit orders are equivalent:
0
0J
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IR limit Higher order
0 none
none if IR safe
yes
0 none
00limlimq
0 0limlimq
0 00lim lim
kk
0 0 0lim limk k
2
522
e B 2
521
3 2
e B
0 00lim limkk
0 0 0lim limk k 0
0
T
0
/
0
T
and or
CMEJ
0
0
T
0 00lim lim
kk
0 0 0lim limk k
0 00lim lim
kk
0 0 0lim limk k
00limlimq
0 0limlim
q
0050
2
1,
2
1 & , vs.
2
1,
2
1kkkCME kqBkkqJ
0
and/or
0
T
CMEJ
B52
2
2
e
B52
2
23
1
e
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• Wigner function formulation
The Wigner function that links various hydrodynamic quantities of the
system to the Green's function
Gao et al obtain CME& CVE and axial anomalies with a constant
(see S. Pu’s talk )
5
III. Subtlety of the Wigner function used for CME
inhomogeneous and transient ? 5
Gao, Liang, Pu, qWang, xnWang (2012)
,
Vasak, Gyulassy , Elze (1987), Heinz et al ( non-abelian plasma) (96)
Wu,Hou, Ren, 2016
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• The electric current extracted from the wigner function
),(tr2
)(4
4
pxWpd
iexJ
)()(),()(44 xxxxUyydie
),(lim0
yxJy
)()(),(),( xxxxieUyxJ
For a constant 52
52
1 with
2 2
fluid velocity
eJ B B u F
u
For a non-constant , it is problematic because of UV
divergence with the limit 5
0y
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Considering a massless Dirac field in an external and A 5A
*The Lagrangian density:
)( 55AiieAL
with ),( 555 iAA
*The action:
xLddtS 3
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* The electric current
0),(),(tr
0),(),(tr),(
0
2
22
0
1
11
yyxJxxSie
yyxJxxSieyxJ
• Closed time path Green function formation
),(),(
),(),(),(
2221
1211
yxSyxS
yxSyxSyxSCTP
)]()([~
),()()(),(
)()(-),()]()([),(
2221
1211
yxTyxSyxyxS
xyyxSyxTyxS
:T :T~
time ordering anti-time ordering
* A fermion propagator
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5
2
55
1
5
21 ,,, with
gauge link:
)()(1),( 2AOAdiexxUx
x
* Expansion to the linear order in and A 5A
)()()()()(
)()()()()(
)()()(
)()()(),(
),(
152151222
4
1
4
251112522
4
1
4
4
55
4
zAzAxzSzzSzxSzdzde
zAzAxzSzzSzxSzdzde
zAxzSzxzSde
zAxzSzxzSdxxS
xxS
da
d
cd
c
ac
cd
ca
c
dc
d
ad
cd
cb
c
ac
c
cb
c
ac
c
ab
ab
full propagator:
free propagator
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Problems of the Wigner function formalism
* The nonconserversion of the electric current
)()(2)()(
8),( 5252
xAx
xFy
yyxFxF
iyxJ
x
x
A
x
AxF
x
A
x
AxF
555 )(
,)(with
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** by averaging the direction of y
)()(32
3)0,()( 52
xFxFi
xJx
xJx
unless the axial potential is a pure gradient
0 J
The electric current is not conserved!
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* An incosistency
In principle, the electric current should satisfy the consistency
)(
)'(
)'(
)(
xA
xJ
xA
xJ
However, the electric current from Wigner function:
)'()(
2)(
)','(
)'(
),(45
22xx
x
xA
y
yyi
xA
yxJ
xA
yxJ
Averaging the direction of y
)'(16
3
)(
)','(
)'(
),(4
52xxF
i
xA
yxJ
xA
yxJ
The consistency condition broken!
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Applying to a general chiral case, the present
form of the Wigner function formulation
needs to be revised!
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correction : the regulated Wigner function
)( 55AiieAL
)()(),(lim
),(tr2
)(
0
4
4
xxxxUi
pxWpd
ixJ
y
a robust regularization scheme has to be introduced to the
underlying field theory before defining the wigner function.
PV regulator
should be
included in it
e.g. If the underlying field theory is regularized by PV scheme
)(
)'(
)'(
)(
xA
xJ
xA
xJ
0 J
But the CME current would also be cancelled.
The Bardeen like term should be added in.
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CME current canceled at thermal equilibrium.
gives CME current :
Wu,Hou, Ren, 2016
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Phenomenological implications of the
subtleties regarding the order of limits
Axial charge generated via toplogical fluctuations dictated
by the stochastic Eq with a white noise
In Momentum sapce
Corresponding an axial potential
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Average current vanishes, the correlation funct.
is dominated by diffusion pole
If the homog. \mu_5 is a good approximation and
classic form of CME current emerges ---Noneq. Phenom.
Towards equilibrium,
Inverse limit-order prevails, and CME current disappears,
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CME on Lattice
using lattice QCD with Wilson term
Karsten and Smit (1981)
Yamamoto,PRL(2011)
See Bo Feng”s talk
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One-loop self-energy on lattice of size
CME vanishes at continu. limit .
At zero temperature
Feng,Hou, Liu, Ren, Wu, PRD95,(2017)
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Kubo formula:
→q q→0
Son & Surowka
Under B & vorticity
Higher order correction to CVE
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Triangle anomaly & hydrodynamics & thermodynamics
• Possible relation with the gravity anomaly→ No ( Landsteiner et.al)
• Coleman-Hill theorem for a field theory without gauge degrees of
freedom at all→(Golkan & Son)
• A field theory with gauge degrees of freedom?
D. T. Son & P. Surowka
Y. Neiman & Y. Oz
One-loop calculation Landsteiner et. al. C=1/12
Any higher order connection to c ?
Kinetic theory , Stephenov, Gao et.al.
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Higher order correction to CVE
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Are there any corrections from higher orders ?
S. Golkar and D. T. Son, arXiv:1207.5806 : No (Yes)
Hou,Liu,Ren, PRD86 (2012) 121703®
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• The zero P & zero E limits of do not commute and the
difference is robust against Higer Order correction
• While the CSE is expected in RHIC, its magnitude may not
reach the ideal value because of inhomogeneity
• Nonrenormalization is true for most but not for all anomal.
transp. coefs . We obtained 2-loop correction to CVE coef.
• Naive Wigner function can not be applicable to the case with
non-constant . The problem stems from axial anomaly .
The PV regulated WF leads consistent results
. We examine the issues raised here with lattice formulation
we obtained the same results as that in continuous case
with QFT and Wigner function method .
2
522
e
J B
V. Concluding Remarks
5
5
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B.Feng, H. Liu, H-c, Ren, Y. Wu
Thank you very much for your
attention!
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