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Masayasu Harada (Nagoya Univ.)

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Dilepton Production from Dropping Rho

in the Vector Manifestation

Masayasu Harada(Nagoya Univ.)

at Chiral 07 (Osaka, November 14, 2007)

based on

M.H. and C.Sasaki, Phys.Rev.D74:114006,2006

see also

M.H. and K.Yamawaki, Phys. Rept. 381, 1 (2003)

M.H. and C.Sasaki, Phys. Lett. B 537, 280 (2002)

M.H., Y. Kim and M. Rho, Phys. Rev. D 66, 016003 (2002).

M.H. and C.Sasaki, Nucl. Phys. A 736, 300 (2004)

1. Introduction

☆ ＱＣＤ in hot and dense matter

T

Quark-Gluon-Plasma phase

Color-Superconducting

phase

Hadron phase

μB

☆ Melting of quark – anti-quark condensate

〈 q q 〉

Is there a signal ?

☆ Brown-Rho scaling

G.E.Brown and M.Rho, Phys. Rev. Lett. 66 2720 (1991)

dropping r mass ⇔ chiral symmetry restoration

Theoretical description of dropping r mass.

☆ Vector Manifestation

M.H. and K.Yamawaki, Phys. Rev. Lett. 86, 757 (2001)

M.H. and C.Sasaki, Phys. Lett. B 537, 280 (2002)

M.H., Y. Kim and M. Rho, Phys. Rev. D 66, 016003 (2002).

near chiral restoration point

longitudinal r= Chiral partner of p

Dropping r mass

・・・ signal of the chiral restoration based on the VM.

R.Rapp-J.Wambach, ANP 25,1 (2000)

dropping r mass

based on Brown-Rho scaling

☆ Dropping r/w mass (Brown-Rho scaling) can explain

KEK-PS E325

CB/TAPS@ELSA

☆ Strong violation of the VD・・・ Prediction of the VM

gives a substancial suppression !

G. E. Brown and M. Rho, arXiv:nucl-th/0509001; arXiv:nucl-th/0509002.

☆ Recent experiments exclude dropping ρ ?

CERES : Talk given by P. Braun-Munzinger at KIAS-APCTP Workshop

"Relativistic Heavy-Ion Collison : Present and Future" 2006-09 Heavy Ion Meeting (HIM 2006-09).

NA60 Nucl.Phys.A774:715-718,2006.

dropping ρ??

☆ These analyses seem to assume the vector dominance (VD).

Effect from the violation of the VD to the rate ?

Outline

1. Introduction

2. Hidden Local Symmetry

and the Vector Dominance

3. Thermal Dilepton Spectra

in the Vector Manifestation

4. Summary

2. Hidden Local Symmetry and the Vector Dominance

◎ Hidden Local Symmetry

・・・ EFT for r and pbased on chiral symmetry of QCD

M. Bando, T. Kugo, S. Uehara, K. Yamawaki and T. Yanagida, PRL 54 1215 (1985)

M. Bando, T. Kugo and K. Yamawaki, Phys. Rept. 164, 217 (1988)

r = gauge boson of the HLS

massive through the Higgs mechanism

◎ Systematic low-energy expansion including dynamical r

H.Georgi, PRL 63, 1917 (1989); NPB 331, 311 (1990):

M.H. and K.Yamawaki, PLB297, 151 (1992); M.Tanabashi, PLB 316, 534 (1993):

M.H. and K.Yamawaki, Physics Reports 381, 1 (2003)

loop expansion ⇔ derivative expansion

†

U=e= ξ ξ

L

R

2iπ/ F

π

F , F・・・ Decay constants of π and σ

π

σ

2

m = ag F

2

2

π

ρ

h ∈ ［SU(N ) ］

f

V

local

◎ 3 parameters at the leading order

g ∈ ［SU(N ) ］

Fp・・・ pion decay constant

g・・・ gauge coupling of the HLS

a = (Fs/Fp)2 ⇔ validity of the vector dominance

f

L,R

global

L,R

☆ Hidden Local Symmetry

・ Particles

ρμ = ρμaTa・・・ HLS gauge boson

π=πaTa・・・ NG boson of ［SU(Nf)L×SU(Nf)R］global symmetry breaking

σ=σaTa・・・ NG boson of ［SU(Nf)V］local symmetry breaking

◎ HLS analysis[M.H. and K.Yamawaki, Phys. Rept. 381, 1 (2003)]

・ a = 4/3 in the large Nc limit

・ a = 2 including 1/Nc corrections

cf: AdS/QCD anlysis by Sakai-Sugimoto, PTP143,843 (2005)

see also AdS/QCD analysis by

M.H., M.Matsuzaki and K.Yamawaki, PRD74, 076004 (2006).

r dominance is accidental only for Nc = 3 (and T = 0)

☆ Vector dominance (r dominance) at T = 0

e+

e-

a/2

1 – a/2

a = 2 ⇒ vector dominance

long standing problem not clearly explained in QCD !

e+

e-

☆ r dominance at T > 0 ?

a/2

1 – a/2

0 → 1

1 → 1/2

◎ a = 2 kept fixed in several analyses (No T-dependence on a)

◎ Parameters of hadronic Lagrangians depend on T.

・・・Intrinsic temperature dependence

signature of internal structure of hadrons

(Hadrons are constructed from quarks and gluons.)

・ VM predicts a(T) → 1whenmr(T) → 0forT → Tc

Strong violation of r dominance in the VM

Strong suppression of r contribution to the dilepton spectrum

☆ Intrinsic temperature dependence of parameters

・・・ obtained by integrating out heavier hadrons

・ Effects of heavy hadrons are negligible ?

・・・ Not True near the critical temperature

e.g., Hagedon temperature based on string model

large Nc QCD

each contribution from hadrons is suppressed by 1/Nc

phase transition is driven by infinite number of hadrons

・ Infinite number of hadrons contribute near Tc

in real-life QCD

Integrating out infinite number of hadrons near Tc

→ a large T dependence of the parameters

for effective models for light hadrons

(e.g., π and ρ in the HLS)

☆ Vector Manifestation

M.H. and K.Yamawaki, Phys. Rev. Lett. 86, 757 (2001)

・・・ Wigner realization of chiral symmetry

longitudinalρ ＝ chiral partner of π

c.f. conventional linear-sigma model manifestation

scalar meson = chiral partner of π

Quark Structure and Chiral representation

(S. Weinberg, 69’)

coupling to currents and densities

longitudinal components

Chiral Restoration

vector manifestation

linear sigma model

mρ → 0 is necessary

・・・ support BR scaling

☆ T-dependences of physical parameters

・・・ intrinsic T dependence

+ hadronic temperature effects from thermal π and ρ

intrinsic T dependence for T > Tf = 0.7 Tc

ρ mass

mρ → 0

ρ width

Γρ → 0

a

Tf/Tc

Tf/Tc

◎ Intrinsic T dependence

・・・ basic ingredient for the Vector Manifestation (VM)

◎ VM predicts

; dropping r

; strong violation of the vector dominance

◎ Vector dominance ?

direct γππ coupling ： 1 – a/2

Tf/Tc

strong violation

of the VD

VD is good

・ Strong violation of the VD occurs near Tc

due to the intrinsic effect.

3. Thermal Dilepton Spectra in the VM

M.H. and C.Sasaki, Phys.Rev.D74:114006,2006

T = 0.4 Tc

No much difference !

☆ Effect of violation of the vector dominance

VM (forT → Tc)

a(T) → 1

whenmr(T) → 0

VM with VD

a(T) = 2 kept fixed

whenmr(T) → 0

v.s.

T = 0.8 Tc

vacuum ρ< VM < VM with VD

T = 0.85 Tc

vacuum ρ≪ VM ≪ VM with VD!!

Signal of the VM

Violation of VD is very important

◎ Near Tc

T = 0.75 Tc

VM with VD

vacuum ρ

VM < vacuum ρ< VM with VD!!

VM

◎ Hidden Local Symmetry Theory・・・ EFT for r and p

Systematic chiral perturbation including dynamical r

◎ Vector dominance in the HLS

・ a = 4/3 in the large Nc limit

・ a = 2 including 1/Nc corrections

◎ Vector Manifestationin hot matter ・・・ mρ → 0 for T → Tc

⇒ mρ→ 0・・・ signal of the chiral symmetry restoration !

4. Summary

・ strong violation of the VD

・・・ important for the dilepton rate

◎ future direction

・ Effects of collisional broadening including A1, …

・・・ work in progress (M.H., C.Sasaki and W.Weise)

The End