Holographic model of the thermal phases of QCD

Tel Aviv University

Fri, Feb. 16th 2007, 11:00

Salle Claude Itzykson, Bât. 774, Orme des Merisiers

We construct and analyze a holographic model of the thermal phases of
QCD.
It is based on Sakai-Sugimoto model,
which is a holographic dual of a theory which spontaneously breaks a
$U(N_f)_L\times U(N_f)_R$ chiral flavor symmetry at zero
temperature. The theory involved is a $4+1$ dimensional supersymmetric
$SU(N_c)$ gauge theory compactified on a circle of radius $R$ with
anti-periodic boundary conditions for fermions, coupled to $N_f$
left-handed
quarks and $N_f$ right-handed quarks which are localized at different
points on the
compact circle (separated by a distance $L$). In the supergravity
limit which we analyze, the theory undergoes a deconfinement phase
transition at a temperature $T_d = 1 / 2\pi R$. For quark separations
obeying
$L > L_c \simeq 0.97*R$
the chiral symmetry is restored at this temperature, but for
$L < L_c \simeq 0.97*R$ there is an intermediate phase which is
deconfined
with broken chiral symmetry, and the chiral symmetry is restored at
$T_{\chi SB} \simeq 0.154 / L$.
All of these phase transitions are of first order.
We further analyse the mesonic spectra at finite temperature.
The temperature dependence of low-spin as
well as high-spin meson masses is shown to exhibit a pattern
familiar from the lattice. Furthermore, we find the dissociation
temperature of mesons as a function of their spin, showing that
at a fixed quark mass, mesons with larger spins dissociate at lower
temperatures. The Goldstone bosons associated with chiral symmetry
breaking are shown to disappear above the chiral symmetry
restoration temperature. Finally, we show that holographic
consideration imply that large-spin mesons do not experience drag
effects when moving through the quark gluon plasma.