FIAS Scientific Report 2011 - Frankfurt Institute for Advanced Studies ...

Trace anomaly and the vector coupling in dense matter
Collaborators: C. Sasaki 1 , H.K. Lee 2 , W.-G. Paeng 2 , M. Rho 2,3
1 Frankfurt Institute for Advanced Studies, 2 Department of Physics, Hanyang University, Seoul, Korea 3 Institut de
Physique Théorique, CEA Saclay, Gif-sur-Yvette cédex, France
In nuclear physics, a scalar meson plays an essential role as known from Walecka model that works fairly well
for phenomena near nuclear matter density. On the other hand, at high density, the relevant Lagrangian that has
correct symmetry is the linear sigma model, and the scalar needed there is the fourth component of the chiral
four-vector (�π,σ). Thus in order to probe highly hot/dense matter, we have to figure out how the chiral scalar
at low temperature/density transmutes to the fourth component of the four-vector.
In this work we have presented how an effective theory near chiral symmetry restoration emerges from the
dilaton-implemented HLS Lagrangian as illustrated in Fig. 1, and discussed its phenomenological implications
at high baryon density. The soft dilaton is responsible for the spontaneous breaking of the scale symmetry and
its condensate vanishes when the chiral symmetry is restored. In fact, topological stability of the half-skyrmion
phase has been observed. This is a strong indication that the configuration is robust and it could be associated
with the scale symmetry restoration at high density in continuum theories.
Our main observation on the suppressed repulsive interaction is a common feature in the two different assignments,
“naive” and mirror, of chirality. The nucleon mass near chiral symmetry restoration exhibits a striking
difference in the two scenarios. How the suppression of the repulsion at the dilaton limit – which seems to be
universal independent of the assignments but may manifest itself differently in the two cases – will affect the
EoS for compact stars is an interesting question to investigate.
π
1
σ
π
P
2
Q
π
3
dilaton limit chiral restoration
T or
NLSM
ms >> mpi
LSM
ms > mpi ms = mpi
Figure 1: (Left) A chiral sphere in (�π,σ) space. P on the sphere is mapped to another point Q via chiral transformations.
(Right) Expected changeover of effective theories near chiral symmetry restoration.
Related publications in 2011:
1) C. Sasaki, H. K. Lee, W. -G. Paeng and M. Rho, Conformal anomaly and the vector coupling in dense
matter, Phys. Rev. D84, 034011 (2011), arXiv:1103.0184 [hep-ph].
2) W. -G. Paeng, H. K. Lee, M. Rho and C. Sasaki, Dilaton-limit fixed point in hidden local symmetric parity
doublet model, arXiv:1109.5431 [hep-ph], submitted to Physical Review D.
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