13-19 May 2018
Venice, Italy
Europe/Zurich timezone
The organisers warmly thank all participants for such a lively QM2018! See you in China in 2019!

Tachyonic instability of the scalar mode prior to the QCD critical point based on the functional renormalization-group method in the two-flavor case

15 May 2018, 17:00
2h 40m
First floor and third floor (Palazzo del Casinò)

First floor and third floor

Palazzo del Casinò

Poster Phase diagram and search for the critical point Poster Session


Takeru Yokota (Kyoto University, Japan)


We investigate spectral properties of the collective excitations around the QCD critical point (CP) by applying the functional renormalization-group (FRG) method to the two-flavor quark-meson model with current quark mass $m_q$ being varied. The nature of the CP such as the soft modes is known to be affected by the value of $m_q$: We first determine the whole phase structure in the three-dimensional space $(T, μ, m_q)$ consisting of temperature $T$, quark chemical potential $\mu$ and $m_q$, with the tricritical point, $\mathrm{O}(4)$ and $\mathrm{Z}_2$ critical lines being located; they altogether make a winglike shape quite reminiscent of those known in the condensed matters with a tricritical point. We then calculate the spectral functions in the scalar and pseudoscalar channel around the critical points. We find that the sigma mesonic mode becomes tachyonic with a superluminal velocity at finite momenta before the system reaches the $\mathrm{Z}_2$ point from the lower density, even for $m_q$ smaller than the physical value. One of the possible implications of the appearance of such a tachyonic mode at finite momenta is that the assumed equilibrium state with a uniform chiral condensate is unstable toward a state with an inhomogeneous $\sigma$ condensate. No such anomalous behavior is found in the pseudoscalar channel. We find that the $\sigma$-to-$2\sigma$ coupling due to finite $m_q$ plays an essential role for the drastic modification of the spectral function.

Centralised submission by Collaboration Presenter name already specified
Content type Theory

Primary authors

Takeru Yokota (Kyoto University, Japan) Teiji Kunihiro (Kyoto University) Kenji Morita (Kyoto University)

Presentation Materials