We study scaling behavior of a chiral order parameter in the low density region, performing a simulation of two-flavor QCD with improved Wilson quarks. The scaling behavior of the chiral order parameter defined by a Ward-Takahashi identity agrees with the scaling function of the three-dimensional O(4) spin model at zero chemical potential. We extend the scaling study to finite density QCD. Applying the reweighting method and calculating derivatives of the chiral order parameter with respect to the chemical potential, the scaling properties of the chiral phase transition are discussed in the low density region. We moreover calculate the curvature of the phase boundary of the chiral phase transition in the temperature and chemical potential plane assuming the O(4) scaling relation.

This work is in part supported by Grants-in-Aid of the Japanese Ministry of Education, Culture, Sports, Science and Technology (Nos. 21340049, 22740168, and 23540295) and by the Large Scale Simulation Program No.12/13-14 (FY2012-2013) of High Energy Accelerator Research Organization (KEK). SY is supported by JSPS Strategic Young Researcher Overseas Visits Program for Accelerating Brain Circulation (No. R2411). HS is also supported by JSPS for Young Scientists.

The 31st International Symposium on Lattice Field Theory (LATTICE 2013) ; Place : Mainz, Germany ; Date : 29 July - 3 August, 2013