Identifying the breakdown of unbiased exponential resummation in lattice QCD at a finite isospin chemical potential

by Mr Sabarnya Mitra (Indian Institute of Science, Bengaluru)

Thursday 20 Apr 2023, 14:30 → 15:30 Asia/Kolkata

AG 69 and on zoom

Please contact rishi(at)theory(dot)tifr(dot)res(dot)in for the zoom meeting id and the password for this seminar.

The finite temperature calculations of unbiased exponential resummation at a real, finite isospin chemical potential $\mu_I$ in lattice QCD do not experience the fermion sign problem. Although this suggests that the computations, in principle can be continued for all real finite values of $\muI$ however recent studies demonstrating the formation of a pion condensate in the isospin phase diagram of QCD at a finite temperature $T$ possibly imply the occurrence of a breakdown of this formalism at some finite value of $\muI$. We present results illustrating the singularities of the partition function obtained using the Newton-Raphson method in complex $\muI$ plane. We observe a naive non-monotonic behavior of isospin number density beyond the radius of convergence which is determined by the Newton-Raphson singularity situated closest to the origin. We also introduce a new way of formulating a non-trivial phasefactor in complex $\mu_I$ which seems to identify reliably the onset of this breakdown along the real $\muI$ axis. We also illuminate increasing severity of the overlap problem with increasing value of physical $\mu_I$. We find that the relative error bars of kurtosis as a measure of this overlap problem become significantly large on going beyond the value of real $\muI$ from which, these average phasefactor values start becoming zero.