Signatures of Moat Regimes in Heavy-Ion Collisions

Abstract

Heavy-ion collisions at small beam energies have the potential to reveal the rich phase structure of QCD at nonzero temperature and density. Among the possible phases are regimes which feature periodic modulations of the spatial structure, where the energy spectrum is shaped like a moat, with the minimum of the energy over a sphere at nonzero momentum. We argue that if the matter created in heavy-ion collisions traverses such a regime, it can produce a characteristic momentum dependence of particle number and their correlations. As an explicit example, we consider a quantum pion liquid phase to compute these quantities on the freeze-out surface. These results can serve as a first guideline for a systematic search of spatially modulated phases in heavy-ion collisions.

Inhomogeneous Phases in the Chirally Imbalanced 2 + 1-Dimensional Gross-Neveu Model and Their Absence in the Continuum Limit

“…The Dirac operator corresponded to a block-diagonal matrix with N t N 2 s blocks of size 4 × 4. Thus, the ln Det Q (4) [µ, µ 45 , σ] term in the effective action (27) could be computed quite efficiently by summing over N t N 2 s determinants of 4 × 4 matrices. Moreover, the effective action at given µ, µ 45 and T is a function of just a single variable σ; hence, it could be minimized numerically in a straightforward and rather cheap way to obtain the physically preferred value of the homogeneous condensate.…”

“…The minimization algorithm also found 2-dimensional modulations. These, however, corresponded exclusively to local minima of the effective action (27). An example is shown in the center of Figure 7.…”

“…Now, we discuss the minimization of the effective action (27) with respect to the condensate allowing arbitrary spatial modulations, i.e., arbitrary Fourier coefficients σ(p). We did this for selected parameters (µ, µ 45 , T) by carrying out several conjugate gradient minimizations, which differed in starting values for σ(p).…”

“…[24]. In recent works [25][26][27][28] it has been discussed that inhomogeneous phases might be related to so-called moat regimes, where the bosonic wave function renormalization Z is negative. Such a regime has been found in an FRG study of the phase diagram of quantum chromodynamics (QCD) [29].…”

How an $ω_0$ condensate can spike the speed of sound in cold quarkyonic matter

“…For the pressure, the quark contribution is no larger than ∼ 4 , so at nonzero temperature, the quark contribution is only commesurate with that from gluons, ∼ 2 4 , when ∼ 1/4 . This is the basic idea behind a quarkyonic regime at nonzero density, where the free energy is that of (interacting) quarks and gluons, but excitations near the Fermi surface are still confined [2][3][4][5][6][7][8][9].…”