Evidence for the unbinding of the 𝜙4 kink’s shape mode

The 𝜙4 double-well theory admits a kink solution, whose rich phenomenology is strongly affected by the existence of a single bound excitation called the shape mode. We find that the leading quantum correction to the energy needed to excite the shape mode is −0.115567λ/M in terms of the coupling λ/4 and the meson mass M evaluated at the minimum of the potential. On the other hand, the correction to the continuum threshold is −0.433λ/M. A naive extrapolation to finite coupling then suggests that the shape mode melts into the continuum at the modest coupling of λ/4 ∼ 0.106M2, where the ℤ2 symmetry is still broken.

A unified quark-nuclear matter equation of state from the cluster virial expansion within the generalized Beth–Uhlenbeck approach

We consider a cluster expansion for strongly correlated quark matter where the clusters are baryons with spectral properties that are described within the generalized Beth–Uhlenbeck approach by a medium dependent phase shift. We employ a simple ansatz for the phase shift which describes an on-shell bound state with an effective mass and models the continuum by an anti-bound state located at the mass of the three-quark continuum threshold, so that the Levinson theorem is fulfilled by construction. The quark and baryon interactions are accounted for by the coupling to scalar and vector meson mean fields modelled by density functionals. At increasing density and temperature, due to the different medium-dependence of quark and baryon masses, the Mott dissociation of baryons occurs and its contributions to the thermodynamics vanish. It is demonstrated on this simple example that this unified approach to quark-hadron matter is capable of describing crossover as well as first order phase transition behaviour in the phase diagram with a critical endpoint. Changing the meson mean field, the case of a “crossover all over” in the phase diagram is also obtained.

Bridging the two order parameters for the QCD deconfiment phase transition

We study the relation between two order parameters for deconfinement, normally employed in the literature: the continuum threshold s0, in the context of QCD Sum Rules, and the trace of the Polyakov loop ϕ in the framework of a nonlocal SU(2) chiral quark model. We establish a bridge between both order parameters at finite temperature T and baryonic chemical potential μ. In our analysis, we also include the the chiral quark condensate, the order parameter for the chiral symmetry restoration. We found that s0 and ϕ provide us with the same information for the deconfinement transition, both for the zero and finite chemical potential cases. At zero density, the critical temperatures for both quantities coincide exactly. This part of the analysis has been reinforced by the discussion of the corresponding susceptibilities and the static quark entropy behavior. At finite μ both order parameters provide evidence for the appearance of a quarkyonic phase.

Charm quark mass determined from a pair of sum rules

In this paper, we present preliminary results of the determination of the charm quark mass [Formula: see text] from QCD sum rules of moments of the vector current correlator calculated in perturbative QCD at [Formula: see text]. Self-consistency between two different sum rules allow to determine the continuum contribution to the moments without requiring experimental input, except for the charm resonances below the continuum threshold. The existing experimental data from the continuum region is used, then, to confront the theoretical determination and reassess the theoretic uncertainty.

Nature of the X(5568) — A critical Laplace sum rule analysis at N2LO

We scrutinize recent QCD spectral sum rules (QSSR) results to lowest order (LO) predicting the masses of the [Formula: see text] molecule and [Formula: see text] four-quark states. We improve these results by adding NLO and N2LO corrections to the PT contributions giving a more precise meaning on the [Formula: see text]-quark mass definition used in the analysis. We extract our optimal predictions using Laplace sum rule (LSR) within the standard stability criteria versus the changes of the external free parameters ([Formula: see text]-sum rule variable, [Formula: see text] continuum threshold and subtraction constant [Formula: see text]). The smallness of the higher order PT corrections justifies (a posteriori) the LO order results ⊕ the uses of the ambiguous heavy quark mass to that order. However, our predicted spectra in the range [Formula: see text] MeV, summarized in Table 7, for exotic hadrons built with four different flavors [Formula: see text], do not support some previous interpretations of the D0 candidate,1 [Formula: see text], as a pure molecule or a four-quark state. If experimentally confirmed, it could result from their mixing with an angle: [Formula: see text]. One can also scan the region [Formula: see text] MeV (where the [Formula: see text] might be a good candidate) and the one [Formula: see text] MeV for detecting these [Formula: see text] and [Formula: see text] unmixed exotic hadrons (if any) via, eventually, their radiative or [Formula: see text][Formula: see text]+[Formula: see text]hadrons decays.