Layers of deformed instantons in holographic baryonic matter

Abstract

We discuss homogeneous baryonic matter in the decompactified limit of the Sakai-Sugimoto model, improving existing approximations based on flat-space instantons. We allow for an anisotropic deformation of the instantons in the holographic and spatial directions and for a density-dependent distribution of arbitrarily many instanton layers in the bulk. Within our approximation, the baryon onset turns out to be a second-order phase transition, at odds with nature, and there is no transition to quark matter at high densities, at odds with expectations from QCD. This changes when we impose certain constraints on the shape of single instantons, motivated by known features of holographic baryons in the vacuum. Then, a first-order baryon onset and chiral restoration at high density are possible, and at sufficiently large densities two instanton layers are formed dynamically. Our results are a further step towards describing realistic, strongly interacting matter over a large density regime within a single model, desirable for studies of compact stars.

Towards a holographic quark-hadron continuity

“…The study most relevant to the present paper is Ref. [58], whose notation we shall employ. Here we will not go into details regarding the construction of the model itself and refer the reader to the reviews and original works quoted in the introduction and, more specifically, to Refs.…”

“…For simplicity, we shall later work with the ordinary trace. This is a tremendous simplification, and it has been shown for a very similar calculation that the use of the symmetrized trace prescription does not make a large quantitative difference in the results [58]. The expression in the square root is obtained from det(g + 2πα F), where g is the induced metric on the flavor branes, F is the field strength tensor, and α = 2 s with the string length s (which is absorbed in the definition of the dimensionless field strengths).…”

“…For the explicit form of the metric see for instance Ref. [58]. It contains the temperature-dependent function…”

Heavy holographic QCD

“…Here and throughout the paper we work with the same dimensionless quantities used before in a series of works [15,35,36]. The relation to their dimensionful counterparts involves powers of M KK and the curvature radius R as well as some numerical constants, see for instance Table I…”

Baryon superfluids in AdS/CFT with flavor

“…In order to describe baryonic matter one needs to study multi-soliton solutions [16][17][18][19] or use a phenomenological approach if one is interested in homogeneous states [20][21][22][23][24][25][26][27][28][29], with the drawback that the physical properties of the state depends on the assumptions one needs to make. Furthermore, stable soliton solutions have sizes that are typically of the order of the string scale [14], thus casting doubts on the validity of the brane action used to find those solutions.…”