Holography at Work for Nuclear and Hadron Physics

Abstract

The purpose of this review is to provide basic ingredients of holographic QCD to nonexperts in string theory and to summarize its interesting achievements in nuclear and hadron physics. We focus on results from a less stringy bottom-up approach and review a stringy top-down model with some calculational details. 1 The approaches based on the Anti de Sitter/conformal field theory (AdS/CFT) correspondence [1-3] find many interesting possibilities to explore strongly interacting systems. The discovery of D-branes in string theory [4] was a crucial ingredient to put the correspondence on a firm footing. Typical examples of the strongly interacting systems are dense baryonic matter, stable/unstable nuclei, strongly interacting quark gluon plasma, and condensed matter systems. The morale is to introduce an additional space, which roughly corresponds to the energy scale of 4D boundary field theory, and try to construct a 5D holographic dual model that captures certain non-perturbative aspects of strongly coupled field theory, which are highly non-trivial to analyze in conventional quantum field theory based on perturbative techniques. There are in general two different routes to modeling holographic dual of quantum chromodynamics (QCD). One way is a top-down approach based on stringy D-brane configurations. The other way is so-called a bottom-up approach to a holographic, in which a 5D holographic dual is constructed from QCD. Despite the fact that this bottom-up approach is somewhat ad hoc, it reflects some important features of the gauge/gravity duality and is rather successful in describing properties of hadrons. However, we should keep in mind that a usual simple, tree-level analysis in the holographic dual model, both top-down and bottom-up, is capturing the leading N c contributions, and we are bound to suffer from sub-leading corrections.The goal of this review is twofold. First, we will assemble results mostly from simple bottomup models in nuclear and hadron physics. Surely we cannot have them all here. We will devote to selected physical quantities discussed in the bottom-up model. The selection of the topics is based on authors' personal bias. Second, we present some basic materials that might be useful to understand some aspects of AdS/CFT and D-brane models. We will focus on the role of the AdS/CFT in low energy QCD. Although the correspondence between QCD and gravity theory is not known, we can obtain much insights on QCD by the gauge/gravity duality.We organize this review as follows. Section 2 reviews the gauge/gravity. Section 3 briefly discuss developments of holographic QCD and demonstrates how to build up a bottom-up model using the AdS/CFT dictionary. After discussing the gauge/gravity duality and modeling in the bottom-up approach, we proceed with selected physical quantities. In each section, we show results mostly from the bottom-up approach and list some from the top-down model. Section 4 deals with vacuum condensates of QCD in holographic QCD. We will mainly discuss the gluon condensate and the...

Solitonic approach to holographic nuclear physics

“…Nuclear physics at low energy is thus turned into a multi-instanton problem in a curved five-dimensional background; this is the problem we discuss in the present paper. We will approach the problem of nuclei in the SS model from a "solitonic perspective", in a way somehow different, or complementary to other approaches which already exist in the literature [7][8][9][10][11][12][13][14]. We shall use many techniques developed in the context of nuclei within the Skyrme model, for example [15,16,[18][19][20][21][22][23][24].…”

Nucleon structure including high Fock states in AdS/QCD

“…[2]). One of the popular formalisms of this kind is the "soft-wall" model [3]- [24], which uses a soft infrared (IR) cutoff in the fifth dimension.…”

Tetraquarks in AdS/QCD

“…3 Anomalous dimensions of a qualitatively similar z dependence (in the region of interest) are encountered in dual backgrounds of holographic RG-flow type [14]. 4 Hence the phenomenological ratio Mq2 q 2 ,0 /Mq q,0 ∼ 0.8/1.5 is not quantitatively reproduced, perhaps due to the neglect of theqq interpolator's anomalous dimension.…”

“…Without guidance from the naive quark model, the theoretical analysis of such exotic states has to deal with the challenges of the strongly-coupled gauge dynamics more directly. Adding to the arsenal of suitable methods for this purpose (which now includes devoted lattice simulations [3]), the AdS/QCD approach [4] was recently extended to provide holographic insights into tetraquark properties [5].…”