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Abstract

The mass spectrum of the gluonium with J PC = 0 −− is examined in three bottom-up AdS/QCD models. The results are used to identify several production and decay modes useful for searching this state. Moreover, the properties of such glueball in a hot and dense quark medium are discussed.Keywords QCD Phenomenology · Glueball and nonstandard multi-quark/gluon states PACS 11.25.Tq · 11.10.Kk · 12.39.Mk IntroductionGlueballs, bound states of gluons arising from the non-Abelian nature of strong interactions, are an important testbed for non perturbative aspects of QCD. The main obstacle in their search is the mixing with quarkonia (qq) with the same quantum numbers. A promising strategy for their identification is to focus on exotic states whose J PC quantum numbers are unaccessible to quark-antiquark configurations. This is the case of several gluonia with negative C-parity, composed of an odd number of constituent gluons ("oddballs"), for which little theoretical information is available. In particular, for J PC = 0 −− , the mass predictions for the lightest state span the range from m 0 −− = 2.79 GeV in the flux-tube model [1], to m 0 −− ≈ 5.166 GeV in lattice QCD simulations [2]. Two stable 0 −− oddballs, with masses m 0 −− = 3.81 ± 0.12 GeV and m 0 −− = 4.33 ± 0.13 GeV, have been predicted by QCD sum rules [3].The mass spectrum of the J PC = 0 −− oddball can be computed in a framework inspired by the AdS/CFT correspondence. This duality conjecture relates a strongly coupled gauge theory in a four dimensional (4D) Minkowski space to a semiclassical gravity theory defined in a five dimensional (5D) anti-de Sitter (AdS) geometry times a 5D sphere [4]. In Poincaré coordinates, the line elementwith z the fifth holographic coordinate, describes the AdS bulk metric. The original formulation of gauge/gravity duality required the 4D theory to be conformal invariant. Holographic bottom-up models, constructed to reproduce QCD properties, break such a symmetry by introducing an infrared energy scale in the bulk; the J PC = 0 −− oddball mass spectrum can then be determined either in vacuum or in a quark bath at finite temperature and density. Such an approach complements the top-down methods applied to analyze, e.g., the scalar 0 ++ gluonium [5; 6].