Abstract
Baryonic states are sufficiently complex to reveal physics that is hidden in the mesonic bound states. Using gauge/gravity correspondence we study analytically and numerically baryons in theories with space-dependent $\theta$-term, or theories under strong magnetic fields. Such holographic studies on baryons are accommodated in a generic analytic framework we develop for anisotropic theories, where their qualitative features are common irrespective of the source that triggers the anisotropy. We find that the distribution of the quarks forming the state, depends on the angle between the baryon and the anisotropic direction. Its shape is increasingly elliptic with respect to the strength of the field sourcing the anisotropy, counterbalancing the broken rotational invariance on the gluonic degrees of freedom. Strikingly, the baryons dissociate in stages with a process that depends on the proximity of the quarks to the anisotropic direction, where certain quark pairs abandon the bound state first, followed by the closest pairs to them as the temperature increases. This observation may also serve as a way to identify the nature of certain exotic states. Finally, we investigate holographic baryons with decreased number of quarks and explain why in theories under consideration the presence of anisotropy does not modify the universal stability condition in contrast to the usual trend.
Highlights
The early quarkonium studies were based on the nonrelativistic potentials [1,2], while the present formulation is in the context of the effective field theories of QCD, lattice-QCD [3,4,5,6] and of the gauge/gravity duality [7,8] where the focus is mostly on qualitative but still insightful physics
Baryons may be relatively simple but are sufficiently complex to reveal physics hidden in the mesonic bound states, making them worthy to study
We have provided a generic formalism for the study of holographic baryons in strongly coupled anisotropic theories
Summary
Quarkonium physics is fundamental to reveal properties of the QCD and its dynamics. The early quarkonium studies were based on the nonrelativistic potentials [1,2], while the present formulation is in the context of the effective field theories of QCD, lattice-QCD [3,4,5,6] and of the gauge/gravity duality [7,8] where the focus is mostly on qualitative but still insightful physics. The fundamental question is whether or not there exists a unique physical picture sufficient to explain all the new experimental data on production mechanisms, masses, decay modes and rates, capable of identifying the exact type of the bound state observed from the options listed above. In the presence of a magnetic field in QCD, several peculiar phenomena appear when anisotropies are present [23,24] What makes such studies even more interesting from the point of view of holography, is that most observables and phenomena depend mostly on the fact that the anisotropies are present, irrespective of the source triggering them. The derivation of such confining theories and their phase transitions has been done recently [30] opening the window for further studies in the confined region
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