Remarks on Decay of Defects with Internal Degrees of Freedom
We consider the examples of the chiral magnetic effect and the similar processes related to the decays of the extended objects in different theories. The examples involve the decay of an axion wall in an external magnetic field, pionic walls, metastable w
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Remarks on Decay of Defects with Internal Degrees of Freedom A. Gorsky
12.1 Introduction The chiral magnetic effect [1] seems to play an important role in the heave ions collision. The key question concerns the physical realization of the chiral chemical potential responsible for this phenomena. Usually it is attributed to the instanton effects however there are another sources for the effective chiral chemical potential In this paper we review three problems of such type: the decay of a metastable axion wall in an external magnetic field, the decay of walls in dense matter, and the decay of a nonabelian string with the excitation [2]. It is known that due to the one-loop Goldstone-Wilczek current [3] an axion wall in an external magnetic field develops a homogeneous density of the charged fermions [4–8]. The question we investigate here is whether the fermions stay localized on the remaining part of the domain wall during its decay or escape into the bulk? We find that in the leading approximation the fermions leave the domain wall and provide a very clear pattern of the chiral magnetic effect (CME) which currently attracts a considerable attention related to the observed charge separation effect at RHIC [1]. We shall thus argue that the decay of domain wall provides an effective chiral chemical potential responsible for the chiral magnetic effect. The second problem is related to the decay of mesonic walls in QCD. The nontrivial density of the Skyrmions is generated in the external magnetic field on π 0 walls, and the field prevents the wall from nonperturbative decay above some Bcrit [9]. There is a new point in the mesonic wall decay in dense matter. It is known [10] that in this case due to the anomalous term in the action the current is generated along the axion-like string at the boundary of the wall. In the decay problem the axion string is the boundary of the hole and therefore there is the circular boundary current during the decay. We analyze the impact of the created current on the magnetic field. A. Gorsky (B) Institute of Theoretical and Experimental Physics, Moscow 117259, Russia e-mail: [email protected] D. Kharzeev et al. (eds.), Strongly Interacting Matter in Magnetic Fields, Lecture Notes in Physics 871, DOI 10.1007/978-3-642-37305-3_12, © Springer-Verlag Berlin Heidelberg 2013
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A. Gorsky
The third problem in our discussion concerns the decay process of a nonabelian string with excited internal CPN degrees of freedom. The Lagrangian of the worldsheet theory supports a kink excitation [11–13] which can exist in isolation by itself in SUSY theories and as kink-antikink bound states in a generic non-SUSY case. We shall argue that in the nonabelian string decay the kink excitations on the string decrease the decay rate. The paper is organized as follows. In Sect. 12.2 we consider the process of the axion domain wall decay. The decays of mesonic walls in QCD are considered in Sect. 12.3. In Sect. 12.4 we comment on the decay of nonabelian string with the emphasis on the role of kink excitati
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