Classifying bions in Grassmann sigma models and non-Abelian gauge theories by D-branes
Abstract
We classify bions in the Grassmann Gr_{N_F,N_C} sigma model (including the {C}P^{N_F-1} model) on {R}1× S1 with twisted boundary conditions. We formulate these models as U(N_C) gauge theories with N_F flavors in the fundamental representations. These theories can be promoted to supersymmetric gauge theories and, further, can be embedded into D-brane configurations in type-II superstring theories. We focus on specific configurations composed of multiple fractional instantons, termed neutral bions and charged bions, which are identified as perturbative infrared renormalons by Ünsal and his collaborators [G. V. Dunne and M. Ünsal, J. High Energy Phys. 1211, 170 (2012); G. V. Dunne and M. Ünsal, Phys. Rev. D 87, 025015 (2013)]. We show that D-brane configurations, as well as the moduli matrix, offer a very useful tool to classify all possible bion configurations in these models. In contrast to the {C}P^{N_F-1} model, there exist Bogomol'nyi-Prasad-Sommerfield (BPS) fractional instantons with topological charges greater than unity (of order N_C) that cannot be reduced to a composite of an instanton and fractional instantons. As a consequence, we find that the Grassmann sigma model admits neutral bions made of BPS and anti-BPS fractional instantons, each of which has a topological charge greater (less) than one (minus one), that are not decomposable into an instanton-anti-instanton pair and the rest. The {C}P^{N_F-1} model is found to have no charged bions. In contrast, we find that the Grassmann sigma model admits charged bions, for which we construct exact non-BPS solutions of the field equations.
- Publication:
-
Progress of Theoretical and Experimental Physics
- Pub Date:
- March 2015
- DOI:
- 10.1093/ptep/ptv009
- arXiv:
- arXiv:1409.3444
- Bibcode:
- 2015PTEP.2015c3B02M
- Keywords:
-
- B23;
- B34;
- B35;
- B37;
- High Energy Physics - Theory;
- High Energy Physics - Phenomenology
- E-Print:
- 62 pages, 37 figures