Date&Time  Wed Feb 10 2021 (13:30  14:30) 

Speaker  Yu Hamada 
Affiliation  Kyoto Univ. 
Title  Gravitational instantons and anomalous chiral symmetry breaking 
Abstract  We study anomalous chiral symmetry breaking in twoflavour QCD induced by gravitational and QCDinstantons within asymptotically safe gravity within the functional renormalisation group approach. Similarly to QCDinstantons, gravitational ones, associated to a K3surface connected by a wormholelike throat in flat spacetime, generate contributions to the "t Hooft coupling proportional to exp(1/gN) with the dimensionless Newton coupling gN. Hence, in the asymptotically safe gravity scenario with a nonvanishing fixed point coupling gN*, the induced "t Hooft coupling is finite at the Planck scale, and its size depends on the UV theory. Within this scenario the gravitational effects on anomalous U(1)Abreaking at the Planck scale could survive at low energy scales. In turn, fermion masses of the order of the Planck scale are inconsistent with observations. This constrains the allowed asymptotically safe UVcompletion of the GravityQCD system. We mapout the parameter regime that is compatible with the existence of light fermions in the lowenergy regime. 
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