Abstract
In theories with a perturbatively massless 2-form (dual to an axion), a paradox may arise in the process of black hole evaporation. Schwarzschild black holes can support a non-trivial Wilson-line-type field, the integral of the 2-form around their horizon. After such an ‘axionic black hole’ evaporates, the Wilson line must be supported by the corresponding 3-form field strength in the region formerly occupied by the black hole. In the limit of small axion decay-constant f, the energy required for this field configuration is too large. Thus, energy cannot be conserved in the process of black hole evaporation. The natural resolution of this paradox is through the presence of light strings, which allow the black hole to “shed” its axionic hair sufficiently early. This gives rise to a new Weak-Gravity-type argument in the 2-form context: small coupling, in this case f , enforces the presence of light strings or a low cutoff. We also discuss how this argument may be modified in situations where the weak coupling regime is achieved in the low-energy effective theory through an appropriate gauging of a model with a vector field and two 2-forms.
Highlights
In theories with a perturbatively massless 2-form, a paradox may arise in the process of black hole evaporation
Schwarzschild black holes can support a non-trivial Wilson-line-type field, the integral of the 2-form around their horizon. After such an ‘axionic black hole’ evaporates, the Wilson line must be supported by the corresponding 3-form field strength in the region formerly occupied by the black hole
As we have discussed in the Introduction, a contradiction arises in the process of evaporation of axionic black holes in the absence of light strings
Summary
As we have discussed in the Introduction, a contradiction arises in the process of evaporation of axionic black holes in the absence of light strings. This implies a parametric upper bound on the tension of strings (for a given gauge coupling f ). As we have discussed in the Introduction, a contradiction arises in the process of evaporation of axionic black holes in the absence of light strings.. As we have discussed in the Introduction, a contradiction arises in the process of evaporation of axionic black holes in the absence of light strings.5 This implies a parametric upper bound on the tension of strings (for a given gauge coupling f ). In order to derive the parametric form of the bound, we need to make certain assumptions about the latest stages of the evaporation of axionic BHs. We consider two possibilities and derive the parametric form of the constraints that arise in each case
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