Ricci-flat deformation of orbifolds and localized tachyonic modes

TL;DR

This paper investigates how Ricci-flat deformations affect orbifold models in type II string theory, deriving formulas for mass corrections of twisted modes, and analyzing the emergence of tachyonic states under various conditions.

Contribution

It provides a simple formula for mass corrections to twisted modes due to Ricci-flat deformations and applies it to both supersymmetric and nonsupersymmetric orbifolds, revealing conditions for tachyonic states.

Findings

Tachyonic states appear when supersymmetry is broken by deformations.

Mass corrections for certain states match solutions of wave equations in background geometries.

The unstable mode for N=1 is identified as the bubble creation tachyon.

Abstract

We study Ricci-flat deformations of orbifolds in type II theory. We obtain a simple formula for mass corrections to the twisted modes due to the deformations, and apply it to originally tachyonic and massless states in several examples. In the case of supersymmetric orbifolds, we find that tachyonic states appear when the deformation breaks all the supersymmetries. We also study nonsupersymmetric orbifolds C^2/Z_{2N(2N+1)}, which is T-dual to N type 0 NS5-branes. For N>=2, we compute mass corrections for states, which have string scale tachyonic masses. We find that the corrected masses coincide to ones obtained by solving the wave equation for the tachyon field in the smeared type 0 NS5-brane background geometry. For N=1, we show that the unstable mode representing the bubble creation is the unique tachyonic mode.