Tensionless Strings in a Kalb-Ramond Background

We investigate tensionless (or null) bosonic string theory with a constant Kalb-Ramond
background turned on. In analogy with the tensile case, we find that the constant Kalb-Ramond field
has a non-trivial effect on the spectrum only when the theory is compactified on an S^1 ⊗d
background with d ≥ 2. We discuss the effect of this constant background field on the tensionless
spectrum constructed on three known consistent null string vacua. We elucidate further
on the intriguing fate of duality symmetries in these classes of string theories when the
background field is turned on. Based on: https://arxiv.org/abs/2404.01385