K-theory in cutoff version of Vacuum String Field Theory

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Solutions of the Vacuum String Field Theory (VSFT) equation of motion involving matter part are given by projectors, and they represent nonperturbative solutions (e.g. the sliver) interpreted as D25-branes (or lower dimensional branes), but they are not mathematically well defined as they have zero norm. In this work we will use a regularization procedure based on the cutoff version of Moyal String Field Theory (MSFT), a particular version of VSFT, and we will see that both the sliver and the butterfly states, in this regime, have a good mathematical description. In particular they are exponential functions belonging to $\Sc(\RR^{2Nd})$, the space of Schwartzian functions equipped with the *-product. Then we prove that if we classify those regularized solutions with K-theory group built out of the C*-algebra $\bar{\Sc}(\RR^{2Nd})$ we find exactly the same result obtained considering a K-theoretic classification of D25-branes in usual string theory, using the topological K-theory of vector bundles over the D25-brane worldvolume. We then comment on the meaning of this result and possible physical implications.