English

On a theorem of Narasimhan and Ramanan on deformations

Algebraic Geometry 2026-03-25 v2

Abstract

Let XX be a smooth projective curve genus GG (as elaborated in \ref{main1}), over an algebraically closed field kk of arbitrary characteristics. Let \cH\cH {\em be a tamely ramified absolutely simple, simply connected connected group scheme (see \eqref{quasisplitcase})}. Let \cM\cM denote the moduli stack \cMX(\cH)\cM_X(\cH) of \cH\cH-torsors on XX and \cMs\cM^{^s} be the open substack of {\em stable torsors}. Using the theory of parahoric torsors and Parahoric-correspondences, we describe the cohomology groups Hi(\cMs,\cT\cM),i=0,1,2\text{H}^i\left(\cM^{^s}, \cT_{_{\cM}}\right), i = 0,1,2 and Hi(\cMs,Ω\cM),i=0,1,2\text{H}^i\left(\cM^{^s}, \Omega_{_{\cM}}\right), i = 0,1,2 in terms of the curve XX. The classical results of Narasimhan and Ramanan are derived as a consequence.

Keywords

Cite

@article{arxiv.2506.17574,
  title  = {On a theorem of Narasimhan and Ramanan on deformations},
  author = {V. Balaji and Y. Pandey},
  journal= {arXiv preprint arXiv:2506.17574},
  year   = {2026}
}

Comments

Several typos and expository changes made. The results are more precise