Published for SISSA by Springer Received: November 27, 2020 Accepted: February 17, 2021 Published: March 22, 2021 RP4 From N = 4 Super-Yang-Mills on to bosonic JHEP03(2021)203 Yang-Mills on RP2 Yifan Wang Center of Mathematical Sciences and Applications, Harvard University, Cambridge, MA 02138, U.S.A. Jefferson Physical Laboratory, Harvard University, Cambridge, MA 02138, U.S.A. E-mail:
[email protected] Abstract: We study the four-dimensional N = 4 super-Yang-Mills (SYM) theory on the unorientable spacetime manifold RP4. Using supersymmetric localization, we find that for a large class of local and extended SYM observables preserving a common supercharge Q, their expectation values are captured by an effective two-dimensional bosonic Yang- Mills (YM) theory on an RP2 submanifold. This paves the way for understanding N = 4 SYM on RP4 using known results of YM on RP2. As an illustration, we derive a matrix integral form of the SYM partition function on RP4 which, when decomposed into discrete holonomy sectors, contains subtle phase factors due to the nontrivial η-invariant of the Dirac operator on RP4. We also comment on potential applications of our setup for AGT correspondence, integrability and bulk-reconstruction in AdS/CFT that involve cross-cap states on the boundary. Keywords: Conformal Field Theory, Supersymmetric Gauge Theory ArXiv ePrint: 2005.07197 Open Access, c The Authors. https://doi.org/10.1007/JHEP03(2021)203 Article funded by SCOAP3. Contents 1 Introduction1 2 Localization of the N = 4 SYM on RP4 3 2.1 The SYM on RP4 from involution3 2.2 The supersymmetric action for N = 4 SYM on RP4 6 2.3 Localization to 2d YM on RP2 7 JHEP03(2021)203 3 2d YM on RP2 and a new matrix model9 3.1 Partition function 10 3.2 Discrete holonomy sectors and phase factors 13 4 Conclusion and discussion 15 1 Introduction Quantum field theories with time reversal symmetry can be formulated on unorientable spacetime manifolds.