The BMS (Bondi-van der Burg-Metzner-Sachs) symmetry arises as the asymptotic symmetry of flat spacetime at null infinity. In particular, the BMS algebra for three dimensional flat spacetime (BMS$_3$) is generated by the super-rotation generators which form a Virasoro sub-algebra with central charge $c_L$, together with mutually-commuting super-translation generators. The super-rotation and super-translation generators have non-trivial commutation relations with another central charge $c_M$.
We study a free scalar theory in two dimensions exhibiting BMS$_3$ symmetry, which can also be understood as the ultra-relativistic limit of a free scalar CFT$_2$. Upon canonical quantization on the highest weight vacuum, the central charges are found to be $c_L=2$ and $c_M=0$. Because of the vanishing central charge $c_M=0$, the theory features novel properties: there exist primary states which form a multiplet, and the Hilbert space can be organized by an enlarged version of BMS modules dubbed the staggered modules.
We further calculate correlation functions and the torus partition function, the later of which is also shown explicitly to be modular invariant.
Biography:
Peng-Xiang Hao got his Ph.D in physics from Peking University, supervised by Prof. Bin Chen. Now he is a postdoc in the Yau Mathematical Sciences Center, Tsinghua University, under the supervision of Prof. Wei Song. His main research interests include the holography beyond AdS/CFT correspondence and the non-Lorentz invariant field theories.
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