Lysov Vyacheslav, Pasterski Sabrina, Strominger Andrew
Center for the Fundamental Laws of Nature, Harvard University, Cambridge, Massachusetts 02138, USA.
Phys Rev Lett. 2014 Sep 12;113(11):111601. doi: 10.1103/PhysRevLett.113.111601. Epub 2014 Sep 11.
It was shown by Low in the 1950s that the subleading terms of soft-photon S-matrix elements obey a universal linear relation. In this Letter, we give a new interpretation to this old relation, for the case of massless QED, as an infinitesimal symmetry of the S matrix. The symmetry is shown to be locally generated by a vector field on the conformal sphere at null infinity. Explicit expressions are constructed for the associated charges as integrals over null infinity and shown to generate the symmetry. These charges are local generalizations of electric and magnetic dipole charges.
20世纪50年代，洛证明了软光子S矩阵元的次主导项服从一个普遍的线性关系。在本信函中，对于无质量量子电动力学的情况，我们对这个旧关系给出一种新的解释，即将其视为S矩阵的无穷小对称性。该对称性由零无穷远处共形球面上的一个矢量场局部生成。构造了相关电荷作为零无穷远处积分的显式表达式，并证明其能生成该对称性。这些电荷是电偶极矩和磁偶极矩电荷的局部推广。
