Gravity as a gapless phase and biform symmetries

Abstract

We study effective field theories (EFTs) enjoying (maximal) biform symmetries. These are defined by the presence of a conserved (electric) current that has the symmetries of a Young tableau with two columns of equal length. When these theories also have a topological (magnetic) biform current, its conservation law is anomalous. We go on to show that this mixed anomaly uniquely fixes the two-point function between the electric and magnetic currents. We then perform a Källén-Lehmann spectral decomposition of the current-current correlator, proving that there is a massless mode in the spectrum, whose masslessness is protected by the anomaly. Furthermore, the anomaly gives rise to a universal form of the EFT whose most relevant term-which resembles the linear Einstein action-dominates the infrared physics. As applications of this general formalism, we study the theories of a Galileon superfluid and linearized gravity. Thus, one can view the masslessness of the graviton as being protected by the anomalous biform symmetries. The associated EFT provides an organizing principle for gravity at low energies in terms of physical symmetries, and allows interactions consistent with linearized diffeomorphism invariance. These theories are not ultraviolet-complete-the relevant symmetries can be viewed as emergent-nor do they include the nonlinearities necessary to make them fully diffeomorphism invariant, so there is no contradiction with the expectation that quantum gravity cannot have any global symmetries.

Soft theorems for boosts and other time symmetries

“…One motivation for the study of soft theorems for boost-like symmetries comes from condensed matter physics. There is a sense in which gapless phases of matter can be classified according to how they nonlinearly realize spacetime symmetries [45][46][47][48][49][50][51][52][53][54][55][56]. At low energies, one expects much of the dynamics of these systems to be controlled by the Goldstone modes that nonlinearly realize these symmetries.…”

Pion dynamics in a soft-wall AdS-QCD model

“…Interestingly, even more exotic type of Goldstone modes have been discussed in holography such as type II/B NGMs [26,27], out-of-equilibrium NGMs [28] and NGMs of spontaneously broken higher-form symmetries [29,30]. The graviton itself has been recently identified as a Goldstone boson of an exotic biform symmetry [31].…”

Higher Flavor Symmetries in the Standard Model

“…Other recent work toward higher symmetries in particle physics models includes refs. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] with refs. [26][27][28][29][30][31][32][33][34][35][36] touching on aspects of the Standard Model structure.…”