Samanta Saha (CWRU)

Date: Tue. October 6th, 2026, 11:30 am-12:30 pm
Location: Foldy room
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The Many Faces of Nonlinearly Realized Spacetime Symmetries in EFTs

Abstract: Effective field theories organize low-energy physics in terms of the relevant degrees of freedom and their symmetries. A central expectation is that specifying the symmetry-breaking pattern determines the allowed interactions. For spontaneously broken spacetime symmetries, however, this expectation becomes subtle: apparently different geometric constructions can realize the same symmetry structure. In this talk, I will explore these subtleties through scalar EFTs with different geometric origins. Despite their different descriptions, these theories are related by an invertible field redefinition and have identical scattering amplitudes. This illustrates how physical observables distinguish genuine differences between theories from differences in their descriptions.

I will then turn to a complementary question: can observables reveal symmetries that are hidden in the original field description? In certain scalar theories in two-dimensional de Sitter space, correlators of shift-invariant operators reveal a hidden conformal symmetry. This raises the question of how the symmetry is realized on the underlying scalar field. I will discuss recent work on generalized chiral scalars in two-dimensional flat spacetime and their connection to these de Sitter theories, providing a new perspective on the origin and realization of this hidden conformal symmetry.