$U(1)\otimes BRST$ symmetry, of on-shell T-matrix elements and (1-$\varphi$-I) Green's functions, determines the vacuum state of the Abelian Higgs Model from symmetry alone: minimization of the scalar-sector effective potential is unnecessary

Abstract

The weak-scale $U(1{)}_Y$ Abelian Higgs Model (AHM) is the spontaneous-symmetry-breaking gauge theory of a complex scalar $\varphi =\frac{1}{\sqrt{2}}(H+i\pi )$ and a vector $A_{\mu }$. Global $U(1{)}_Y\otimes BRST$ symmetry emerges: when it is realized that on-shell T-matrix elements enjoy an extra $U(1{)}_Y$ global symmetry beyond the Lagragian's BRST symmetry. The symmetries co-exist: $U(1{)}_Y$ generators ${\delta }_{U(1{)}_Y}$ commute with BRST generators s and $[{\delta }_{U(1{)}_Y},s]\mathcal{L}=0$. Two towers of Ward Takahashi identities (WTI), which include all-loop-orders quantum corrections, emerge: a tower of relations among off-shell 1-$\varphi$-I (but 1-$A_{\mu }$-Reducible) Green's functions; another tower of Adler-zero WTI for on-shell T-matrix elements. The T-matrix's LSS theorem forces tadpoles to automatically vanish (equivalently $m_{\pi }^2=0$) by symmetry alone. We show that, when the full symmetries of Lorenz gauge AHM are enforced on the scalar-sector effective potential, the vacuum state of the theory is specified/decided by symmetry alone. We use recursive WTI relations among Green's functions to include opeators of dimension $\ge 1$. We express the fully renormalized scalar-sector effective potential in a form which shows explicitly that, for small scalar field values, the gauge-independent vacuum state of the theory $⟨H{⟩}_{renormalized}=Z_{\varphi }^{1/2}⟨H{⟩}_{bare}$ is determined by $U(1{)}_Y\otimes BRST$ symmetry alone, without minimizing the effective potential.

Comments: 15 pages, 1 appendix