Journal Club

Seminar Room

Tuesday 6th of October, 2026

Hour: 11:00

Title: Standard Model Effective Field Theory and Oscillons

Presented by: Luis Gil Martín

Ref: https://arxiv.org/abs/2607.23616

Abstract:

We show that the inclusion of a dimension-six operator in the Higgs potential has a dramatic impact on the stability of oscillons in the SU(2) bosonic sector of the Standard Model, extending their lifetime by orders of magnitude. This happens for the physical value of the ratio between the Higgs and W boson masses, mH/mW=1.556 and for the dimension-six operator O6=(Φ†Φ)3 whose coupling constant is below the current upper bound.

Hour: 11:30

Title: Tracing out massive fields in cosmology

Presented by: Andrea Sanfilippo

Ref: https://arxiv.org/pdf/2609.30370

Abstract:

Cosmological correlators are calculated through the in-in formalism in (quasi-)de Sitter
background. Its effective description is best represented by a reduced density matrix. In this work,
we study how integrating out a massive field in de Sitter space determines the reduced density matrix
of a light field at a finite observation time. Starting from a quasi-single-field model with non-linear
couplings, we first evaluate the massive field wavefunctional at fixed final value and then trace over
this value. The trace generates branch-mixing terms which are generally present in the Schwinger–
Keldysh description. For a conformally coupled massive field, we show explicitly that the light
field bispectrum from the effective description agrees with a full theory calculation. This example
also shows that decay of a field at the future boundary does not by itself justify discarding its
contribution to the trace. We discuss the differences between an exact nonlocal effective description
and the local effective field theory obtained through a large mass expansion. We then identify which
local cubic terms affect the late-time probability and which contribute only a wavefunctional phase.
Finally, we organize the resulting kernels by response, noise, and Schwinger–Keldysh consistency
conditions, and discuss the symmetry constraints on the reduced density matrix.