Interference effects in new physics searches

TL;DR

The paper addresses how interference between new scalar resonances and SM backgrounds or other resonances can substantially alter observable distributions in searches for extended scalar sectors. It analyzes the theoretical framework of finite-width and interference effects, including limitations of the narrow width approximation, and emphasizes that full amplitudes with interference must be considered on a case-by-case basis. By reviewing real singlet extensions and Two Higgs Doublet Models, it demonstrates how interference reshapes diboson, di-Higgs, triple-Higgs, and difermion final states, often invalidating Breit-Wigner-only expectations and affecting experimental reach. The work advocates using LO tools that incorporate interference, discusses possible pathways to include higher-order corrections, and calls on experiments to integrate these effects into analyses to obtain correct distributions and robust constraints.

Abstract

Interference effects are an important consequence of a correct description in physics theories within and beyond the Standard Model (SM) of particle physics. However, many current theoretical descriptions as well as experimental searches neglect such effects, which can, among others, lead to an incorrect description of e.g. kinematical distributions, at least within the context of UV-complete models. In this review, I briefly discuss the current status and most common descriptions as well as existing studies of such effects, where I focus on models with extended scalar searches.

Figures (10)

• Figure 1: Invariant di-boson mass distributions for a scenario where $p\,p\,\rightarrow\,H\,\rightarrow\,V\,V$ is the target signature. $S$ denotes the contribution from the target process, $I_{h1/bkg}$ are contributions from interference with the SM scalar, denote by $h1$, and the continuum background, respectively. Displayed is the signal-only distribution (in black), signal including interference from the 125 $$ GeV resonance (in red), as well as complete contribution where all interference terms are taken into account (in blue). The pure SM background is subtracted. Figure is taken from Kauer:2015hia. See text and original reference for further details.
• Figure 2: Invariant mass distribution in the $W^+W^-$ final state for a heavy resonance of 3 $$ TeV: signal only (red) as well as signal including interference with the continuum background (green). Figure is taken from Kauer:2019qei.
• Figure 3: Invariant mass distributions for the diboson system in a 2HDM with parameters as specified in the caption, for various width assumptions. It is clear that the resonance only distribution does not give the full picture. We also see a clear modification when the width is varied. Taken from Jung:2015sna.
• Figure 4: Figure highlightening the effects of including interference contributions. Left: Different contributions for a fixed new physics scenario, both in the full mass dependence and heavy top limit. Right: Total invariant mass distribution including interference effects for various new physics scenarios. Figures are taken from Dawson:2015haa.
• Figure 5: Invariant mass distributions for different benchmark scenarios for resonance enhanced di-Higgs production. Left: Prior to and right after taking smearing effects into account, resulting from finite detector resolution. Displayed are the pure resonances (green), SM background and resonance contribution with (red) and without (pink) correct coupling rescalings of the latter, as well as full contribution including all interference terms (blue). Figures are taken from Feuerstake:2024uxs and include K-factors that normalize to the total production cross sections at next-to-leading order (NLO) (see original reference for details).