On the phenomenology of sphaleron-induced processes at the LHC and beyond

Abstract

We investigate the phenomenological aspects of non-perturbative baryon-and lepton-number-violating processes at hadron colliders. Such processes, induced by instanton/sphaleron configurations of the electroweak gauge fields, are believed to play a crucial role in the generation of baryon asymmetry in the early Universe at finite temperature. On the other hand, at colliders (that represent the zero-temperature high-energy regime) the rate and observability of such processes are still under debate. Motivated by current theoretical considerations, we construct a modern event generator within the general-purpose Herwig Monte Carlo framework, that aims to capture the most relevant features of the dominant processes. We perform a detailed phenomenological analysis focussing on the Large Hadron Collider, at 13 TeV proton-proton centre-of-mass energy, a potential highenergy upgrade at 27 TeV and the proposed Future Circular Collider (FCC-hh) at 100 TeV. We derive constraints on the expected rates for various parametrisations of our model. We find that all three colliders are capable of providing meaningful information on the nature of instanton/sphaleron-induced processes at various energy scales.

Triggering Higgs vacuum decay

“…The possibile utility of this speculative discussion is illustrating how, even if the Higgs vacuum is unstable, a significant safety factor is built in fundamental physics. Similar considerations limit the possibility of producing solitonic configurations at the weak scale [56],…”

Double and multiple bangs at tau neutrino telescopes: A novel probe of sphalerons with cosmogenic neutrinos

“…Though two-particle collisions were thought to be suppressed by the "few-to-many" consideration [107][108][109][110][111][112][113][114][115][116][117], recent studies taking account of the sphaleron periodicity suggest counter results [118][119][120]. While this fundamental issue itself is still under debate, one can instead turn to the high-energy experimental frontiers for the answer [121][122][123][124][125][126][127][128].…”

“…Since the sphaleron process is approximately pointlike and spherically symmetric, its cross section should be ceiled by the s-wave unitarity requirement of the scattering matrix, i.e., σ unitarity = 16π/ŝ for √ ŝ > E sp [129]. For the phenomenological study, a reasonable choice of the cross section is σ = min{σ 0 , σ unitarity } [128,129], implying that the higher-order corrections should come to the rescue when the unitarity is saturated. The total neutrino-nucleon cross section can then be obtained by convolving the parton-level one with quark PDFs.…”

Large effects from small QCD instantons: making soft bombs at hadron colliders

“…The question whether manifestations of tunnelling processes in QFT can be directly observed in high-energy experiments was already raised in the 1990s in the context of the electro-weak theory [24][25][26][27][28][29][30][31][32][33][34][35]. Studies of collider phenomenology of electro-weak instantons were carried out in [36] and more recently in [37,38].…”