Origin Of Electroweak Symmetry Breaking Research Articles

Electroweak scattering at the muon shot

It has long been recognized that the scattering of electroweak particles at very high energies is dominated by vector boson fusion, which probes the origin of electroweak symmetry breaking and offers a unique window into the ultraviolet regime of the Standard Model (SM). Previous studies assume SM-like couplings and rely on the effective W approximation (or electroweak parton distribution), whose validity is well established within the SM but not yet studied in the presence of anomalous Higgs couplings. In this work, we critically examine the electroweak production of two Higgs bosons in the presence of anomalous VVh and VVhh couplings. We compute the corresponding helicity amplitudes and compare the cross section results in the effective W approximation with the full fixed-order calculation. In particular, we identify two distinct classes of anomalous Higgs couplings, whose effects are not captured by vector boson fusion and effective W approximation. Such very-high-energy electroweak scatterings can be probed at the muon shot, a multi-TeV muon collider upon which we base our study, although similar considerations apply to other high-energy colliders. Published by the American Physical Society 2024

Vacuum stability and radiative symmetry breaking of the scale-invariant singlet extension of type II seesaw model

The questions of the origin of electroweak symmetry breaking and neutrino mass are two major puzzles in particle physics. Neutrino mass generation requires new physics beyond the Standard Model and also suggests reconsideration of physics of symmetry breaking. The aim of this paper is to study radiative symmetry breaking in the singlet scalar extension of type II seesaw neutrino mass model. We derive bounded-from-below conditions for the scalar potential of the model in full generality for the first time. The Gildener–Weinberg approach is utilised in minimising the multiscalar potential. Upon imposing the bounded-from-below and perturbativity conditions, as well as experimental constraints from colliders, we find the parameter space of scalar quartic couplings that can radiatively realise electroweak symmetry breaking at one-loop level. To satisfy all the constraints, the masses of the heavy triplet-like Higgs bosons must be nearly degenerate. The evolution of the Higgs doublet quartic coupling lambda _{H} can be prevented from being negative up to the Planck scale.

Strongly coupled gauge theories: What can lattice calculations teach us?

The dynamical origin of electroweak symmetry breaking is an open question with many possible theoretical explanations. Strongly coupled systems predicting the Higgs boson as a bound state of a new gauge-fermion interaction form one class of candidate models. Due to increased statistics, LHC run II will further constrain the phenomenologically viable models in the near future. In the meanwhile it is important to understand the general properties and specific features of the different competing models. In this work we discuss many-flavor gauge-fermion systems that contain both massless (light) and massive fermions. The former provide Goldstone bosons and trigger electroweak symmetry breaking, while the latter indirectly influence the infrared dynamics. Numerical results reveal that such systems can exhibit a light [Formula: see text] isosinglet scalar, well separated from the rest of the spectrum. Further, when we set the scale via the vev of electroweak symmetry breaking, we predict a 2 TeV vector resonance which could be a generic feature of SU(3) gauge theories.

20pAL-12 The origin of electroweak symmetry breaking via bosonic see-saw mechanism

20pAL-12 The origin of electroweak symmetry breaking via bosonic see-saw mechanism

Higgs pair production at the LHC and ILC from a general potential

Higgs cubic coupling plays a crucial role in probing an origin of electroweak symmetry breaking. It is expected that the cubic coupling is measured by Higgs pair production at the LHC and ILC, and the deviations from the standard model can be extracted from the Higgs pair production process, and those can give us a hint of new physics beyond the standard model. We consider a general potential that achieves the suitable electroweak symmetry breaking. As one of the interesting models, we suggest a nonperturbative Higgs model in which a runaway type of potential is used. In the model, the cross sections of pair production at the LHC are enlarged compared to the standard model. We also study the Higgs pair production induced by a noncanonical kinetic term of Higgs fields which will be important for searching the pair production at the ILC.

Formula omitted] and [formula omitted] feasibility studies with ATLAS at the LHC

The discovery of the origin of electroweak symmetry breaking, realized in the Standard Model and in some models beyond this theory by the Higgs mechanism, is one of the main goals of the ATLAS experiment at the Large Hadron Collider. This mechanism predicts the existence of one or more scalar particles, the Higgs boson(s). Higgs boson decay modes to tau leptons, such as H → τ + τ − , are very important as they could play a crucial role in searches within the challenging 120 – 140 GeV mass region. This channel is also important in supersymmetric extensions of the Standard Model through the associated production of the Higgs bosons with heavy quarks or by gluon fusion. Finally, the observation of a charged Higgs boson would constitute irrefutable evidence for physics beyond the Standard Model. A light charged Higgs boson would be produced in top quark decays through t → b H + , and would be likely to decay to a tau lepton and a neutrino. This paper summarizes recent ATLAS studies focusing on the above channels and concentrates on several experimental aspects of these analyses.

Composite Higgs boson pair production at the LHC

The measurement of the trilinear and quartic Higgs self-couplings is necessary for the reconstruction of the Higgs potential. This way the Higgs mechanism as the origin of electroweak symmetry breaking can be tested. The couplings are accessible in multi-Higgs production processes at the LHC. In this paper we investigate the prospects of measuring the trilinear Higgs coupling in composite Higgs models. In these models, the Higgs boson emerges as a pseudo-Goldstone boson of a strongly interacting sector, and the Higgs potential is generated by loops of the Standard Model (SM) gauge bosons and fermions. The Higgs self-couplings are modified compared to the SM and controlled by the compositeness parameter $\xi$ in addition to the Higgs boson mass. We construct areas of sensitivity to the trilinear Higgs coupling in the relevant parameter space for various final states.

Evidence for the multiverse in the standard model and beyond

In any theory it is unnatural if the observed values of parameters lie very close to special values that determine the existence of complex structures necessary for observers. A naturalness probability $P$ is introduced to numerically evaluate the degree of unnaturalness. If $P$ is very small in all known theories, corresponding to a high degree of fine-tuning, then there is an observer naturalness problem. In addition to the well-known case of the cosmological constant, we argue that nuclear stability and electroweak symmetry breaking represent significant observer naturalness problems. The naturalness probability associated with nuclear stability depends on the theory of flavor, but for all known theories is conservatively estimated as ${P}_{\mathrm{nuc}}\ensuremath{\lesssim}({10}^{\ensuremath{-}3}--{10}^{\ensuremath{-}2})$, and for simple theories of electroweak symmetry breaking ${P}_{\mathrm{EWSB}}\ensuremath{\lesssim}({10}^{\ensuremath{-}2}--{10}^{\ensuremath{-}1})$. This pattern of unnaturalness in three different arenas, cosmology, nuclear physics, and electroweak symmetry breaking, provides evidence for the multiverse, since each problem may be easily solved by environmental selection. In the nuclear case the problem is largely solved even if the multiverse distribution for the relevant parameters is relatively flat. With somewhat strongly varying distributions, it is possible to understand both the close proximity to neutron stability and the values of ${m}_{e}$ and ${m}_{d}\ensuremath{-}{m}_{u}$ in terms of the electromagnetic mass difference between the proton and neutron, ${\ensuremath{\delta}}_{\mathrm{EM}}\ensuremath{\simeq}1\ifmmode\pm\else\textpm\fi{}0.5\text{ }\text{ }\mathrm{MeV}$. It is reasonable that multiverse distributions are strong functions of Lagrangian parameters, since they depend not only on the landscape of vacua, but also on the population mechanism, ``integrating out'' other parameters, and on a density of observers factor. In any theory with mass scale $M$ that is the origin of electroweak symmetry breaking, strongly varying multiverse distributions typically lead either to a little hierarchy $v/M\ensuremath{\approx}({10}^{\ensuremath{-}2}--{10}^{\ensuremath{-}1})$, or to a large hierarchy $v\ensuremath{\ll}M$. In certain multiverses, where electroweak symmetry breaking occurs only if $M$ is below some critical value, we find that a little hierarchy develops with the value of ${v}^{2}/{M}^{2}$ suppressed by an extra loop factor, as well as by the strength of the distribution. Since the correct theory of electroweak symmetry breaking is unknown, our estimate for ${P}_{\mathrm{EWSB}}$ is theoretical. The LHC will lead to a much more robust determination of ${P}_{\mathrm{EWSB}}$, and, depending on which theory is indicated by the data, the observer naturalness problem of electroweak symmetry breaking may be removed or strengthened. For each of the three arenas, the discovery of a natural theory would eliminate the evidence for the multiverse; but in the absence of such a theory, the multiverse provides a provisional understanding of the data.

Trilepton Higgs boson signal at hadron colliders

Determining the origin of electroweak symmetry breaking will be one of the primary functions of high energy colliders. We point out that most Higgs boson searches pursued at hadron colliders require Yukawa interactions either in the production or the decay of a Higgs boson. We propose a trilepton Higgs boson search based only upon the gauge interactions of the Higgs. This strategy can be utilized successfully for the standard model (SM) Higgs boson as well as non-standard Higgs bosons which break electroweak symmetry but have little to do with fermion mass generation. The trileptons come from Wh production followed by Wh -> WWW^(*) -> 3l decays. A SM Higgs trilepton signal would be difficult to detect at the Tevatron collider: with 100 fb^{-1} of data, only a $3\sigma$ signal above background can be achieved after cuts if 140 GeV < mh < 175 GeV. Some discrimination of signal over background can be gained by analyzing the opposite sign dilepton pT distributions. At the LHC with 30 (100) fb^{-1} a clear discovery above the $5\sigma$ level is possible for a Higgs mass in the range 140-185 (125-200) GeV. Prospects for a trilepton Higgs discovery are greatly improved for models with non-standard Higgs sectors where a Higgs boson couples preferentially to vector bosons rather than to fermions.