We use modern dimensionally-reduced effective field theory methods, with careful attention to scale hierarchies, to analyze and catalog the types of first-order electroweak phase transitions that are possible in the Standard Model Effective Field Theory (SMEFT). Our calculations lay the necessary groundwork to perform gauge invariant, properly resummed perturbative expansions, and therefore address many of the theoretical problems with phase transition calculations.

Sweden

Eliel Camargo-Molina

Rikard Enberg

Johan Löfgren

A catalog of first-order electroweak phase transitions in the Standard Model Effective Field Theory

We explain the ATOMKI anomaly with a very light $\textit{Z}$′ state that features non-anomalous and non-flavour-universal vector and axial-vector couplings to all leptons. This $\textit{Z}$′ comes from a theoretical framework with a spontaneously broken U(1)′ symmetry in addition to the Standard Model gauge group and is compliant with current measurements of the anomalous magnetic moments of the electron and the muon as well as beam dump experiments. The lepton flavour structure of this model allows for $\textit{Z}$′ couplings to all light neutrinos, suggesting the possibility of $\textit{Z}$′-mediated Non-Standard Interactions (NSIs) of neutrinos in matter, so that measurements of the strength parameters of the NSIs can constrain the value of the couplings. We use experimental constraints on NSIs of neutrinos using older TEXONO data and newer IceCube data. The IceCube data, in particular, strongly constrain the flavour universality of the leptonic vector current. The constraints enable us to define the region of parameter space of this theoretical scenario that can be pursued in further phenomenological analyses.

United Kingdom

Türkiye

Yaşar Hiçyılmaz

Stefano Moretti

Carlos Heros

Harri Waltari

Constraints on the $\textit{X}$17 boson from IceCube searches for non-standard interactions of neutrinos

A first-order Electroweak Phase Transition (EWPT) could explain the observed baryon-antibaryon asymmetry and its dynamics could yield a detectable gravitational wave signature, while the underlying physics would be within the reach of colliders. The Standard Model, however, predicts a crossover transition. We therefore study the EWPT in the Standard Model Effective Field Theory (SMEFT) including dimension-six operators. A first-order EWPT has previously been shown to be possible in the SMEFT. Phenomenology studies have focused on scenarios with a tree-level barrier between minima, which requires a negative Higgs quartic coupling and a new physics scale low enough to raise questions about the validity of the EFT approach. In this work we stress that a first-order EWPT is also possible when the barrier between minima is generated radiatively, the quartic coupling is positive, the scale of new physics is higher, and there is good agreement with experimental bounds. Our calculation is done in a consistent, gauge-invariant way, and we carefully analyze the scaling of parameters necessary to generate a barrier in the potential. We perform a global fit in the relevant parameter space and explicitly find the points with a first-order transition that agree with experimental data. We also briefly discuss the prospects for probing the allowed parameter space using di-Higgs production in colliders.

José Camargo-Molina

A new perspective on the electroweak phase transition in the Standard Model Effective Field Theory

In this paper, we investigate a natural extension of the Standard Model that involves varying coupling constants. This is a general expectation in any fundamental theory such as string theory, and there are good reasons for why new physics could appear at reachable energy scales. We investigate the collider phenomenology of models with varying gauge couplings where the variations are associated with real singlet scalar fields. We introduce three different heavy scalar fields that are responsible for the variations of the three gauge couplings of the Standard Model. This gives rise to many interesting collider signatures that we explore, resulting in exclusion limits based on the most recent LHC data, and predictions of the future discovery potential at the high-luminosity LHC.

Ulf Danielsson

Gunnar Ingelman

Tanumoy Mandal

Varying gauge couplings and collider phenomenology

The two-Higgs Doublet Model (2HDM) is the most minimal extension of the Standard Model (SM) containing extra Higgs doublet fields. Given the multiplicity of Higgs states in a 2HDM, its Higgs potential is significantly more involved than the SM one. Importantly, it contains a multitude of Higgs triple self-couplings, unlike the SM, which only has one. These interactions are key to understanding the phenomenology of the 2HDM, as they uniquely determine the form of the potential. Several studies analysing the prospects of measuring these couplings at the Large Hadron Collider (LHC) have found them to be quite low generally. However, such studies have largely concentrated on Higgs pair-production induced by gluon-gluon scattering, either via direct annihilation or followed by their splitting into b-(anti)quark pairs, which in turn annihilate leaving behind spectator b-(anti)quarks. Both of these channels are therefore governed by QCD dynamics. We compare here the yields of such channels to those initiated by (primarily) valence quarks, which involve Electro-Weak (EW) interactions only, for neutral multi-Higgs final states. We find that EW production can be dominant over QCD production for certain final state combinations. We also illustrate that charged final states, which can only be produced via EW modes, could serve as important probes of some $$H^\pm $$ <math><msup><mi>H</mi><mo>±</mo></msup></math>  triple couplings, that are inaccessible in QCD-induced processes, during Run 2 and 3 of the LHC. Our analysis covers regions of the parameter space of the Type-I 2HDM that have escaped the most up-to-date experimental constraints coming from EW precision data, LHC measurements of the 125 GeV Higgs boson properties, searches for additional Higgs states, and flavour physics.

William Klemm

South Korea

Rwanda

Shoaib Munir

Electroweak production of multiple (pseudo)scalars in the 2HDM

We study the collider phenomenology of a neutral gauge boson Z ′ arising in minimal but anomalous U(1) extensions of the Standard Model (SM). To retain gauge invariance of physical observables, we consider cancellation of gauge anomalies through the Green-Schwarz mechanism. We categorize a wide class of U(1) extensions in terms of the new U(1) charges of the left-handed quarks and leptons and the Higgs doublet. We derive constraints on some benchmark models using electroweak precision constraints and the latest 13 TeV LHC dilepton and dijet resonance search data. We calculate the decay rates of the exotic and rare one-loop Z ′ decays to ZZ and Z -photon modes, which are the unique signatures of our framework. If observed, these decays could hint at anomaly cancellation through the Green-Schwarz mechanism. We also discuss the possible observation of such signatures at the LHC and at future ILC colliders.

Andreas Ekstedt

India

Minimal anomalous U(1) theories and collider phenomenology

We analyse the phenomenological implications of a light Higgs boson, h , within the CP-conserving 2-Higgs Doublet Model (2HDM) Type-I, for the detection prospects of the charged HÂ± state at Run II of the Large Hadron Collider (LHC), assuming s=13 TeV as energy and O(100Â fbâ1) as luminosity. When sufficiently light, this h state can open up the bosonic decay channel HÂ±âWÂ±(â)h , which may have a branching ratio significantly exceeding those of the HÂ±âÏÎ½ and HÂ±âcs channels. We perform a broad scan of the 2HDM Type-I parameter space, assuming the heavier of the two CP-even Higgs bosons, H , to be the observed SM-like state with a mass near 125 GeV. Through these scans we highlight regions in which mHÂ±&lt;mt+mb that are still consistent with the most recent limits from experimental searches. We find in these regions that, when the HÂ±âWÂ±(â)h decay mode is the dominant one, the h can be highly fermiophobic, with a considerably large decay rate in the Î³Î³ channel. This can result in the total cross section of the Ï(ppâHÂ±hâWÂ±(â)+4Î³) process reaching up to O(100Â fb) . We therefore investigate the possibility of observing this spectacular signal at the LHC Run II.

Morocco

Abdesslam Arhrib

Rachid Benbrik

Identifying a light charged Higgs boson at the LHC Run II

We investigate the phenomenology of a heavy scalar ϕ of the type involved in Bekenstein's framework for varying electromagnetic coupling theories, with the difference that the scalar in our model has a large mass. The model has only two free parameters, the mass Mϕ of the scalar and the scale Λ of new physics. The scalar is dominantly produced through photon–photon fusion at the LHC and leads to a diphoton final state. It can also be produced by quark–antiquark fusion in association with a photon or a fermion pair. Its dominating decay is to diphotons, but it also has a large three-body branching to a fermion pair and a photon, which can provide an interesting search channel with a dilepton–photon resonance. We derive exclusion limits on the Mϕ−Λ plane from the latest 13 TeV LHC diphoton resonance search data. For a benchmark mass of Mϕ∼1 TeV, we find a lower limit on Λ of 18 TeV. We discuss the more complex possibility of varying couplings in the full electroweak theory and comment on the possibility that the new physics is related to extra dimensions or string theory.

Heavy photophilic scalar at the LHC from a varying electromagnetic coupling

We evaluate the prompt atmospheric neutrino flux at high energies using three different frameworks for calculating the heavy quark production cross section in QCD: NLO perturbative QCD, k T factorization including low- x resummation, and the dipole model including parton saturation. We use QCD parameters, the value for the charm quark mass and the range for the factorization and renormalization scales that provide the best description of the total charm cross section measured at fixed target experiments, at RHIC and at LHC. Using these parameters we calculate differential cross sections for charm and bottom production and compare with the latest data on forward charm meson production from LHCb at 7 TeV and at 13 TeV, finding good agreement with the data. In addition, we investigate the role of nuclear shadowing by including nuclear parton distribution functions (PDF) for the target air nucleus using two different nuclear PDF schemes. Depending on the scheme used, we find the reduction of the flux due to nuclear effects varies from 10% to 50% at the highest energies. Finally, we compare our results with the IceCube limit on the prompt neutrino flux, which is already providing valuable information about some of the QCD models.

United States

Belgium

Atri Bhattacharya

Yu Jeong

C.S. Kim

Mary Reno

Ina Sarcevic

Anna Stasto

Prompt atmospheric neutrino fluxes: perturbative QCD models and nuclear effects

We consider a class of minimal anomaly free U(1) extensions of the Standard Model with three generations of right-handed neutrinos and a complex scalar. Using electroweak precision constraints, new 13 TeV LHC data, and considering theoretical limitations such as perturbativity, we show that it is possible to constrain a wide class of models. By classifying these models with a single parameter, κ , we can put a model independent upper bound on the new U(1) gauge coupling g z . We find that the new dilepton data puts strong bounds on the parameters, especially in the mass region M Z ′ ≲ 3 TeV.

Constraining minimal anomaly free U(1) extensions of the Standard Model