Electroweak Research Articles

Discovering neutrino tridents at the Large Hadron Collider

Neutrino trident production of dilepton pairs is well recognized as a sensitive probe of both electroweak physics and physics beyond the Standard Model. Although a rare process, it could be significantly boosted by such new physics, and it also allows the electroweak theory to be tested in a new regime. We demonstrate that the forward neutrino physics program at the Large Hadron Collider offers a promising opportunity to measure for the first time, dimuon neutrino tridents with a statistical significance exceeding 5σ, improving on the previous claims at the ∼3σ level by the CHARM-II and CCFR collaborations while accounting for additional backgrounds later identified by the NuTeV collaboration. We present predictions for various proposed experiments and outline a specific experimental strategy to identify the signal and mitigate backgrounds, based on “reverse tracking” dimuon pairs in the FASERν2 detector. We also discuss prospects for constraining beyond Standard Model contributions to neutrino trident rates at high energies. Published by the American Physical Society 2024

Black Holes with Electroweak Hair

We construct static and axially symmetric magnetically charged hairy black holes in the gravity-coupled Weinberg-Salam theory. Large black holes merge with the Reissner-Nordström (RN) family, while the small ones are extremal and support a hair in the form of a ring-shaped electroweak condensate carrying superconducting W currents and up to 22% of the total magnetic charge. The extremal solutions are asymptotically RN with a mass below the total charge, M<|Q|, due to the negative Zeeman energy of the condensate interacting with the black hole magnetic field. Therefore, they cannot decay into RN black holes. As their charge increases, they show a phase transition when the horizon symmetry changes from spherical to oblate. At this point they have the mass typical for planetary size black holes of which ≈11% is stored in the hair. Being obtained within a well-tested theory, our solutions are expected to be physically relevant. Published by the American Physical Society 2024

Searching for heavy neutral leptons at a future muon collider

As the planning stages for a high energy muon collider enter a more concrete era, an important question arises as to what new physics could be uncovered. A TeV-scale muon collider is also a vector boson fusion (VBF) factory with a very clean background, and as such it is a promising environment to look for new physics that couples to the electroweak (EW) sector. In this paper, we explore the ability of a future TeV-scale muon collider to search for Majorana and Dirac heavy neutral leptons (HNLs) produced via EW bosons. Employing a model-independent, conservative approach, we present an estimation of the production and decay rate of HNLs over a mass range between 200 GeV and 9.5 TeV in two benchmark collider proposals with s=3, 10 TeV, as well as an estimation of the dominant Standard Model (SM) background. We find that exclusion limits for the mixing between the HNLs and SM neutrinos can be as low as O(10−6). Additionally, we demonstrate that a TeV-scale muon collider allows for the ability to discriminate between Majorana and Dirac type HNLs for a large range of mixing values. Published by the American Physical Society 2024

Prospects for detecting the couplings of axion-like particle with neutrinos at the CEPC

AbstractWe explore the possibility of detecting the couplings of axion-like particle (ALP) with leptons from their loop-level impact on the ALP couplings to electroweak (EW) gauge bosons via the signal process "Equation missing" at the circular electron positron collider (CEPC) and obtain prospective sensitivities to the ALP-lepton couplings. Our numerical results show that the CEPC with the center of mass energy $$\sqrt{s}=240~(91)$$ s = 240 ( 91 ) GeV and the integrated luminosity $$\mathcal {L}=5.6~(16)$$ L = 5.6 ( 16 ) $$\hbox {ab}^{-1}$$ ab - 1 might be sensitive for probing the ALP-lepton couplings in the ALP mass range from 10 GeV to 130 (50) GeV, where the prospective sensitivities to the ALP-neutrino coupling $$Tr(g_{a\nu \nu })/f_a$$ T r ( g a ν ν ) / f a can be as low as 0.016 (0.012) $$\hbox {GeV}^{-1}$$ GeV - 1 and $$0.0031~(2.8 \times 10^{-4})$$ 0.0031 ( 2.8 × 10 - 4 ) $$\hbox {GeV}^{-1}$$ GeV - 1 for $$c_{R}=0$$ c R = 0 and $$c_{R}=c_{L}$$ c R = c L , and to the ALP-charged lepton coupling $$Tr(g_{a\ell \ell })/f_a$$ T r ( g a ℓ ℓ ) / f a can be as low as 0.035 (0.07) $$\hbox {GeV}^{-1}$$ GeV - 1 for $$c_{L}=0$$ c L = 0 . We find that the prospective sensitivities given by the CEPC are not covered by the current and expected exclusion regions in some ALP mass intervals. The CEPC has the potential for exploring the ALP-neutrino couplings via some promising processes induced by the ALP-EW gauge boson couplings in the future.

Theoretical probes of Higgs boson-axion nonperturbative couplings

In this work we investigate the phenomenological implications of several nontrivial Higgs-boson- axion couplings, which cover most of the possible nonperturbative scenarios. Specifically we consider the combination of having higher-order nonrenormalizable Higgs-boson-axion couplings originating from a weakly coupled effective theory combined with nonperturbative couplings of the form ∼εΛc2|H|2cos(ϕfa). Since we consider the misalignment axion, the nonperturbative couplings can be expanded in the form of a perturbation expansion in powers of ϕ/fa, thus after the electroweak symmetry breaking, the effective potential of the axion is drastically affected by these terms. We investigate the phenomenological implications of these terms for various values of the mass scale Λc, and some scenarios are theoretically disfavored, while other scenarios with nonperturbative Higgs-boson-axion couplings of the form ∼εΛc2|H|2cos(ϕfa) with Λc∼10−10×ma and ma∼10−10 eV, lead to a characteristic pattern in the stochastic gravitational wave background via the deformation of the background equation of state parameter occurring at frequencies probed by the Einstein Telescope. We also consider loop effects from the Higgs sector caused by the term ∼εΛc2|H|2cos(ϕfa) if we close the Higgs in one loop. Published by the American Physical Society 2024

Understanding small neutrino mass and its implication

We have derived previously the relations between the neutrino masses and mixing angles in a dispersive analysis on the mixing of neutral leptonic states. The only involved assumption is that the electroweak symmetry of the Standard Model (SM) is restored at a high energy scale in some new physics scenario, which diminishes the box diagrams responsible for the mixing. Here we include corrections to the analysis up to three loops, arising from exchanges of additional neutral and charged scalars in the electroweak symmetric phase. The solution to the dispersion relation for the μ−e+-μ+e− mixing generates a typical neutrino mass mν∼O(1)eV in the SM unambiguously. The solution also favors the normal ordering of the neutrino masses over the inverted one, and links the large electroweak symmetry restoration, i.e., new physics scale to the small neutrino mass.

Bell inequality is violated in charmonium decays

The experimental data on the helicity amplitudes of charmonium decays allow us to measure entanglement in final state spin correlations and test possible violations of the Bell inequality. We find that the Bell inequality is violated with a significance of 5σ or more in the decays ηc,χc0,J/ψ→Λ+Λ¯, J/ψ→Ξ−+Ξ¯+,Ξ0+Ξ¯0,Σ−+Σ¯+,Σ0+Σ¯0, ψ(3686)→Ξ−+Ξ¯+,Σ−+Σ¯+,Σ0+Σ¯0, χc0,χc1→ϕ+ϕ. The decays ψ(3686)→Λ+Λ¯ and Ξ0+Ξ¯0 show the same violation but with less significance. The decay ψ(3686)→Ω−+Ω¯+ displays entanglement. These results firmly establish the presence of entanglement and quantum nonseparability at high energies, in a setting with particles of different spins and interacting through electroweak and strong interactions. In addition, the relatively long lifetime of some of the strange baryons produced in the decays provides a natural probe to test whether quantum spin correlations remain after the particles have interacted with the beam pipe and the first few layers of the detector. Published by the American Physical Society 2024

Ladder top-quark condensation imprints in supercooled electroweak phase transition

The electroweak (EW) phase transition in the early Universe might be supercooled due to the presence of the classical scale invariance involving Beyond the Standard Model (BSM) sectors and the supercooling could persist down till a later epoch around which the QCD chiral phase transition is supposed to take place. Since this supercooling period keeps masslessness for all the six SM quarks, it has simply been argued that the QCD phase transition is the first order, and so is the EW one. However, not only the QCD coupling but also the top Yukawa and the Higgs quartic couplings get strong at around the QCD scale due to the renormalization group running, hence this scenario is potentially subject to a rigorous nonperturbative analysis. In this work, we employ the ladder Schwinger-Dyson (LSD) analysis based on the Cornwall-Jackiw-Tomboulis formalism at the two-loop level in such a gauge-Higgs-Yukawa system. We show that the chiral broken QCD vacuum emerges with the nonperturbative top condensate and the lightness of all six quarks is guaranteed due to the accidental U(1) axial symmetry presented in the top-Higgs sector. We employ a quark-meson model-like description in the mean field approximation to address the impact on the EW phase transition arising due to the top quark condensation at the QCD phase transition epoch. In the model, the LSD results are encoded to constrain the model parameter space. We then observe the cosmological phase transition of the first-order type and discuss the induced gravitational wave (GW) productions. We find that in addition to the conventional GW signals sourced from an expected BSM at around or over the TeV scale, the dynamical topponium-Higgs system can yield another power spectrum sensitive to the BBO, LISA, and DECIGO, etc.

Monopoles and fermions in the Standard Model

We consider all magnetic monopoles that could have settled in the Standard Model after descending from a generic microscopic theory. These monopoles have Standard Model quantum numbers, are stable, and we also require that their magnetic fluxes are consistent with the electroweak symmetry breaking. Scattering processes involving quarks, leptons and protons on these monopoles are studied using partial waves decomposition. These processes in the lowest partial wave are known to be unsuppressed by the monopole mass and are relevant for monopole catalysis of proton decay. We provide estimates for scattering cross-sections and investigate and confirm the applicability of the twisted sector approach to scattering processes on these Standard Model monopoles. We find that the SM monopole catalysis processes are universal and model-independent.

Neutrino masses in the mirror twin Higgs with spontaneous ℤ2 breaking

We introduce a mirror twin Higgs model with spontaneous ℤ2 symmetry breaking that ameliorates the constraints in twin Higgs cosmology and, at the same time, generates the Standard Model neutrino masses. The model features an SU(2) triplet with hypercharge 1 alongside its twin counterpart. Spontaneous breaking of both ℤ2 and electroweak symmetry occurs in the scalar sector. The Standard Model neutrinos acquire small masses through the type-II seesaw mechanism. In contrast, their twin counterparts acquire large masses, effectively addressing the dark radiation problem in mirror twin Higgs scenarios. We study the impact of the model on the Neff. constraints, as well as on collider phenomenology.

Inverse muon decay in a circularly polarized laser field

In this paper, we investigate the effect of a circularly polarized laser field on the inverse muon decay process [Formula: see text] in electroweak theory with the exchange of a boson vector [Formula: see text]. Our method accounts for the dressing of incident electron and scattered muon by introducing the first-order laser-matter interaction of perturbation theory and using the relativistic Dirac–Volkov formalism. We have analyzed the behavior of the total cross-section (TCS) with charged-current as a function of the center-of-mass energy and the laser field parameters, such as the number of photons exchanged, the laser field strength and frequency. We have found that the circularly polarized laser field significantly affects the inverse muon decay process by reducing the TCS. We have also shown that the photonic energy transfer envelopes are perfectly symmetric with respect to the number of photons exchanged and rapidly drop when the indices of the Bessel functions are close to their arguments.

Unlocking the hidden dimension: power of chirality in scientific exploration.

In the boundless landscape of scientific exploration, there exists a hidden, yet easily accessible, dimension that has often not only intrigued and puzzled researchers but also provided the key. This dimension is chirality, the property that describes the handedness of objects. The influence of chirality extends across diverse fields of study from the parity violation in electroweak interactions to the extremely large macroscopic systems such as galaxies. In this opinion piece, we will delve into the power of chirality in scientific exploration by examining some examples that, at different scales, demonstrate its role as a key to a better understanding of our world. Our goal is to incite researchers from all fields to seek, implement and utilize chirality in their research. Going this extra mile might be more rewarding than it seems at first glance, in particular with regard to the increasing demand for new functional materials in response to the contemporary scientific and technological challenges we are facing. This article is part of the theme issue 'Celebrating the 15th anniversary of the Royal Society Newton International Fellowship'.

Electric dipole moments in 5+3 flavor weak effective theory

A fully generic treatment of electric dipole moments (EDMs) is presented in the CP-violating and flavor-conserving weak effective field theory (WET) with five flavors of quarks and three flavors of leptons. We systematically analyze leading contributions to EDMs originating from QCD and QED renormalization group running between the electroweak scale and low energy scales of about 2 GeV. We include the full one-loop anomalous dimension and a subset of two-loop corrections, as well as threshold corrections at the bottom, charm and τ masses. This allows us to derive master formulae in the space of generic WET for the neutron and proton EDMs, for EDMs of diamagnetic atoms, and for the precession frequencies constrained in molecular EDM experiments, from which bounds on the electron EDM are extracted. In particular, our master formulae capture the contributions of WET CP-violating operators with heavy quark and lepton flavors. As an application, we study EDM constraints on the Yukawa couplings of the Higgs boson, in both the linear and non-linear realizations of electroweak symmetry breaking.

The symmetry S3 in the dark matter

Experimental evidence so far suggest that there are only three generations of quarks and leptons. Before electroweak symmetry breaking, the three families of quarks and leptons are indistiguishable, so they are invariant under transformations of the S_{3} group. Using the symmetry S_{3} we have at our disposal 3 irreducible representations, \mathbf{2}, \mathbf{1}_{s}, \mathbf{1}_{a}, where we can accommodate up to four Higgs doublets in a model that occupies all the irreducible representations of the group S_{3}. This model with four Higgs doublets (4HDM) is of great interest, thanks to the fact that we can take the fourth Higgs doublet as a stable particle without interaction with fermions so that it becomes a candidate for dark matter, while with remaining three Higgses the propierties obtained are maintained. An important condition for having a viable dark matter candidate is its stability, i. e., it does not decay into Standard Model particles. The simplest way to establish the stability of a particle is imposing a discrete symmetry Z_{2}, so that all the fields are transformed in the form \Psi\longrightarrow\Psi, while the dark matter candidates are transformed as \chi\longrightarrow-\chi, this way we make sure we do not have terms denoting decays of \chi. This method will be used in 4HDM. Another imposition required to propose the candidacy of a field of the doublet H_{a}, is that its corresponding Vaccum Expectation Value (VEV) is equal to zero, v_{a}=0.

Refined determination of the weak mixing angle at low energy

The weak mixing angle is a fundamental parameter of the electroweak theory of the standard model whose measurement in the low-energy regime is still not precisely determined. Different probes are sensitive to its value, including atomic parity violation, coherent elastic neutrino-nucleus scattering, and parity-violating electron scattering on different nuclei. In this work, we attempt for the first time to combine all these various determinations by performing a global fit that also takes into account the unavoidable dependence on the experimentally poorly known neutron distribution radius of the nuclei employed, for which a new measurement using proton-cesium elastic scattering became available. By using all present direct determinations of the neutron distribution radius of cesium, we find sin2ϑW=0.2396−0.0019+0.0020, which should supersede the previous value determined from atomic parity violation on cesium. When including electroweak only, but also indirect, determinations of the neutron distribution radius of cesium, the uncertainty reduces to 0.0017, maintaining the same central value and showing excellent agreement independently of the method used. Published by the American Physical Society 2024

Consistent excesses in the search for χ~20χ~1±:\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{\ ilde{\\chi }_{2}^0\ ilde{\\chi }_{1}^\\pm :}$$\\end{document} wino/bino vs. Higgsino dark matter

The quest for supersymmetric (SUSY) particles is among the main search channels currently pursued at the LHC. Particularly, electroweak (EW) particles with masses as low as a few hundred GeV are still viable. Recent searches for the “golden channel”, pp→χ~20χ~1±→χ~10Z(∗)χ~10W±(∗)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$pp \\rightarrow \ ilde{\\chi }_{2}^0 \ ilde{\\chi }_{1}^\\pm \\rightarrow \ ilde{\\chi }_{1}^0 Z^{(*)} \\, \ ilde{\\chi }_{1}^0 W^{\\pm (*)}$$\\end{document} show consistent excesses between ATLAS and CMS in the 2 lepton, 3-lepton and mono-jet searches, assuming and Δm:=mχ~20-mχ~10≈20GeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta m:= m_{\ ilde{\\chi }_{2}^0} - m_{\ ilde{\\chi }_{1}^0} \\approx 20 \\,\\, \ extrm{GeV}$$\\end{document}. This mass configuration arises naturally in SUSY scenarios with wino/bino Dark Matter (DM) or higgsino DM. In these scenarios the lightest supersymmetric particle (LSP), assumed to be the lightest neutralino, χ~10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ilde{\\chi }_{1}^0$$\\end{document}, as a DM candidate is in good agreement with the observed limits on the DM content of the universe, as well as with negative results from Direct Detection (DD) experiments. We analyze these two scenarios with respect to the observed excesses, taking into account all relevant experimental constraints. We show that in particular wino/bino DM with different signs of the SU(2) and U(1) soft SUSY-breaking parameters can describe well the experimental excesses, while being in agreement with all other constraints.

Embedded domain walls and electroweak baryogenesis

Embedded walls are domain wall solutions which are unstable in the vacuum but stabilized in a plasma of the early Universe. We show how embedded walls in which the electroweak symmetry is restored can lead to an efficient scenario of electroweak baryogenesis. We construct an extension of the Standard Model of particle physics in which embedded walls exist and are stabilized in an electromagnetic plasma. Published by the American Physical Society 2024

Neutrino masses from new seesaw models: low-scale variants and phenomenological implications

With just the Standard Model Higgs doublet, there are only three types of seesaw models that generate light Majorana neutrino masses at tree level after electroweak spontaneous symmetry breaking. However, if there exist additional TeV scalars acquiring vacuum expectation values, coupled with heavier fermionic multiplets, several new seesaw models become possible. These new seesaws are the primary focus of this study and correspond to the tree-level ultraviolet completions of the effective operators studied in a companion publication. We are interested in the genuine cases, in which the standard seesaw contributions are absent. In addition to the tree-level generation of neutrino masses, we also consider the one-loop contributions. Furthermore, we construct low-energy versions that exhibit a very rich phenomenology. Specifically, we scrutinise the generation of dimension-6 operators and explore their implications, including non-unitarity of the leptonic mixing matrix, non-universal Z-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z-$$\\end{document}boson interactions, and lepton flavor violation. Finally, we provide (Generalised) Scotogenic-like variants that incorporate viable dark matter candidates.

Scotogenic model from an extended electroweak symmetry

We argue that the higher weak isospin SU(3)L manifestly unifies dark matter and normal matter in its isomultiplets for which dark matter carries a conserved dark charge while normal matter does not. The resultant gauge symmetry is given by SU(3)C⊗SU(3)L⊗U(1)X⊗U(1)G, where the first factor is the color group, while the rest defines a scotoelectroweak theory in which X and G determine electric charge Q=T3−1/3T8+X and dark charge D=−2/3T8+G. This setup provides both appropriate scotogenic neutrino masses and dark matter stability as preserved by a residual dark parity PD=(−1)D. Interpretation of the dark charge is further discussed, given that SU(3)L is broken at very high energy scale. Published by the American Physical Society 2024

Observation of electroweak production of W+W− in association with jets in proton-proton collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV with the ATLAS detector

A measurement of the production of W bosons with opposite electric charges in association with two jets is presented based on 140 fb−1 of data collected by the ATLAS detector in proton-proton collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV. The analysis is sensitive to the scattering of W bosons, which is of particular interest in the ATLAS physics programme as it can be used to probe the electroweak symmetry breaking mechanism of the Standard Model. This signal is observed with a significance of 7.1 standard deviations above the background expectation, while 6.2 standard deviations were expected. The measured cross-section is determined in a signal-enriched fiducial volume and is found to be 2.7 ± 0.5 fb, which is consistent with the theoretical prediction of 2.20−0.13+0.14\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {2.20}_{-0.13}^{+0.14} $$\\end{document} fb.