Light Boson Research Articles

Dark matter as the trigger of flavor changing neutral current decays of the top quark

We suggest a simplified model that simultaneously addresses the dark matter problem and gives rise to top-quark flavor changing neutral current (FCNC) interactions at the one-loop order. The model consists of two extra SU(2)L gauge singlets: a colored mediator of spin zero (S) and a right-handed fermion (χ); both are odd under an Z2 symmetry. The right-handed fermion plays the role of the dark matter candidate. In this model, the presence of the two dark sector particles generates one-loop induced FCNC decays of the top quark into light quarks and bosons such as the gluon, the photon, the Z boson, or the Higgs boson. As a case study, we analyze the top-quark FCNC decays into light quarks (u or c) and Z or Higgs bosons. We then study the reliable solutions to the dark matter problem by estimating the regions in the parameter space that are consistent with the measurement of the dark matter relic density. We also revisit the bounds from the searches of dark matter in events with at least one high-pT jet and large missing transverse energy at the Large Hadron Collider (LHC). We then define four benchmark points that are consistent with the existing constraints from collider experiments and cosmology. We finally estimate, for these benchmark scenarios, the rates of a broad range of channels that can be used to probe the connection between the top FCNC transitions and dark matter, both at the HL-LHC and at a future 100 TeV collider. Published by the American Physical Society 2024

Two pseudo-Goldstone bosons in the Gildener–Weinberg model

In a dimensionless multi-scalar extension of the Standard Model, Gildener and Weinberg assumed that along a flat direction, there is only one classically massless scalar, known as the scalon, which acquires mass through radiative corrections à la Coleman–Weinberg, while all other scalars remain heavy. In this paper, by introducing a toy model with four scalar degrees of freedom we demonstrate the existence of two scalons along a specific flat direction that we construct. We present the effective potential for the model and provide the masses of the heavy scalars and two radiatively light pseudo-Goldstone bosons.

Future targets for light gauge bosons from cosmic strings

Cosmic strings, theoretical one-dimensional topological defects from the early universe, provide a valuable opportunity for exploring dark matter (DM) production and gravitational wave (GW) emission. Our study investigates the production of gauge bosons and GW emission from cosmic string decay, considering the constraints imposed by cosmological observations. We specifically examine how gauge bosons radiated from strings contribute to DM and dark radiation, with limits set by the observed DM abundance and cosmic microwave background data, respectively. Additionally, we analyze the gravitational wave spectrum of this model across both low and high frequencies. Notably, the spectrum typically follows a f−1/3 pattern at high frequencies, beyond the pivot frequency f∗. We derive an analytical expression for the frequency f∗ and confirm its accuracy through numerical verification. Furthermore, we compare the GW spectrum of this model with the forecasted capabilities of future GW observatories, such as the Einstein Telescope, the Laser Interferometer Space Antenna, the Big Bang Observer, and μAres. Finally, we discuss how these considerations impact the model parameters, specifically the gauge boson mass and the energy scale of U(1) symmetry breaking, providing insights into how cosmic strings could enhance our understanding of DM and GW astronomy.

Search for the production of dark matter in the framework of a mono- Z′ portal at the ILC with simulated electron-positron collisions at s=500 GeV

In the present work, we study the possible production of the light neutral gauge boson (Z′) candidates, which originated from a simplified-model scenario based on the mono-Z′ model, in association with dark matter. This study has been performed by studying events with dimuon plus missing transverse energy produced in the simulated electron-positron collisions at the foreseen International Linear Collider (ILC), operating at 500 GeV center of mass energy and integrated luminosity of 1000 fb−1. In case no new physics has been discovered, we set upper limits at 95% confidence level on the masses of various particles in the model as, spin-1 (Z′), as well as the fermionic dark matter. Published by the American Physical Society 2024

Impact of the cosmic neutrino background on long-range force searches

Light bosons can mediate long-range forces. We show that light bosonic mediators interacting with a background medium, in particular, with the cosmic neutrino background (CνB), may induce medium-dependent masses which could effectively screen long-range forces from detection. This leads to profound implications for long-range force searches in e.g. the Eöt-Wash, MICROSCOPE, and lunar laser-ranging (LLR) experiments. For instance, we find that when the coupling of the mediator to neutrinos is above 3 × 10−10 or 5 × 10−13, bounds from LLR and experiments employing the Sun as an attractor, respectively, would be entirely eliminated. Larger values of the coupling can also substantially alleviate bounds from searches conducted at shorter distances.

Searching for a new light gauge boson with axial couplings in muon beam dump experiments

We present a formalism for new U(1) interactions involving weak hypercharge, baryon, and lepton numbers, and a possible axial symmetry generator FA in the presence of a second Brout-Englert-Higgs doublet. The resulting U boson, after mixing with the Z, interpolates between a generalised dark photon, a dark Z, and an axially coupled gauge boson. We especially focus on the axial couplings originating from FA or from mixing with the Z, determined by the scalar sector via parameters like tan β and the v.e.v. of an extra dark singlet.We explore the distinctive features of axially coupled interactions, especially in the ultrarelativistic limit, where the U boson behaves much as an axion-like particle, with enhanced interactions to quarks and leptons. This enhancement is particularly relevant for future muon beam dump experiments, since the muon mass considerably increases the effective coupling, proportional to 2mμ/mU, compared to analogous experiments with electrons.We also analyse the shape of the expected beam dump exclusion or discovery regions, influenced by U boson interactions and the experiment geometry. Different situations are considered, limited in particular by cases for which the U decays before reaching the detector, or has too small couplings to produce detectable events. We also compare to vectorially coupled bosons and axion-like pseudoscalars, highlighting the importance of understanding the parameter space for future experiment design and optimisation.

Theoretical motivations for hidden light bosons

Theoretical motivations for hidden light bosons

Can quantum Rabi model with A2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\varvec{A}}^\ extbf{2}$$\\end{document}-term avoid no-go theorem and make quantum simulation of mass-enhancement in SUSY breaking?

We study the model of a mass enhancement in the supersymmetric quantum mechanics. This model is so simple that it may be implemented as a quantum simulation of the mass enhancement taking place when supersymmetry (SUSY) is spontaneously broken. It is evolved from a prototype based on the quantum Rabi model. Here, our quantum simulation means the realization of the target quantum phenomenon as a physical entity with some quantum-information devices. The original prototype is given as a mathematical model, and has the transition from the N=2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathcal {N}}=2$$\\end{document} SUSY to its spontaneous breaking, though it has no mass enhancement. It is recently reported that the transition is observed for this prototype in a trapped-ion experiment with devising a method experimentally to realize the transition. The model proposed in this paper describes how the mass enhancement takes place in the fermionic states by the excitation of the 1-mode light boson in the SUSY breaking. In this model, the bosonic and fermionic states are graded by qubits. Although our model’s interaction does not have the Higgs potential, the mass enhancement in the fermionic states is caused by the radiative enhancement with the help of the X-gate’s swap between the fermionic and bosonic states.

Search for the decay of the Higgs boson to a pair of light pseudoscalar bosons in the final state with four bottom quarks 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}$$ \\sqrt{\ extrm{s}} $$\\end{document} = 13 TeV

A search is presented for the decay of the 125 GeV Higgs boson (H) to a pair of new light pseudoscalar bosons (a), followed by the prompt decay of each a boson to a bottom quark-antiquark pair, H→aa→bb¯bb¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ extrm{H}\ o \ extrm{aa}\ o \ extrm{b}\\overline{\ extrm{b}}\ extrm{b}\\overline{\ extrm{b}} $$\\end{document}. The analysis is performed using a data sample of proton-proton collisions collected with the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb−1. To reduce the background from standard model processes, the search requires the Higgs boson to be produced in association with a leptonically decaying W or Z boson. The analysis probes the production of new light bosons in a 15 < ma < 60 GeV mass range. Assuming the standard model predictions for the Higgs boson production cross sections for pp → WH and ZH, model independent upper limits at 95% confidence level are derived for the branching fraction BH→aa→bb¯bb¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{B}\\left(\ extrm{H}\ o \ extrm{aa}\ o \ extrm{b}\\overline{\ extrm{b}}\ extrm{b}\\overline{\ extrm{b}}\\right) $$\\end{document}. The combined WH and ZH observed upper limit on the branching fraction ranges from 1.10 for ma = 20 GeV to 0.36 for ma = 60 GeV, complementing other measurements in the μμττ, ττττ and bbℓℓ (ℓ = μ, τ) channels.

Naturalness-motivated composite Higgs model for generating the top Yukawa coupling

The large top Yukawa coupling results in the top quark contributing significantly to the quantum correction of the Higgs mass term. Traditionally, this effect is canceled by the presence of top partners in symmetry-based models. However, the absence of light top partners poses a challenge to the naturalness of these models. In this paper, we study a model based on composite Higgs with the top Yukawa coupling originating from dimension-six four-fermion operators. The low cutoff scale of the top quark loop required by the naturalness principle can be realized with a light gauge boson Eμ that connects the hyperfermions and top quarks. A scalarless dynamical model with weakly coupled extended SU(4)EC gauge group is presented. The model features an Eμ boson and a ZE′ boson both at the sub-TeV scale, which lead to a rich phenomenology, especially in the top quark physics. Published by the American Physical Society 2024

Low-mass dark sector searches with deuteron photodisintegration

Recent years have seen much activity in searches for dark-sector messenger particles in the 10–100 MeV mass range, especially in view of a potential new light boson conjectured by the ATOMKI Collaboration, X17. Under the assumption that the messenger particle has definite parity and either zero or unit spin, quite stringent bounds already exist on its coupling to electrons and protons. Equally stringent bounds on the neutron coupling do not exist yet, but are nonetheless desirable. We explore how measurements of deuteron photodisintegration with a quasifree neutron can yield bounds on the neutron coupling, and compute projections for a potential measurement at the low-energy high-intensity electron scattering experiment MAGIX@MESA. The projected bounds are found to be competitive for an axial-vector or pseudoscalar scenario, but not for a vector or scalar scenario. Published by the American Physical Society 2024

Light new physics in B→K(*)νν¯ ?

The study of the rare decays B→K(*)νν¯ offers a window into the dynamics operating at the electroweak scale, allowing studies of the Standard Model and searches for heavy new physics. However, the analysis of these decays is also potentially sensitive to the on shell production of new light bosons X through the process B→K(*)X. In particular, Belle II has recently measured B+→K+νν¯, finding a 2.8σ excess under the assumption of heavy new physics. Since this excess is rather localized in the kaon energy, a fit that includes the decay mode B+→K+X to the kinematic distributions prefers mX≈2 GeV with branching fraction Br[B→KX]=(8.8±2.5)×10−6 and a significance of ≈3.6σ. However, no excess was found in the measurements of B→K(*)νν¯, and a global analysis of the Belle II and data leads to Br[B→KX]=(5.1±2.1)×10−6 with a reduced significance of ≈2.4σ. We then study various simplified dark-flavored models and present a possible UV completion based on a gauged B3−L3 symmetry, highlighting the discovery potential of dedicated searches for B→K(*)X at Belle II. Published by the American Physical Society 2024

GRB221009A gamma-ray events from nonstandard neutrino self-interactions

The flux of high-energy astrophysical neutrinos observed by the present generation of neutrino detectors has already indicated a few hints of new physics beyond the Standard Model. In this work, we show that high-energy gamma-ray observations can also be considered as a complementary probe for unveiling the source of high-energy astrophysical neutrino events and new physics. Recently, the LHAASO collaboration has reported O(5000) gamma-ray events in the energy range between 0.5–18 TeV from gamma-ray burst GRB 221009A within 2000 seconds after the initial outburst. We showed that some of the high-energy gamma rays can be produced from the interaction of astrophysical neutrinos with CMB neutrinos through nonstandard self-interaction of neutrinos mediated by light scalar bosons. The nonstandard interaction of neutrinos recently took a lot of attention in cosmology for its role in reducing Hubble tension. We have constrained the parameter space of nonstandard self-interacting neutrinos from the flux of photons observed by LHAASO and showed consistency of the same with the resulting parameter space from Hubble tension requirements and other recent constraints from laboratory/cosmology. Published by the American Physical Society 2024

Flavour-changing top quark decays in the alternative left-right model

We examine flavour-changing neutral-current decays of the top quark, t→qγ, t→qZ, t→qH, and t→qg (with q=u,c), in the Alternative Left-Right Model, a left right-symmetric model featuring exotic quarks and light bosons. These decays have a very small probability of occurring within the Standard Model, but they can be enhanced in this model through the presence of the exotic states. While associated signals may be detected directly at the LHC, rare decays have the advantage of offering means to probe new particles indirectly, through loop-contributions. We perform a comprehensive analysis of the model's parameter space to demonstrate the possible existence of enhancements in the corresponding branching ratios, of 106 for the branching ratios B(t→uZ) and B(t→uH), and in the range of 102−104 for the other decays, relative to the Standard Model. We subsequently determine the preferred parameter space regions of the model in terms of potential of being reached in the near future.

Searching for the light leptophilic gauge boson Z x via four-lepton final states at the CEPC* *Supported by the National Natural Science Foundation of China (11875157, 12147214)

We investigate the possibility of detecting the leptophilic gauge boson predicted by the model via the processes and at the Circular Electron Positron Collider (CEPC) with a center of mass energy GeV and luminosity . We provide the expected sensitivities of the CEPC to the parameter space at the , , , and levels.

Resolving the muon g − 2 tension through Z′-induced modifications to σhad

The QED hadronic vacuum polarization function plays an important role in the determination of precision electroweak observables and of the anomalous magnetic moment of the muon. These contributions have been computed from data, by means of dispersion relations affecting the electron positron hadronic cross sections, or by first principle lattice-QCD computations in the Standard Model. Today there is a discrepancy between the two approaches for determining these contributions, which affects the comparison of the measurement of the anomalous magnetic moment of the muon with the theoretical predictions. In this article, we revisit the idea that this discrepancy may be explained by the presence of a new light gauge boson that couples to the first generation quark and leptons and has a mass below the GeV scale. We discuss the requirements for its consistency with observations and the phenomenological implications of such a gauge extension.

Flavour constraints on light spin-1 bosons within a chiral Lagrangian approach

We discuss the construction of the chiral Lagrangian for a light spin-1 boson, here denoted as X, featuring both vector and axial-vector couplings to light u, d, s quarks. Focusing on ∆S = 1 transitions, we show that there are model-independent tree-level contributions to K±→ π±X, sourced by Standard Model charged currents, which receive an mK2/mX2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {m}_K^2/{m}_X^2 $$\\end{document} enhancement from the emission of a longitudinally polarized X. This flavour observable sets the strongest to date model-independent bound on the diagonal axial-vector couplings of X to u, d, s quarks for mX< mK– mπ, superseding the bounds arising from beam-dump and collider searches.

A generic formation mechanism of ultralight dark matter solar halos

As-yet undiscovered light bosons may constitute all or part of the dark matter (DM) of our Universe, and are expected to have (weak) self-interactions. We show that the quartic self-interactions generically induce the capture of dark matter from the surrounding halo by external gravitational potentials such as those of stars, including the Sun. This leads to the subsequent formation of dark matter bound states supported by such external potentials, resembling gravitational atoms (e.g. a solar halo around our own Sun). Their growth is governed by the ratio ξ foc ≡ λdB/R ⋆ between the de Broglie wavelength of the incoming DM waves, λdB, and the radius of the ground state R ⋆.For ξ foc ≲ 1, the gravitational atom grows to an (underdense) steady state that balances the capture of particles and the inverse (stripping) process. For ξ foc ≳ 1, a significant gravitational-focusing effect leads to exponential accumulation of mass from the galactic DM halo into the gravitational atom. For instance, a dark matter axion with mass of the order of 10-14 eV and decay constant between 107 and 108 GeV would form a dense halo around the Sun on a timescale comparable to the lifetime of the Solar System, leading to a local DM density at the position of the Earth 𝒪(104) times larger than that expected in the standard halo model. For attractive self-interactions, after its formation, the gravitational atom is destabilized at a large density, which leads to its collapse; this is likely to be accompanied by emission of relativistic bosons (a `Bosenova').

A unified cosmological dark sector from a Bose–Einstein condensate

We examine the viability of cosmological solution(s) describing a unified picture of the dark side of the universe from a Bose–Einstein condensate (BEC) of light bosons. The energy density of the BEC, together with its quantum potential, can indeed account for such a unification, in the sense that the (dust-like) cold dark matter and the dark energy components emerge from the same source. In particular, the bulk of the dark energy can be attributed to the quantum potential, in the quantum corrected Raychaudhuri–Friedmann equation, when the ‘macroscopic’ BEC wave-function is taken to be such that the corresponding probability density is construed as the energy density of the dusty fluid. However, there arises a purely quantum mechanical back-reaction, of even the visible baryons, on the effective dark energy and dark matter contents, which crucially determines the mass of the BEC. We determine the constraint on such a back-reaction, and hence on the BEC mass, from physical considerations, as well as estimate the same using recent observational data.

Composite scalar bosons masses: Effective potential versus Bethe-Salpeter approach

Ten years ago the 125 GeV Higgs resonance was discovered at the LHC [1,2], if this boson is a fundamental particle or a particle composed of new strongly interacting particles is still an open question. If this is a composite boson there are still no signals of other possible composite states of this scheme, a possible solution to this problem was recently discussed in Refs. [30,31], where it is argued that the Higgs boson can be a composite dilaton [30]. In this work, considering an effective potential for composite operators we verify that the potential responsible for a light composite scalar boson of O(120) GeV, behaves like ∝Φ4 suggesting that if the Higgs boson is a composite scalar it may be a composite dilaton.