Light Scalar Boson Research Articles

Gravitational wave probe of primordial black hole origin via superradiance

In this article we have used stochastic gravitational wave background as a unique probe to gain insight regarding the creation mechanism of primordial black holes. We have considered the cumulative gravitational wave background which consists of the primary part coming from the creation mechanism of the primordial black holes and the secondary part coming from the different mechanisms the primordial black holes go through. We have shown that in the presence of light or ultra light scalar bosons, superradiant instability generates the secondary part of the gravitational wave background which is the most detectable. In order to show the unique features of the cumulative background, we have consdiered the delayed vacuum decay during a first order phase transition as the origin of primordial black holes. We have shown the dependence of the features of the cumulative background, such as the mass of the relevant light scalars, peak frequencies, etc. on the transition parameters. We have also generated the cumulative background for a few benchmark cases to further illustrate our claim.

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

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.

Sensitivity potential to a light flavor-changing scalar boson with DUNE and NA64mu

In this work, we report on the sensitivity potential of complementary muon-on-target experiments to new physics using a scalar boson benchmark model associated with charged lepton flavor violation. The NA64mu experiment at CERN uses a 160-GeV energy muon beam with an active target to search for excess events with missing energy and momentum as a probe of new physics. At the same time, the proton beam at Fermilab, which is used to produce the neutrino beam for the Deep Underground Neutrino Experiment (DUNE), will also produce a high-intensity muon beam dumped in an absorber. Combined with the liquid argon near detector, the system could be used to search for similar scalar boson particles with a lower-energy but higher-intensity beam. We find that both NA64mu and DUNE could cover new, unexplored parts of the parameter space of the same benchmark model, providing a complementary way to search for new physics.

Stellar cooling limits on light scalar boson revisited

We revisit the stellar cooling limits on the light scalar boson whose coupling to the Standard Model particles is described by its mixing with the Higgs boson. Strong constraints have been obtained from the electron-nucleus bremsstrahlung process (Ne→NeS) and the resonant plasma effect in the medium. We find that the bremsstrahlung contribution from the electron and nucleus scattering is of similar magnitude to the plasma mixing effect including the off-resonant mixing. The constraints on the scalar coupling are found to be about three orders of magnitude weaker than the previous evaluations because of the missing factor of the electron-nucleon mass ratio. For white dwarfs, the stellar cooling constraint is even more suppressed due to the Pauli blocking effect. We obtain limits on the Higgs-scalar mixing angle of 10−10–10−9, which are given by white dwarfs or red giants up to the luminosity limits, in the region where the scalar mass is lighter than about 10 keV.

Scrutinizing the 95–100 GeV di-tau excess in the top associated process

Recently, the CMS collaboration has reported a di-tau excess with a local significance of 2.6–3.1sigma where the invariant mass is m_{tau tau } =95–100 GeV. This excess can be interpreted as a light scalar boson that couples to the third generation fermions, particularly top and tau . Based on the simplest model that can account for the CMS di-tau excess, we evaluate experimental sensitivities to the additional light resonance, using the results reported by the ATLAS collaboration. We see that a search for the top-quark associated production of the SM Higgs boson that decays into tau {bar{tau }} sets a strong model-independent limit. We also find that the CP-even scalar interpretation of the light resonance is excluded by the ATLAS results, while the CP-odd interpretation is not.

Neutrino bound states and bound systems

Yukawa interactions of neutrinos with a new light scalar boson ϕ can lead to formation of stable bound states and bound systems of many neutrinos (ν-clusters). For allowed values of the coupling y and the scalar mass mϕ, the bound state of two neutrinos would have the size larger than 1012 cm. Bound states with sub-cm sizes are possible for keV scale sterile neutrinos with coupling y > 10−4. For ν-clusters we study in detail the properties of final stable configurations. If there is an efficient cooling mechanism, these configurations are in the state of degenerate Fermi gas. We formulate and solve equations of the density distributions in ν-clusters. In the non-relativistic case, they are reduced to the Lane-Emden equation. We find that (i) stable configurations exist for any number of neutrinos, N; (ii) there is a maximal central density ∼ 109 cm−3 determined by the neutrino mass; (iii) for a given mϕ there is a minimal value of Ny3 for which stable configurations can be formed; (iv) for a given strength of interaction, Sϕ = (ymν/mϕ)2, the minimal radius of ν-clusters exists. We discuss the formation of ν-clusters from relic neutrino background in the process of expansion and cooling of the Universe. One possibility realized for Sϕ > 700 is the development of instabilities in the ν-background at T < mν which leads to its fragmentation. For Sϕ ∈ [70, 700]) they might be formed via the growth of initial density perturbations in the ν-background and virialiazation, in analogy with the formation of Dark Matter halos. For allowed values of y, cooling of ν-clusters due to ϕ-bremsstrahlung and neutrino annihilation is negligible. The sizes of ν-clusters may range from ∼ km to ∼ 5 Mpc.

Probing light mediators and (g − 2)μ through detection of coherent elastic neutrino nucleus scattering at COHERENT

We present the constraints on the parameters of several light boson mediator models obtained from the analysis of the current data of the COHERENT CEνNS experiment. We consider a variety of vector boson mediator models: the so-called universal, the B − L and other anomaly-free U(1)′ gauge models with direct couplings of the new vector boson with neutrinos and quarks, and the anomaly-free Le− Lμ, Le− Lτ, and Lμ− Lτ gauge models where the coupling of the new vector boson with the quarks is generated by kinetic mixing with the photon at the one-loop level. We consider also a model with a new light scalar boson mediator that is assumed, for simplicity, to have universal coupling with quarks and leptons. Since the COHERENT CEνNS data are well-fitted with the cross section predicted by the Standard Model, the analysis of the data yields constraints for the mass and coupling of the new boson mediator that depend on the charges of quarks and neutrinos in each model under consideration. We compare these constraints with the limits obtained in other experiments and with the values that can explain the muon g − 2 anomaly in the models where the muon couples to the new boson mediator.

Constraining ultralight axions with galaxy surveys

Ultralight axions and other bosons are dark matter candidates present in many high energy physics theories beyond the Standard Model. In particular, the string axiverse postulates the existence of up to \U0001d4aa(100) light scalar bosons constituting the dark sector. We test the validity of the effective field theory of large-scale structure approach to mixed ultralight axion dark matter by making our own mock galaxy catalogs and find an anisotropic ultralight axion signature in the galaxy quadrupole. We use the Fourier-space galaxy clustering statistics from the Baryon Oscillation Spectroscopic Survey (BOSS) and obtain upper bounds for the axion relic density Ω_a h2<0.004 for axions of mass 10-31 eV≤ m_a≤ 10-26 eV at 95% confidence. We also improve existing constraints by a factor of over 4.5 and 2.1 for axion masses of 10-25 eV and 10-32 eV compared to CMB alone. To improve the convergence speed of our analysis, we develop an augmented interpolation scheme allowing a fast computation of the axion contribution to the linear matter power spectrum. This method leads to a 70% reduction of the computational cost for the full Monte Carlo Markov chains analysis.

Light dark bosons in the JUNO-TAO neutrino detector

This work presents a sensitivity study of a reactor liquid scintillator detector to three kinds of dark bosons with masses below 1 MeV, such as dark photons, axion-like particles and light scalar bosons. The JUNO-TAO detector with Taishan nuclear reactor is taken as a reference. With proposed 180 days data taking, the sensitivity to the dark bosons can reach $\sim10^{-5}$ 95%C.L. for the optimized signal to background ratio for the electron coupling constant $\it{g_X} $ through inverse Compton-like scattering. Similar calculations are completed for axion-like particles and scalar bosons. The background systematic uncertainty presents as the main limiting factor for the further sensitivity improvement. Several remarks are made to the controversial analysis for the NEOS experiment. Additionally the differential and the inverse differential cross sections have been derived for all three boson types and their interactions with electrons in liquid scintillator.

New physics searches at the ILC positron and electron beam dumps

We study capability of the ILC beam dump experiment to search for new physics, comparing the performance of the electron and positron beam dumps. The dark photon, axion-like particles, and light scalar bosons are considered as new physics scenarios, where all the important production mechanisms are included: electron-positron pair-annihilation, Primakoff process, and bremsstrahlung productions.We find that the ILC beam dump experiment has higher sensitivity than past beam dump experiments, with the positron beam dump having slightly better performance for new physics particles which are produced by the electron-positron pair-annihilation.

Explaining Atomki anomaly and muon g \u2212 2 in U(1)X extended flavour violating two Higgs doublet model

We investigate a two Higgs doublet model with extra flavour depending U(1)X gauge symmetry where Z′ boson interactions can explain the Atomki anomaly by choosing appropriate charge assignment for the SM fermions. For parameter region explaining the Atomki anomaly we obtain light scalar boson with mathcal{O} (10) GeV mass, and we explore scalar sector to search for allowed parameter space. We then discuss anomalous magnetic dipole moment of muon and lepton flavour violating processes induced by Yukawa couplings of our model.

Dark photon from light scalar boson decays at FASER

FASER is one of the promising experiments which search for long-lived particles beyond the Standard Model. In this paper, we focus on dark photon associating with an additional U(1) gauge symmetry, and also a scalar boson breaking this U(1) gauge symmetry. We study the sensitivity to the dark photon originated from U(1)-breaking scalar decays. We find that a sizable number of dark photon signatures can be expected in wider parameter space than previous studies.

Gravitational waves from the fragmentation of axion-like particle dark matter

The misalignment mechanism allows for the efficient, and usually very cold, production of light scalar bosons, such as axion-like particles (ALPs), making them an appealing dark matter candidate. However, in certain cases, such as in the presence of a monodromy, the self-interactions of ALPs can be sufficiently strong such that the homogeneous field fragments soon after the onset of oscillations. The resulting large inhomogeneities can lead to the production of gravitational waves (GWs). We investigate the nonlinear dynamics of fragmentation, as well as of the subsequent turbulent regime, and calculate the stochastic GW background that is produced from this process. The GW background can be enhanced if the time evolution features an extended intermediate phase of ultrarelativistic dynamics due to a small mass at the bottom of the potential. Yet, this enhancement is limited by the requirement that the dark matter remains sufficiently cold. In some cases the resulting GWs may be within reach of future GW detectors, allowing a complementary probe of this type of dark matter.

Sommerfeld enhancements for asymmetric dark matter

We extend the analysis of asymmetric Dark Matter relic density with the Sommerfeld enhancement to the case where the mediator is massive. In asymmetric Dark Matter models, asymmetric Dark Matter is assumed to couple to the light scalar or vector boson. Asymmetric Dark Matter annihilation cross section is enhanced by the Sommerfeld effect which exists due to the distortion of the wavefunction of asymmetric Dark Matter particle and anti–particle by long–range interactions. The impacts of the Sommerfeld enhancement on the relic densities of asymmetric Dark Matter particle and anti–particle are discussed. The effect of kinetic decoupling on the relic density is also probed when the annihilation cross section is boosted by the Sommerfeld enhancement. Finally, the constraints on the parameter space are given using the observational data of the relic density of Dark Matter.

New physics at the MUonE experiment at CERN

A confirmation of the long-standing muon $g$-2 discrepancy requires both experimental and theoretical progress. On the theory side, the hadronic corrections are under close scrutiny, as they induce the leading uncertainty of the Standard Model prediction. Recently, the MUonE experiment has been proposed at CERN to provide a new determination of the leading hadronic contribution to the muon $g$-2 via the measurement of the differential cross section of muon-electron scattering. The precision expected at this experiment raises the question whether possible new-physics (NP) could affect its measurements. We address this issue studying possible NP signals in muon-electron collisions due to heavy or light mediators, depending on whether their mass is higher or lower than ${\cal O} (1{\rm GeV})$. We analyze the former in a model-independent way via an effective field theory approach, whereas for the latter we focus on scenarios with light scalar and vector bosons. Using existing experimental bounds, we show that possible NP effects in muon-electron collisions are expected to lie below MUonE's sensitivity. This result confirms and reinforces the physics case of the MUonE proposal.

Fermion mass splitting in the technicolor coupled scenario

We discuss fermion mass generation in unified models where QCD and technicolor (or any two strongly interacting theories) have their Schwinger–Dyson equations coupled. In this case the technicolor (TC) and QCD self-energies are modified in comparison with the behavior observed in the isolated theories. In these models the pseudo-Goldstone boson masses are much higher than the ones obtained in different contexts, and phenomenological signals, except from a light scalar composite boson, will be quite difficult to be observed at present collider energies. The most noticeable fact of these models is how the mass splitting between the different ordinary fermions is generated. We discuss how a necessary horizontal (or family) symmetry can be implemented in order to generate the mass splitting between fermions of different generations; how the fermionic mass spectrum may be modified due to GUT interactions, as well as how the mass splitting within the same fermionic generation are generated due to electroweak and GUT interactions.

Search for physics beyond the standard model in multilepton final states in proton-proton collisions at sqrt{s} = 13 TeV

A search for physics beyond the standard model in events with at least three charged leptons (electrons or muons) is presented. The data sample corresponds to an integrated luminosity of 137 fb−1 of proton-proton collisions at sqrt{s} = 13 TeV, collected with the CMS detector at the LHC in 2016–2018. The two targeted signal processes are pair production of type-III seesaw heavy fermions and production of a light scalar or pseudoscalar boson in association with a pair of top quarks. The heavy fermions may be manifested as an excess of events with large values of leptonic transverse momenta or missing transverse momentum. The light scalars or pseudoscalars may create a localized excess in the dilepton mass spectra. The results exclude heavy fermions of the type-III seesaw model for masses below 880 GeV at 95% confidence level in the scenario of equal branching fractions to each lepton flavor. This is the most restrictive limit on the flavor-democratic scenario of the type-III seesaw model to date. Assuming a Yukawa coupling of unit strength to top quarks, branching fractions of new scalar (pseudoscalar) bosons to dielectrons or dimuons above 0.004 (0.03) and 0.04 (0.03) are excluded at 95% confidence level for masses in the range 15–75 and 108–340 GeV, respectively. These are the first limits in these channels on an extension of the standard model with scalar or pseudoscalar particles.

Probing long-lived particles at Higgs factories

We study displaced vertex signatures of long-lived particles (LLPs) from exotic Higgs decays in the context of a Higgs-portal model and a neutral-naturalness model at the circular electron positron collider (CEPC) and future circular collider ${e}^{+}\text{ }{e}^{\ensuremath{-}}$ (FCC-ee). Such two models feature two representative mass ranges for LLPs, which show very different behavior in their decay signatures. The Higgs-portal model contains a very light sub-GeV scalar boson stemming from a singlet scalar field appended to the Standard Model. Such a light scalar LLP decays into a pair of muons or pions, giving rise to a distinctive signature of collimated muon-jet or pion-jet, thanks to the sub-GeV mass. On the other hand, the neutral-naturalness model, e.g., folded supersymmetry, predicts the lightest mirror glueball of mass $O(10)\text{ }\text{ }\mathrm{GeV}$, giving rise to long decays with a large transverse impact parameter because of the relatively large mass. Utilizing such distinct characteristics to remove the background, we estimate the sensitivities of searches for light scalar bosons and mirror glueballs at the CEPC and FCC-ee. We find either complementary or stronger coverage compared to the previous results in the similar contexts.

Eta decay and muonic puzzles

New physics motivated by muonic puzzles (proton radius and muon g−2 discrepancies) is studied. Using a light scalar boson ϕ, assuming Yukawa interactions, accounts for these muonic puzzles simultaneously. Our previous work limits the existence of such a scalar boson's mass mϕ from about 160 keV to 60 MeV. We improve this result by including the influence of all of the possible particles that couple to the ϕ in computing the decay rate. Doing this involves including the strong interaction physics, involving quarks, necessary to compute the ηπϕ vertex function. The Nambu-Jona-Lasinio model, which accounts for the spontaneous symmetry breaking that yields the constituent mass is employed to represent the relevant strong-interaction physics. We use the ηπϕ vertex function to reanalyze the electron beam dump experiments. The result is that the allowed range of mϕ lies between about 160 keV and 3.5 MeV. This narrow range represents an inviting target for ruling out or discovering this scalar boson. A possible UV completion of our phenomenological model is discussed.