Lightest Stable Particle Research Articles

Radiative corrections to aid the direct detection of the Higgsino-like neutralino dark matter: Spin-independent interactions

The lightest neutralino (χ˜10) is a good dark matter (DM) candidate in the R-parity conserving minimal supersymmetric Standard Model. In this work, we consider the light Higgsino-like neutralino as the lightest stable particle, thanks to a rather small Higgsino mass parameter μ. We then estimate the prominent radiative corrections to the neutralino-neutralino-Higgs boson vertices. We show that for Higgsino-like χ˜10, these corrections can significantly influence the spin-independent direct detection cross section, even contributing close to 100% in certain regions of the parameter space. These corrections, therefore, play an important role in deducing constraints on the mass of the Higgsino-like lightest neutralino DM, and thus the μ parameter. Published by the American Physical Society 2024

Fermionic dark matter in Dynamical Scotogenic Model

In the Dynamical Scotogenic Model, the global B − L symmetry is supposed to be broken spontaneously resulting in a massless Goldstone boson called majoron, and massive right handed neutrinos which participate in the generation of light neutrino massses at one-loop. One of them being the lightest stable particle can be a thermal dark matter candidate. We discuss how the dark matter phenomenology differs from the original Scotogenic model, taking into account all the constraints coming from the observed neutrino masses and mixing, lepton flavor violations such as μ → eγ, μ → eJ, astrophysical and cosmological observations of stellar cooling and Neff, as well as collider signatures such as Higgs invisible decays. We find that the dark matter annihilation to majorons plays an important role to produce the right relic abundance.

Connecting ANITA anomalous events to a nonthermal dark matter scenario

The ANtarctic Impulsive Transient Antenna (ANITA) collaboration has observed two EeV-energy, upward going events originating from below the horizon. As no standard model (SM) particles, propagating through the earth at such energy and exit angles, can give rise to the required survival probability for the observed events, several beyond standard model (BSM) proposals have come up. We propose a scenario where a $Z_2$ odd sector is responsible for such anomalous events. The next to lightest $Z_2$ odd particle or the next to lightest stable particle (NLSP), created from ultra high energy neutrino interactions with nucleons, can pass through the earth and then decay into the lightest $Z_2$ odd particle or the lightest stable particle (LSP) and a tau lepton. The long-lived nature of the NLSP requires its coupling with the LSP to be very small, keeping the LSP out of thermal equilibrium in the early universe. The LSP can then be a non-thermal dark matter while the tau leptons produced from NLSP decay after passing through the earth can explain the ANITA events. We first show that a purely non-thermal dark matter scenario can not give rise to the required event rates while a hybrid scenario where dark matter can have both thermal as a well non-thermal contribution to its relic abundance, serves the purpose.

Restrictions on the parameters of the Minimal Supersymmetric Standard Model with CP-violation

The minimal supersymmetric extension of the standard model with CP-violation is considered in this paper. The main area of the model parameters, which is attractive for researchers, corresponds to small values of the tangent mixing angle of two doublets Higgs fields (tanβ). The authors discuss the possibilities of the model in correlation with the data on the search for the lightest stable supersymmetric particle. The masses of neutral Higgs bosons in the basis of CP-violationwas calculated.The results are presented as dependencies neutral CP-odd Higgs boson mass mA on tanβ. At small values tgβ the mass of the lightest stable particle must be more than ∼ 250 GeV.

Cross sections of fusion and transfer reactions in interactions between 3He and Pt and 197Au nuclei in the subbarrier energy region

The reactions of complete and incomplete fusion, along with nucleon transfer reactions in the range of 3He energies from 10 to 24.5 MeV, are investigated by irradiating gold and platinum targets with an accelerated 3He ion beam on the U-120M cyclotron at the Institute of Nuclear Physics, Czech Academy of Sciences, Řež. Activation is used to determine the yield of nuclides resulting from nuclear reactions. The γ-activity induced in the targets is measured using a with high-resolution HPGe detector. Despite the low binding energy of 3He and the reactions with positive Q values, the measured cross sections of fusion reactions exhibit no specific features, compared to reactions conducted using beams of other light stable particles. Transfer neutron reactions in the subbarrier energy region have relatively high cross sections. These cross sections continue to grow as the energy of 3He rises. When a neutron is captured by a nucleus of 3He, the cross sections of these reactions reach their maximum values in the Coulomb barrier region.

Fusion and transfer cross sections of 3He induced reaction on Pt and Au in energy range 10–24.5 MeV

In experiments performed by accelerated ion 3He-beam irradiated gold and platinum targets on the cyclotron U-120M of the Nuclear Physics Institute of the Czech Academy of Sciences, Řež, reactions of complete and incomplete fusion and nucleon transfer reactions in the 3He energy range from 10 to 24.5 MeV have been investigated. To determine the yield of the nuclides resulting from the nuclear reaction, the activation technique has been used. The obtained data are analyzed using models based on statistical calculations and compared with similar results for other light stable particles. Transfer reactions with positive Q values have relatively high cross sections in the energy range below the Coulomb barrier. These cross sections continue to grow with increasing 3He energy, and, in the case of capturing neutron from target nucleus by a nucleus of 3He, the excitation functions of these reactions reach their maximum almost at the Coulomb barrier of the reactions.

Search for a light neutralino of cosmological interest at the CERN LHC

We address the problem of a search at the LHC for a neutralino whose mass is around 10 GeV, i.e. in the range of interest for present data of direct search for dark matter particles in the galactic halo. This light neutralino is here implemented in an effective Minimal Supersymmetric extension of the Standard Model at the electroweak scale without requirement of a gaugino mass unification at a grand unification scale. In this model, light neutralinos that have the right cosmological properties and are able to explain current results of direct dark matter detection naturally arise. Within this model we identify a specific benchmark which maximizes chances of detection at the LHC, and we determine its prospects of reconstructing the main features of the light neutralino framework at different stages of the LHC runs. Our main result is that the LHC will hardly properly reconstruct the mass of such a light neutralino, due to the intrinsic difficulty in reconstructing the mass of light stable particles in relativistic events. However, the associated measurement of the mass of the heavier neutralinos allows us to point toward the right pattern of gaugino nonuniversality. Other relevant parameters of this model, like slepton and squark masses, can be reconstructed to a good level of precision.

Higgs funnel region of supersymmetric dark matter for smalltanβand renormalization group effects on pseudoscalar Higgs boson with scalar mass nonuniversality

A non-universal scalar mass supergravity type of model is explored where the first two generation of scalars and the third generation of sleptons may be very massive. Lighter or vanishing third generation of squarks as well as Higgs scalars at the unification scale cause the radiative electroweak symmetry breaking constraint to be less prohibitive. Thus, both FCNC/CP-violation problems as well as the naturalness problem are within control. We identify a large slepton mass effect in the RGE of $m_{H_D}^2$ (for the down type of Higgs) that may turn the later negative at the electroweak scale even for a small $\tan\beta$. A hyperbolic branch/focus point like effect is found for $m_A^2$ that may result in very light Higgs spectra. The lightest stable particle is dominantly a bino that pair annihilates via Higgs exchange, giving rise to a WMAP satisfied relic density region for all $\tan\beta$. Detection prospects of such LSPs in the upcoming dark matter experiments both of direct and indirect types (photon flux) are interesting. The Higgs bosons and the third generation of squarks are light in this scenario and these may be easily probed besides charginos and neutralinos in the early runs of LHC.

Probing new physics with long-lived charged particles produced by atmospheric andastrophysical neutrinos

As suggested by some extensions of the standard model of particle physics, dark mattermay be a super-weakly-interacting lightest stable particle, while the next-to-lightestparticle (NLP) is charged and metastable. One could test such a possibility with neutrinotelescopes, by detecting the charged NLPs produced in high-energy neutrino collisions withEarth matter. We study the production of charged NLPs by both atmospheric andastrophysical neutrinos; only the latter, which is largely uncertain and has not beendetected yet, was the focus of previous studies. We compute the resulting fluxes of thecharged NLPs, compare those of different origins and analyze the dependence on theunderlying particle physics set-up. We point out that, even if the astrophysicalneutrino flux is very small, atmospheric neutrinos, especially those from the promptdecay of charmed mesons, may provide a detectable flux of NLP pairs at neutrinotelescopes such as IceCube. We also comment on the flux of charged NLPs expectedfrom proton–nucleon collisions and show that, for theoretically motivated andphenomenologically viable models, it is typically subdominant and below detectablerates.

Mesons and diquarks in the color neutral superconducting phase of dense cold quark matter

The spectrum of meson and diquark excitations of dense color neutral cold quark matter is investigated in the framework of a two-flavored Nambu--Jona-Lasinio--type model, including a quark $\ensuremath{\mu}$- and color ${\ensuremath{\mu}}_{8}$-chemical potential. It was found that, in the color superconducting (2SC) phase, i.e. at $\ensuremath{\mu}>{\ensuremath{\mu}}_{c}=342\text{ }\text{ }\mathrm{MeV}$, ${\ensuremath{\mu}}_{8}$ acquires rather small values $\ensuremath{\sim}10\text{ }\text{ }\mathrm{MeV}$ in order to ensure the color neutrality. In this phase the $\ensuremath{\pi}$ and $\ensuremath{\sigma}$ meson masses are evaluated around $\ensuremath{\sim}330\text{ }\text{ }\mathrm{MeV}$. The spectrum of scalar diquarks in the color neutral 2SC phase consists of a heavy [${\mathrm{SU}}_{c}(2)$-singlet] resonance with mass $\ensuremath{\sim}1100\text{ }\text{ }\mathrm{MeV}$, four light diquarks with mass $3|{\ensuremath{\mu}}_{8}|$, and one Nambu-Goldstone boson, which is in accordance with the Goldstone theorem. Moreover, in the 2SC phase there are five light stable particles as well as a heavy resonance in the spectrum of pseudoscalar diquarks. In the color symmetric phase, i.e. for $\ensuremath{\mu}<{\ensuremath{\mu}}_{c}$, a mass splitting of scalar diquarks and antidiquarks is shown to arise if $\ensuremath{\mu}\ensuremath{\ne}0$, contrary to the case of $\ensuremath{\mu}=0$, where the masses of scalar antidiquarks and diquarks are degenerate at the value $\ensuremath{\sim}700\text{ }\text{ }\mathrm{MeV}$. If the coupling strength in the pseudoscalar diquark channel is the same as in the scalar diquark one (as for QCD-inspired Nambu--Jona-Lasinio models), then in the color symmetric phase pseudoscalar diquarks are not allowed to exist as stable particles.

Dark matter from early decays

Two leading dark matter candidates from supersymmetry and other theories of physics beyond the standard model are WIMPs and weak scale gravitinos. If the lightest stable particle is a gravitino, then a WIMP will decay into it with a natural lifetime of order a month $\ensuremath{\sim}{M}_{\mathrm{pl}}^{2}/{M}_{\mathrm{weak}}^{3}$. We show that if the bulk of dark matter today came from decays of neutral particles with lifetimes of order a year or smaller, then it could lead to a reduction in the amount of small scale substructure, less concentrated halos and constant density cores in the smallest mass halos. Such beneficial effects may therefore be realized naturally, as discussed by Cembranos, Feng, Rajaraman, and Takayama, in the case of supersymmetry.

Photinos from cosmic sources

In supersymmetric (SUSY) theories1, the photino is the fermion partner of the photon and is expected to be the lightest stable particle. Despite many discussions of the possible production of photinos, and other supersymmetric particles, at existing and proposed accelerators2, so far, experiments have only set limits3,4. We propose here that photinos are produced by sources of ultra-high-energy cosmic rays. We specifically consider Cygnus X-3, which is a powerful source of neutral particles up to 104 TeV (refs 5–8). These are usually assumed to be γ rays, but there is no direct evidence for this, and shower5,6 and underground9,10 experiments suggest that there may be another component present. Here we estimate that a photino flux of the order of 10−14 cm−2 s−1 above 10 TeV is possible from a source such as Cyg X-3, under certain conditions, and consider the feasibility of detecting these photinos.

Nonlinear Spinor Field

A nonlinear spinor field, suggested by the symmetric coupling between nucleons, muons, and leptons, has been investigated in the classical approximation. Solutions of the field equations having simple angular and temporal dependence were obtained, subject to the boundary conditions that the fields be regular and that all observable integrals be finite. These b.c. lead to a nonlinear eigenvalue problem, whose solutions may be systematically discussed in the phase plane. Numerical solutions were obtained with a differential analyzer. If charge and mass of the particle-like solutions are defined in terms of $\ensuremath{\int}{s}_{4}d\mathbf{x}$ and $\ensuremath{\int}{T}_{44}d\mathbf{x}$, then the number of masses corresponding to the same charge turns out to be small in all cases investigated. For certain lagrangians the nonlinearity leads to solutions having positive energy only. The mass ratio between the lightest stable particle and the heaviest unstable particle can be taken of the order of ${10}^{\ensuremath{-}3}$, if the nonlinear coupling constant is properly chosen. Although our specific model is too simple to meet certain obvious requirements, a theory of this general type has some interesting features.