Neutral Scalar Particle Research Articles

STABLE AND DECAYING BOUND STATES ON THE NAKED REISSNER–NORDSTRÖM SPACETIME

We present a quantum mechanical study of the bound states of a neutral scalar particle on the curved background described by the Reissner–Nordström (RN) spacetime that corresponds to a naked singularity. We show that there occurs both the metastable, i. e. decaying bound states and the stable ones. The corresponding energy spectra are calculated in the leading WKB approximation and the comparison with RN black hole quasinormal mode spectrum is made. The metastable bound states on the naked singularity background turn out to be more long-living than the quasinormal modes for the black hole with the same mass.

Phenomenology of MaVaN’s Models in Reactor Neutrino Data

Mass Varying Neutrinos (MaVaN’s) mechanisms were proposed to link the neutrino mass scale with the dark energy density, addressing the coincidence problem. In some scenarios, this mass can present a dependence on the baryonic density felt by neutrinos, creating an effective neutrino mass that depends both on the neutrino and baryonic densities. In this work, we study the phenomenological consequence of MaVaN’s scenarios in which the matter density dependence is induced by Yukawa interactions of a light neutral scalar particle which couples to neutrinos and matter. Under the assumption of one mass scale dominance, we perform an analysis of KamLAND neutrino data which depends on 4 parameters: the two standard oscillation parameters,Δm0,212andtan2θ12, and two new coefficients which parameterize the environment dependence of neutrino mass. We introduce an Earth’s crust model to compute precisely the density in each point along the neutrino trajectory. We show that this new description of density does not affect the analysis with the standard model case. With the MaVaN model, we observe a first order effect in lower density, which leads to an improvement on the data description.

Can quantum mechanics fool the cosmic censor?

We revisit the mechanism for violating the weak cosmic-censorship conjecture (WCCC) by overspinning a nearly-extreme charged black hole. The mechanism consists of an incoming massless neutral scalar particle, with low energy and large angular momentum, tunneling into the hole. We investigate the effect of the large angular momentum of the incoming particle on the background geometry and address recent claims that such a backreaction would invalidate the mechanism. We show that the large angular momentum of the incident particle does not constitute an obvious impediment to the success of the overspinning quantum mechanism, although the induced backreaction turns out to be essential to restoring the validity of the WCCC in the classical regime. These results seem to endorse the view that the ``cosmic censor'' may be oblivious to processes involving quantum effects.

Enhanced rare pion decays from a model of MeV dark matter

A model has been proposed in which neutral scalar particles chi, of mass 1-10 MeV, annihilate through the exchange of a light vector boson U, of mass 10-100 MeV, to produce the 511 keV line observed emanating from the center of the galaxy. The chi interacts weakly with normal matter and is a viable dark matter candidate. If the U-boson couples to quarks as well as to electrons, it could enhance the branching ratio for the rare decay pi0 -> e+e-. A recent measurement by the KTeV Collaboration lies three standard deviations above a prediction by Dorokhov and Ivanov, and we relate this excess to the couplings of the U-boson. The values are consistent with other constraints and considerations. We make some comments on possible improvements in the data.

Littlest Higgs model and W pair production at international linear collider

Among the viable alternatives to the standard Higgs mechanism is the recently proposed Little Higgs model. The advantage here is that the model has an elementary light neutral scalar particle, which arises dynamically as against its ad hoc introduction in the standard model. The model also avoids hierarchy problem. We have investigated the W pair production at ILC to study the littlest Higgs model using different observables. Specifically, polarization fraction of W boson is expected to be measured very accurately at ILC. We use this to put limit on the scale parameter, f, in the model.

Effective 4D propagation of a charged scalar particle in Visser brane world

In this work we extend an analysis due to Visser of the effective propagation of a neutral scalar particle on a brane world scenario which is a particular solution of the five dimensional Einstein-Maxwell equations with cosmological constant having an electric field pointing in the extra spatial dimension. We determine the dispersion relations of a charged scalar particle to first order in a perturbative analysis around those of the neutral particle. Since depending on whether the particle is charged or not the dispersion relations change, we could collect bulk information, namely the presence of the electric field, by studying the 4D dynamics of the particles.

Unstable relics as a source of galactic positrons

We calculate the fluxes of 511 keV photons from the galactic bulge caused by positrons produced in the decays of relic particles with masses less than 100 MeV. In particular, we tighten the constraints on sterile neutrinos over a large domain of the mass-mixing angle parameter space, where the resulting photon flux would significantly exceed the experimental data. At the same time, the observed photon fluxes can be easily caused by decaying sterile neutrinos in the mass range 1<msterile≲50 MeV with the cosmological abundance typically within 10−9≲Ωsterile≲10−5, assuming that Ωsterile comes entirely from the conversion of active neutrinos in the early universe. Other candidates for decaying relics such as neutral (pseudo)scalar particles coupled to leptons with the gravitational strength can be compatible with the photon flux, and can constitute the main component of cold dark matter.

DarkSUSY: computing supersymmetric dark matter properties numerically

The question of the nature of the dark matter in the Universe remains one of the mostoutstanding unsolved problems in basic science. One of the best motivated particle physicscandidates is the lightest supersymmetric particle, assumed to be the lightestneutralino—a linear combination of the supersymmetric partners of the photon, theZ boson and neutral scalar Higgs particles. Here we describe DarkSUSY, a publicly available advanced numerical package for neutralino dark matter calculations.In DarkSUSY one can compute the neutralino density in the Universe today using precisionmethods which include resonances, pair production thresholds and coannihilations.Masses and mixings of supersymmetric particles can be computed within DarkSUSY or with the help of external programs such as FeynHiggs, ISASUGRA and SUSPECT.Accelerator bounds can be checked to identify viable dark matter candidates. DarkSUSY also computes a large variety of astrophysical signals from neutralino dark matter, such asdirect detection in low-background counting experiments and indirect detection throughantiprotons, antideuterons, gamma-rays and positrons from the galactic halo or high-energyneutrinos from the centre of the Earth or of the Sun. Here we describe the physics behindthe package. A detailed manual will be provided with the computer package.

Towards automatic analytic evaluation of diagrams with masses

A method to calculate two-loop self-energy diagrams of the Standard Model is demonstrated. A direct physical application is the calculation of the two-loop electroweak contribution to the anomalous magnetic moment of the muon 1 2 (g−2) μ . Presently, we confine ourselves to a “toy” model with only μ, γ and a heavy neutral scalar particle (Higgs). The algorithm is implemented as a FORM-based program package. For generating and automatically evaluating any number of two-loop self-energy diagrams, a special C program has been written. This program creates the initial FORM-expression for every diagram generated by QGRAF, executes the corresponding subroutines and sums up the final results.

Particle creation in the Bell - Szekeres spacetime

The quantization of a real massless scalar field in a spacetime produced in a collision of two electromagnetic plane waves with constant wavefronts is considered. The background geometry in the interaction region, the Bell - Szekeres solution, is locally isometric to the conformally flat Bertotti - Robinson universe filled with a uniform electric field. It is shown that before the waves interact the Bogoliubov coefficients relating different observers are trivial and no vacuum polarization takes place. In the non-singular interaction region neutral scalar particles are produced with the number of created particles and spectrum typical of gravitational wave collision.

Renormalization-group analysis of the Higgs sector in the minimal supersymmetric standard model

We examine the particle spectra of the Higgs sector in the minimal supersymmetric extension of the standard model using the one-loop renormalization group evolution of the scalar self-couplings. We treat the general case in which there are two light Higgs doublets below the soft supersymmetry breaking scale M SUSY. The model with only one light CP-even neutral scalar particle appears as a particular limiting case in our analysis. Using theoretical and experimental results, we obtain upper and lower bounds on the neutral CP-even and charged Higgs mass spectrum. The triviality bounds on the top and Higgs masses are also analyzed, yielding constraints on the range of mass parameters consistent with possible grand unification scenarios. We obtain that for an effective cutoff scale Λ ⋍ 10 16 GeV (10 10 Gev) , a soft supersymmetry breaking scale M SUSY ⋍ 1 TeV and a CP-odd state mass m A ⋍ 40 GeV , the lightest CP-even state mass is bounded to be m h ⩽ 52 GeV (60 GeV). In addition, for the same values of Λ and M SUSY, and for m A ⩾ M Z, the tree-level relation m h ⩽ m A is fulfilled. Our analysis indicates that, in the simplest grand unification scenarios with M GUT ⋍ 10 16 GeV and M SUSY ⋍ 1 TeV , the decay mode h → AA is only allowed if m A ⩽ 26 GeV.

LIMITS ON THE MASS OF LIGHT (PSEUDO)SCALAR PARTICLES FROM BETHE-HEITLER e+e− and μ+μ− PAIR PRODUCTION IN A PROTON-IRON BEAM DUMP EXPERIMENT

A search has been performed for weakly interacting neutral light scalar and pseudoscalar particles in a proton-iron beam dump experiment via the Bethe-Heitler process. No positive signal was observed. Limits are derived on the masses of these particles in the framework of the Standard Model and its minimal supersymmetric extension (MSSM) comparing the experimental results with expectations for Bethe-Heitler e+e− and μ+μ− pair production. The Higgs particle of the SU2L×U1 Standard Theory is excluded for masses in the range mH&lt;0.9 MeV at 95% CL. Limits on light Higgs particles of the MSSM and Peccei-Quinn like axions are derived.

Search for a light neutral boson associated with beta decay

A gamma-gamma coincidence measurement was performed in order to search for a neutral scalar particle associated with beta decay with a mass near 17 keV. The measurement used a 35S source and two LEPS-type Ge detectors. A coincidence signal above the background generated by random bremsstrahlung coincidences would be a signature of the two-photon decay of a light neutral scalar particle. No evidence was found for such a particle with a mass near 17 keV with a lifetime shorter than 1 nanosecond.

Excess of τ +τ - V events in Z decays A naive look

The ALEPH Collaboration has analyzed the decays Z→ℓ +ℓ − V (V = e +e −, μ + μ −, π + π −), where ℓ is a lepton (ℓ=e, μ, τ). A possible excess of events is observed when ℓ is the τ lepton. We find that the observed kinematic distributions can be reproduced by assuming that (i) a new vector boson S couples vectorially to the τ, and (ii) the vector boson S decays into a V (through virtual Z exchange) and a pair of neutral scalar particles ζ.

Limits on neutral light scalar and pseudoscalar particles in a proton beam dump experiment

A search has been performed for weakly interacting neutral light scalar and pseudoscalar particles in a proton beam dump experiment. No positive signal is observed. Limits on the mass and life-time of these particles are set in the frame of the Standard Model and its minimal supersymmetric extension. The Higgs particle of theSU2L×U1 Standard Theory is excluded for masses in the range 1 MeV<mH<80 MeV at 95%CL. Limits on the Peccei-Quinn like axions are derived.

Flavour mixing neutrino oscillations

The β spectrum recorded in a recent experiment is consistent with the emission of a heavy neutrino of mass about 17.1 keV and the mixing probability with the conventional massless neutrino is about 3%. This phenomenon appears as a manifestation of a new low-mass scale at which the global symmetry of lepton number is spontaneously broken. The model we introduce here in order to incorporate experimental data has been elaborated earlier by Gelmini and Roncadelli. Its remarkable feature is the presence of a massless neutral scalar particle known as majoron—the Goldstone boson of broken global symmetry. This majoron and a neutral Higgs with low-mass scalar also predicted appear coupled strongly to neutrinos and very weakly to quarks and leptons so that they cannot be detected at present laboratory energies. The neutrino observed by Simpson cannot be simply a Majorana particle, since this would imply that the neutrinoless double β-decay should go at a rate approximately 2000 times the present limit. This tends to suggest that neutrinos observed here are Dirac particles—components of a degenerate Majorana pair with oppositeCP eigenvalues giving net zero contribution to the double β-decay amplitude. This experiment by Simpson suggests that these neutrinos cannot be associated with the muon or the τ lepton. Our model contains one mixing angle and one mass parameter fixed by observation of Simpson in order to predict flavour mixing neutrino oscillations. A theoretical framework presented here states that the electron neutrino wave function ∣ve>L= sin θ oscillates with another neutrino of different flavour where ∣v1>L and ∣vn>L are massless and heavy neutrinos observed in tritium β-decay, respectively and the mixing angle sin θ is about 0.14÷0.20. Cosmological constraints on the 17 keV neutrino are discussed. Models with majorons or familons are found to be attractive possibilities.

Baryon-symmetric baryogenesis.

We propose a new scenario of baryogenesis in which baryon number is an exact symmetry of the fundamental Lagrangian. If the global U(1) symmetry associated with baryon number is spontaneously broken at early times (when the temperature was of order 1--100 GeV) then the out-of-equilibrium decay of baryonic scalar particles can yield a cosmic baryon asymmetry in ordinary matter. This baryon number is exactly compensated by antibaryon number in the vacuum. At low temperatures, the symmetry is restored, and the antibaryons show up as neutral (antibaryonic) scalar particles or as nontopological solitons.

Covariant light front perturbation theory and three-particle equations.

A covariant version of light front perturbation theory is obtained as a limit of the covariant time-ordered perturbation theory developed recently by the author. The graphical rules for the covariant light front perturbation theory are essentially the same as Weinberg's infinite momentum frame rules; however, they involve a redefinition of the original Weinberg variables. The new definitions guarantee that the contributions of individual diagrams to the S matrix are invariant. A set of manifestly invariant three-particle integral equations is derived. These equations are obtained from a model field theory which describes the interaction of a charged scalar particle \ensuremath{\psi} with a neutral scalar particle \ensuremath{\varphi} according to the virtual process \ensuremath{\psi}\ensuremath{\rightleftarrows}\ensuremath{\psi}+\ensuremath{\varphi}. The solutions of the integral equations lead to amplitudes for \ensuremath{\varphi}+\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\varphi}+\ensuremath{\psi} and \ensuremath{\varphi}+\ensuremath{\psi}\ensuremath{\rightarrow}2\ensuremath{\varphi}+\ensuremath{\psi} which satisfy two- and three-particle unitarity. The integral equations are free of the spurious singularity in s, the square of the invariant c.m. energy, which has been an undesirable feature of earlier relativistic three-particle equations. This singularity is known to be responsible for spurious bound state solutions.

Signatures for technicolor.

The present experimental constraints on the existence of light charged and neutral electroweak scalar particles are summarized. Within the context of an explicit extended technicolor model, we discuss prospects for the detection of light scalars in p\ifmmode\bar\else\textasciimacron\fi{}p collisions at energies up to 2 TeV, in ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ collisions at energies up to the ${Z}^{0}$ mass, and in fixed-target hadron-hadron collisions. In addition the production cross sections of the other expected scalars are computed and decay signatures are explored.

Limits on light higgs bosons from the decays [formula omitted

Current experimental limits on K ±→ π ±e −e + rule out a neutral scalar particle with the couplings of the standard Higgs boson and mass in the range 50 MeV to 211 MeV. Planned experimental improvements could lead to a bound m H ⩾ m K− m π .