Terms Of Annihilation Research Articles

Gupta-Bleuler quantization of the anisotropic parity-even andCPT-even electrodynamics of a standard model extension

We have established the Gupta-Bleuler quantization of the photon belonging to the anisotropic parity-even sector of the CPT-even and Lorentz-violating nonbirefringent electrodynamics of the standard model extension. We first present a rule for the Maxwell electrodynamics to be successfully quantized via Gupta-Bleuler technique in the Lorentz gauge. Recognizing the failure of the Gupta-Bleuler method in the Lorentz gauge, $\partial _{\mu }A^{\mu }=0$, for this massless LV theory, we argue that Gupta-Bleuler can be satisfactorily implemented by choosing a modified Lorentz condition, $\partial _{\mu }A^{\mu }+\kappa ^{\mu \nu }\partial _{\mu }A_{\nu }=0$, where $\kappa ^{\mu \nu }$ represents the Lorentz-violation in photon sector. By using a plane-wave expansion for the gauge field, whose polarization vectors are determined by solving an eigenvalue problem, and a weak Gupta-Bleuler condition, we obtain a positive-energy Hamiltonian in terms of annihilation and creation operators. The field commutation relation is written in terms of modified Pauli-Jordan functions, revealing the preservation of microcausality for sufficiently small LV parameters.

Disjunctive Ideals of Distributive Lattices

Disjunctive ideals and strongly disjunctive ideals are introduced in lattices and normal lattices are also characterized in terms of annihilators. Some properties of disjunctive ideals are studied. The concept of normal prime ideals is introduced and their properties are studied. Some equivalent conditions are derived for the class of all strongly disjunctive ideals to become a sublattice of the ideal lattice.

Development a dislocation density based model considering the effect of stacking fault energy: Severe plastic deformation

Considering the effect of an intrinsic material parameter, stacking fault energy (SFE), a model based on dislocation density is developed to investigate the evolutions of dislocation density, cell size and flow stress during severe plastic deformation of aluminum and nickel. In fact a model is presented considering the work hardening and different annihilation mechanisms for dislocation densities in cell interiors and cell walls. Annihilation terms are developed on the basis of SFE through the model. The calculations show that the total dislocation density, dislocation density in cell interiors, dislocation density in cell walls and flow stress are decreased with increasing SFE. To verify the model results, they are compared with the experimental data and a good agreement is observed.

Structural effects of energy input during growth of Ti1 − xAlxN (0.55 ≤ x ≤ 0.66) coatings by cathodic arc evaporation

Effects of growth conditions on structural properties are investigated for the case of Ti1−xAlxN (0.55≤x≤0.66) deposition by cathodic arc evaporation. The evolution of residual stress, stress free lattice parameter, crystalline content, grain size, growth rate, and ion irradiation is studied as functions of the following parameters: Al content, process temperature, substrate bias potential, arc current, and magnetic field in front of the cathode.The evolution of residual stress is explained in terms of generation and annihilation of defects. Generation of defects, as indicated by increased compressive stress and stress free lattice parameter, is found to be directly connected to an increased ion energy caused by either higher bias potential or increased (estimated) average charge state of the depositing species. Annihilation of defects, indicated by decreased compressive stress and stress free lattice parameter, is observed as process temperature or arc current is raised, where the effect of arc current becomes stronger at higher magnetic field strength. It is concluded that the most likely explanation is thermal activation caused, directly or indirectly, by the applied process parameters.The results also show a strong decrease in grain size as either of the studied parameters is increased. The grain refinement is found to be correlated to an increase in the amount of wurtzite phase, in addition to the majority NaCl phase, as detected by X-ray diffraction. It is proposed that the probability of forming wurtzite becomes higher as either the energy available increases (due to thermal activation) or the energetic difference between the two phases becomes smaller (e.g., as the Al content is increased from x=0.55 to x=0.66). This explanation is consistent with the evolution of grain size and phase content as functions of process conditions or Al content, and is further supported by the results on residual stress evolution.

Constraints on dark matter annihilation from AMS-02 results

We use recently released data on the positron-to-electron ratio in cosmic rays from the AMS-02 experiment to constrain dark matter annihilation in the Milky Way. Due to the yet unexplained positron excess, limits are generally weaker than those obtained using other probes, especially gamma rays. This also means that explaining the positron excess in terms of dark matter annihilation is difficult. Only if very conservative assumptions on the dark matter distribution in the Galactic Center region are adopted, it may be possible to accommodate dark matter annihilating to leptons with a cross section above 10^-24 cm^3/sec. We comment on several theoretical mechanisms to explain such large annihilation cross sections.

Offset of the dark matter cusp and the interpretation of the 130 GeV line as a dark matter signal

We show that the cusp in the dark matter (DM) distribution required to explain the recently found excess in the gamma-ray spectrum at energies ~130 GeV in terms of the DM annihilations cannot survive the tidal forces if it is offset by ~1.5^\circ from the Galactic centre as suggested by observations.

Photonic measures of helicity: optical vortices and circularly polarized reflection

For both paraxial and nonparaxial light, numerous electromagnetic quantities are expressible in terms of photon annihilation and creation operators. Accordingly, measures of energy, angular momentum, and chirality acquire a consistent interpretation. From the photonic nature of light, it emerges that an infinite hierarchy of spin-type measures depend on a difference in number operators for modes of opposing helicity, with pure circular polarization giving maximal values. Measures of orbital angular momentum are determined by a sum of corresponding number operators. Analysis of the electric and magnetic fields in the reflection of circular polarizations reveals regions of prominent chiral interference.

Branching Fractions andCPAsymmetries ofB→K0*1430ρωandB→K0*1430ϕDecays in the Family NonuniversalZ′Model

Within the QCD factorization framework, we investigate the branching fractions and the directCPasymmetries of decaysB→K0*1430ρωandB→K0*1430ϕunder two different scenarios in the standard model and the family nonuniversalZ′model. We find that the annihilation terms play crucial roles in these decays and lead to the major uncertainties. For decaysB-→K0*-1430ρ0ω, the newZ′boson could change the branching fractions remarkably. However, for other decays, its contribution might be clouded by large uncertainties from annihilations. Unfortunately, neither the standard model nor theZ′model can reproduce all experimental data simultaneously under one certain scenario. We also noted that the directCPasymmetries ofB-→K0*-1430ρ0ωcould be used to identify theK0*1430meson and search for the contribution of newZ′boson.

Stability of the Fe3 + state in ZnO

We have applied implantation of radioactive 57Mn + (T1/2 = 1.5 min) at the ISOLDE facility at CERN with 50–60 keV energy to fluences 760 K or storage at room temperature for 12 months, after which they show dominantly the Fe2 + state for <2 × 101057Mn/cm2 implantations. These findings are discussed in terms of diffusion and/or annihilation of implantation-induced defects.

VERITAS deep observations of the dwarf spheroidal galaxy Segue 1

The VERITAS array of Cherenkov telescopes has carried out a deep observational program on the nearby dwarf spheroidal galaxy Segue 1. We report on the results of nearly 48 hours of good quality selected data, taken between January 2010 and May 2011. No significant $\gamma$-ray emission is detected at the nominal position of Segue 1, and upper limits on the integrated flux are derived. According to recent studies, Segue 1 is the most dark matter-dominated dwarf spheroidal galaxy currently known. We derive stringent bounds on various annihilating and decaying dark matter particle models. The upper limits on the velocity-weighted annihilation cross-section are $\mathrm{<\sigma v >^{95% CL} \lesssim 10^{-23} cm^{3} s^{-1}}$, improving our limits from previous observations of dwarf spheroidal galaxies by at least a factor of two for dark matter particle masses $\mathrm{m_{\chi}\gtrsim 300 GeV}$. The lower limits on the decay lifetime are at the level of $\mathrm{\tau^{95% CL} \gtrsim 10^{24} s}$. Finally, we address the interpretation of the cosmic ray lepton anomalies measured by ATIC and PAMELA in terms of dark matter annihilation, and show that the VERITAS observations of Segue 1 disfavor such a scenario.

Dark matter interpretations of the cosmic-ray e ± excesses

The cosmic-ray excess observed by PAMELA in the positron fraction and by FERMI and HESS in e−+e+ can be interpreted in terms of dark matter annihilations or decays. We summarize the main possibilities and their possible tests.

Critique of generalised purity as an entanglement measure: Explicit failure in simple separable Bose–Hubbard models

The SU(2) and SU(3) Lie algebras lend themselves naturally to studies of two- and three-well Bose–Einstein condensates, with the group operators being expressed in terms of bosonic annihilation and creation operators at each site. The success of these representations has led to the purities associated with these algebras to be promoted as a measure of entanglement in these systems. In this work, we show that these purities do not provide an unambiguous measure of entanglement between wells, but instead give results which depend on the quantum statistical states of the atomic ensembles in each well. Using the example of totally uncoupled wells where the atoms in one have never interacted with the atoms in the other, we quantify these purities for different states and show that completely separable states can give values which have been claimed to indicate the presence of entanglement. We also consider claims that the generalised purities measure particle rather than mode entanglement, with emphasis on the case of indistinguishable bosons, as found in these systems.

The PAMELA space mission for antimatter and dark matter searches in space

The PAMELA satellite-borne experiment has presented new results on cosmic-ray antiparticles that can be interpreted in terms of DM annihilation or pulsar contribution. The instrument was launched from the Baikonur cosmodrome and it has been collecting data since July 2006. The combination of a permanent magnet silicon strip spectrometer and a silicon-tungsten imaging calorimeter allows precision studies of the charged cosmic radiation to be conducted over a wide energy range with high statistics. The primary scientific goal is the measurement of the antiproton and positron energy spectrum in order to search for exotic sources. PAMELA is also searching for primordial antinuclei (anti-helium), and testing cosmic-ray propagation models through precise measurements of the antiparticle energy spectrum and precision studies of light nuclei and their isotopes. This talk illustrates the most recent scientific results obtained by the PAMELA experiment.

Dark Matter, Cosmic Rays and Neutrinos: status circa 2010

Dark Matter constitutes more that 80% of the total amount of matter in the Universe, yet almost nothing is known about its nature. A powerful investigation technique is that of searching for the products of annihilations of Dark Matter particles in the galactic halo, on top of the ordinary cosmic rays. Recent data from the PAMELA and FERMI satellites and a number of balloon experiments have reported unexpected excesses in the measured fluxes of cosmic rays. Are these the first direct evidences for Dark Matter? If yes, which DM models and candidates can explain these anomalies (in terms of annihilations) and what do they imply for future searches and model building? What are the constraints from gamma rays and neutrino measurements?

Dark Matter Searches with Astroparticle Data

The existence of dark matter (DM) was first noticed by Zwicky in the 1930s, but its nature remains one of the great unsolved problems of physics. A variety of observations indicate that it is nonbaryonic and nonrelativistic. One of the preferred candidates for nonbaryonic DM is a weakly interacting massive particle (WIMP) that in most models is stable. WIMP self-annihilation can produce cosmic rays, gamma rays, and other particles with signatures that may be detectable. Hints of anomalous cosmic-ray spectra found by recent experiments, such as PAMELA, have motivated interesting interpretations in terms of DM annihilation and/or decay. However, these signatures also have standard astrophysical interpretations, so additional evidence is needed in order to make a case for detection of DM annihilation or decay. Searches by the Fermi-LAT for gamma-ray signals from clumps, nearby dwarf spheroidal galaxies, and galaxy clusters have also been performed, along with measurements of the diffuse Galactic and extragalactic gamma-ray emission. In addition, Imaging Air Cherenkov Telescopes like HESS, MAGIC, and VERITAS have reported on searches for gamma-ray emission from dwarf galaxies. In this review, we examine the status of searches for particle DM by these instruments and discuss the interpretations and resulting DM limits.

Understanding cosmic rays and searching for exotic sources with PAMELA

The instrument PAMELA, in orbit since 15 June 2006 on board of the Russian satellite Resurs DK1, is de- signed to study charged particles in the cosmic radiation, with a particular focus on antimatter and signals of dark mat- ter annihilation. PAMELA is also looking for primordial antinuclei, measuring light nuclei energy spectra, studying the mechanisms of acceleration and propagation of the cos- mic rays in the Galaxy, and monitoring the solar activity and the radiation belts. A review of the main experimental results obtained by PAMELA is presented in this paper. The observed anoma- lous positron excess is discussed in terms of annihilation of dark matter particles as well as in terms of standard astro- physical sources. Moreover constraints on dark matter mod- els from antiproton data are shown.

Observational constraints on interacting dark matter model without dark energy

The interacting dark matter (IDM) scenario allows for the acceleration of the Universe without Dark Energy. We constrain the IDM model by using the newly revised observational data including $H(z)$ data and Union2 SNe Ia via the Markov chain Monte Carlo method. When mimicking the $\Lambda$CDM model, we obtain a more stringent upper limit to the effective annihilation term at $\kappa C_1\approx 10^{-3.4}\rm{Gyr}^{-1}$, and a tighter lower limit to the relevant mass of Dark Matter particles at $M_x\approx 10^{-8.6}\rm{Gev}$. When mimicking the $w$CDM model, we find that the effective equation of state of IDM is consistent with the concordance $\Lambda$CDM model and appears to be most consistent with the effective phantom model with a constant EoS for which $w<-1$.

Dark matter interpretation of the origin of non-thermal phenomena in galaxy clusters

(Abridged) We study the predictions of various annihilating Dark Matter (DM) models in order to interpret the origin of non-thermal phenomena in galaxy clusters. We consider three neutralino DM models with light (9 GeV), intermediate (60 GeV) and high (500 GeV) mass. The secondary particles created by neutralino annihilation produce a multi-frequency Spectral Energy Distribution (SED), as well as heating of the intracluster gas, that are tested against the observations available for the Coma cluster. The DM produced SEDs are normalized to the Coma radio halo spectrum. We find that it is not possible to interpret all non-thermal phenomena observed in Coma in terms of DM annihilation. The DM model with 9 GeV mass produces too small power at all frequencies, while the DM model with 500 GeV produces a large excess power at all frequencies. The DM model with 60 GeV and $\tau^{\pm}$ composition is consistent with the HXR and gamma-ray data but fails to reproduce the EUV and soft X-ray data. The DM model with 60 GeV and $b{\bar b}$ composition is always below the observed fluxes. The radio halo spectrum of Coma is well fitted only in the $b{\bar b}$ or light and intermediate mass DM models. The heating produced by DM annihilation in the center of Coma is always larger than the intracluster gas cooling rate for an NFW DM density profile and it is substantially smaller than the cooling rate only for a cored DM density profile in DM model with 9 GeV. We conclude that the possibility of interpreting the origin of non-thermal phenomena in galaxy clusters with DM annihilation models requires a low neutralino mass and a cored DM density profile. If we then consider the multimessenger constraints to the neutralino annihilation cross-section, it turns out that such scenario would also be excluded unless we introduce a substantial boost factor due to the presence of DM substructures.

Black holes in our galactic halo: compatibility with FGST and PAMELA data and constraints on the first stars

10−105m☉ black holes with dark matter spikes that formed in early minihalos and still exist in our Milky Way Galaxy today are examined in lightof recent data from the Fermi Gamma-Ray Space Telescope (FGST). The dark matter spikes surrounding black holes in our Galaxy are sites of significant dark matter annihilation. We examine the signatures of annihilations into gamma-rays, e+/e−,and neutrinos. We find that some significant fraction of the point sources detected by FGST might be due to dark matter annihilation near black holes in our Galaxy. We obtain limits on the properties of dark matter annihilations in the spikes using the information in the FGST First Source Catalog as well as the diffuse gamma-ray flux measured by FGST.We determine the maximum fraction of high redshift minihalos that could have hosted the formation of the first generation of starsand, subsequently, their black hole remnants. The strengthof the limits depends on the choice ofannihilation channel and black hole mass; limits are strongest for the heaviest black holes andannhilation to bb̄ and W+W− final states. The larger black holes considered in this paper may arise as the remnants of Dark Stars after the dark matter fuel is exhausted and thermonuclear burning runs its course; thus FGST observations may be used to constrain the properties of Dark Stars. Additionally, we comment on the excess positron flux found by PAMELA and its possible interpretation in terms of dark matter annihilation around these black hole spikes.

Dark matter in natural supersymmetric extensions of the standard model

We explore the dark matter sector in extensions of the minimal supersymmetric standard model that can provide a good fit to the PAMELA cosmic-ray positron excess, while at the same time addressing the little-hierarchy problem of the minimal supersymmetric standard model. Adding a singlet Higgs superfield $S$ can account for the observed positron excess, as recently discussed in the literature, but we point out that it requires a fine-tuned choice for the parameters of the model. We find that including an additional singlet $\ensuremath{\Psi}$ in a model with gauge-mediated supersymmetry breaking is a minimal extension which allows both a reduction of the weak-scale fine-tuning and an interpretation of the cosmic-ray observations in terms of dark matter annihilations in the galactic halo. Our setup contains a light axion but does not require light $CP$-even scalars in the spectrum.