Narrow Results

We examine dark matter annihilation in the Universe today. We first discuss the suggestion that the Galactic positron flux, which is difficult to account for with astrophysical sources, is produced by the annihilation of dark matter in the Galactic halo. We show that the positrons produced would necessarily be accompanied by a flux of gamma rays which exceed observational constraints, unless the dark matter mass is very low. We shall also derive a very general bond on the dark matter annihilation cross section. By considering annihilation into all Standard Model particles, we show that the least detectable final states, namely neutrinos, define an upper bound on the total annihilation cross section. Calculating the cosmic diffuse neutrino signal, and comparing it to the measured terrestrial atmospheric neutrino background, we derive a robust limit that is much stronger than the unitarity bound in the most interesting mass range. We conclude that dark matter self-annihilation rates cannot be large enough to have a significant effect on the density profiles of dark matter halos.

Recently data from PAMELA, ATIC, FERMI-LAT and HESS show that there are e^± excesses in the cosmic ray energy spectrum. PAMELA shown excesses only in e⁺, but not in anti-proton spectrum. ATIC, FERMI-LAT and HESS shown excesses in e⁺+e^- spectrum, but the detailed shapes are different which requires future experimental observations to pin down the correct data set. Nevertheless a lot of efforts have been made to explain the observed e^± excesses, and also why PAMELA only has excesses in e⁺ but not in anti-proton. In this brief review we discuss one of the most popular mechanisms to explain the data — the dark matter annihilation. It has long been known that about 23% of our universe is made of relic dark matter. If the relic dark matter was thermally produced, the annihilation rate is constrained resulting in the need of a large boost factor to explain the data. We will discuss in detail how a large boost factor can be obtained by the Sommerfeld and Breit–Wigner enhancement mechanisms. Some implications for particle physics model buildings will also be discussed.

Using the Gammasphere array of high-purity germanium detectors at the 88" Cyclotron at Lawrence Berkeley National Laboratory, we have made several measurements to test discrete fundamental symmetries in positronium annihilation. We tested charge conjugation symmetry (C) by searching for decays of ortho- and para-positronium to the "wrong" number of photons. We measured the five-photon annihilation mode of ortho-positronium, finding agreement with tree-level QED calculations at order α⁸. In a second experiment, we searched for decays of polarized ortho-positronium which violate the combined symmetry operation CPT. We improved existing limits on this CPT test by roughly a factor of ten. We are studying the feasibility of an experiment to search for "invisible" decays of ortho-positronium. Invisible decays could be caused by extra dimensions (invoked in string theories). General requirements for an experiment sensitive to decay branching ratios of order 10^-9 are discussed.

The energy and momentum conservation laws prohibit positron–electron single-photon annihilation in vacuum. It is shown that the situation is different in a single crystal with one of the leptons (e.g. positron) moving in the channeling (or in the quasi-channeling) mode. The transverse motion of an oriented or channeled particle may sharply increase the probability of the single-photon annihilation process.

We show that due to the large coupling constant of the monopole–photon interaction the annihilation of monopole–antimonopole and monopolium into many photons must be considered experimentally. For monopole–antimonopole annihilation and lightly bound monopolium, even in the less favorable scenario, multiphoton events (four and more photons in the final state) are dominant, while for strongly bound monopolium, although two photon events are important, four- and six-photon events are also sizable.

Experiments with antiprotons often require the tracking of charged particles emerging from the annihilation process. The Atomic Spectroscopy And Collisions Using Slow Antiprotons (ASACUSA) collaboration at the CERN Antiproton Decelerator (AD) used several panels of scintillating bars placed around the interaction region to detect the passage of charged pions and determine the annihilation vertex position and time. The panels were composed by extruded scintillating bars and the light was collected using WaveLength Shifting (WLS) fibers and multi-anode PhotoMultiplier Tubes (PMTs). After operating for several years, the fiber-PMT coupling quality had degraded and a major upgrade of the light readout system was planned. The PMTs will be replaced by Silicon PhotoMultipliers (SiPMs) and the front-end electronics changed accordingly. An improvement is expected in the efficiency and the uniformity of the detector response. In this contribution the commissioning of the upgrade will be described, including the results of preliminary tests with cosmic rays.

In this work, we present the conducted studies for the production of the monopolium at the LHC in ultraperipheral collisions, using beams of proton–proton (pp) and lead–lead (PbPb) nuclei. The monopolium is the bound state of a monopole–antimonopole pair. The study of the magnetic monopole in this characteristic state is justified due to the very strong coupling constant, which allows us to suggest that this exotic particle can be produced in the bound state. In this approach, the monopolium is described by a wave function, and its solution comes from the numerical method applied to the Schrödinger equation with a modified Cornell potential. The monopolium is produced by a photon fusion production mechanism, with the Weizsäcker–Williams and Drees–Zeppenfeld expressions to describe the lead and proton equivalent photon distributions. We estimate a high-production rate of monopolium for pp collisions with $\sqrt{s}=14$TeV and PbPb collisions with $\sqrt{s}=5.5$TeV at the LHC.

Using an extended mapping approach and a special Painlevé–Bäcklund transformation, respectively, we obtain two families of exact solutions to the (2+1)-dimensional Boiti–Leon–Martina–Pempinelli (BLMP) system. In terms of the derived exact solution, we reveal some novel evolutional behaviors of localized excitations, i.e., fission, fusion, and annihilation phenomena in the (2+1)-dimensional BLMP system.

We have investigated the behavior of vortices in a polycrystalline YBa₂Cu₃O_7-δ disk sample using rotational magnetization-vector (RMV) measurements. The measurements were conducted in the field-cooled (FC) and the zero-field cooled (ZFC) states for several values of applied magnetic field parallel to the sample surface at 4.2 K and for various angles of rotation (θ_rot) up to 360°. The total magnetic flux density, B, in the sample at any rotational angle was considered to be composed of two types of vortices: weakly pinned vortices that rotate frictionally in the opposite direction of sample rotation and strongly pinned vortices that rotate rigidly in the same direction of sample rotation. From the rate of change of these two types of vortices and the rate of change of B, we were able to develop a tool to qualitatively describe the average strength of pinning centers in high-temperature superconductors.

We study the propagation of nonlinear waves in a three-component reaction–diffusion system. The problem of the existence of the stationary pulse-like solutions is reduced to the analysis of homoclinic trajectories of a fourth-order system of nonlinear ODEs. We have obtained the parameter set corresponding to the homoclinic bifurcations that defines the velocity spectra of the traveling pulses. We have shown that the pulses behave like autowaves annihilating in head-on collision and like dissipative solitons crossing each other, reflecting at boundaries. We have provided a qualitative explanation for such a behavior.

An infection spreads in a binary tree of height n as follows: initially, each leaf is either infected by one of k states or it is not infected at all. The infection state of each leaf is independently distributed according to a probability vector p = (p₁, …, p_k+1). The remaining nodes become infected or not via annihilation and coalescence: nodes whose two children have the same state (infected or not) are infected (or not) by this state; nodes whose two children have different states are not infected; nodes such that only one of the children is infected are infected by this state. In this paper we characterize, for every p, the limiting distribution at the root node of as n goes to infinity.

We also consider a variant of the model when k = 2 and a mutation can happen, with a fixed probability q, at each infection step. We characterize, in terms of p and q, the limiting distribution at the root node of as n goes to infinity.

The distribution at the root node is driven by a dynamical system, and the proofs rely on the analysis of this dynamics.

We prove, for all quadratic and a wide range of multi-quadratic extensions of global fields, a result concerning the annihilation as Galois modules of ideal class groups by explicit elements constructed from the values of higher-order derivatives of Dirichlet L-functions. This result simultaneously refines Rubin's integral version of Stark's Conjecture and provides evidence for the relevant case of the Equivariant Tamagawa Number Conjecture of Burns and Flach.

We perform a fitting procedure to differential elastic scattering cross section data of antiproton at intermediate energy on three different nuclei to evaluate parameters of a six-parameters Woods-Saxon optical potential. Then, with these values, we calculate the reaction cross sections at different momenta and evaluate the differential elastic cross sections for low-momenta antiproton ($p\le 100\mathrm{\text{MeV/c}}$). We find that our analysis underestimates the reaction cross sections for data over the momentum-range 50 MeV/c to 1000 MeV/c. We predict measurable effect for antiprotons with momentum above 50 MeV/c at large angles ($𝜃>90°$), in agreement with other recent results. Finally, we consider possible improvements to the model and the analysis.

The quantum operators generated by a random variable X, having finite moments of all orders, are expressed as a sum of compositions of powers of the multiplication operator by X and differentiation operator D = d/dX. The multiplication by X operator is located to the left of the differentiation operator.

It is described the distribution of small-scale dark matter (DM) clumps in the Galactic halo. These clumps are efficiently destructed by tidal forces at early stages of structure formation starting from time of clump detachment from the expansion of the Universe. Only a small fraction of these clumps survives the stage of hierarchical clustering. The survived clumps can be further destructed in the Galaxy by tidal interactions with stars in the Galactic bulge, disk and halo. It is shown that collective gravitational field of the Galactic disc provides the dominant contribution to the destruction of small-scale clumps. The resulting enhancement (boost factor) of annihilation signal due to the halo clumpiness strongly depends on the primordial perturbation spectrum and varies in the range 10-100.

In classical electrodynamics, extended with gradients of the electric and magnetic fields, a linear soliton is presented which bears features of the Kerr-Newman electron of electro-gravity. This is considered as a model for the electron, having a ring shape, with diameter equal to the Compton length ħ/mc and thickness smaller by the fine structure constant. The soliton has a finite mass, a spin-½, a g = 2 factor, and an electric quadrupole moment that is also “twice too large”. From this setup, all relativistic corrections to the classical version of the Pauli Hamiltonian are derived. There appears an additional, spin-dependent quadrupolar force that may vanish on the average. Particle-antiparticle annihilation may become explained on the basis of electromagnetic attraction.

The correlations of secondary pions in annihilation and non-annihilation channels are investigated.

We consider the annihilation of dark matter into Standard Model particles. We show that the least detectable annihilation products, namely neutrinos, can be used to set a conservative bound on the total annihilation cross section. This bound is much stronger than the unitarity bound for the most interesting mass range, and shows that dark matter halos cannot be significantly modified by annihilations. We also discuss the production of Galactic positrons via dark matter annihilation.

A simple method of recovering the moments of a probability measure, on ℝ, from the commutator between its annihilation and creation operators, the commutator between the annihilation and preservation operator, and the first moment is presented.

We use a high-resolution simulation of a galaxy-sized dark matter halo, published simulated data as well as four cluster-sized haloes¹ to study the inner halo structure in a Lambda cold dark matter cosmology. We find that the circular velocity curves are substantially better described by SWTS^2,3 profiles than by NFW⁴ or Moore⁵ profiles. Our findings confirm that no asymptotic slope is reached and that the corresponding extrapolated density profiles reach a finite maximum density. We analyse the impact of our findings on the detectability of the gamma-ray signal from the central regions of the Milky Way (MW) and from dark matter substructures in its halo, if the dark matter in the Universe is made of weakly self-interacting particles which self-annihilate. We discuss detection strategies for current gamma-ray detectors. We in addition review recent work by other authors and comment on possible boosts due to effects of structure on very small scales.