We use high resolution numerical simulations of the formation of cold dark matter halos to simulate the background of decay products from neutralino annihilation, such as gamma-rays or neutrinos. Halos are non-spherical, have steep singular density profiles and contain many thousands of surviving dark matter substructure clumps. This leads to several unique signatures in the gamma-ray background that may be confirmed or rejected by the next generation of gamma-ray experiments. Most importantly, the diffuse background is enhanced by over two orders of magnitude due to annihilation within substructure halos. The largest dark substructures are easily visible above the background and may account for the unidentified Energetic Gamma Ray Experiment Telescope ͑EGRET͒ sources. A deep strip survey of the gamma-ray background would allow the shape of the galactic halo to be quantified. PACS number͑s͒: 98.35.Gi, 95.35.ϩd, 95.75.Pq, 95.85.Pw *

We use a cosmological simulation of the Local Group to make quantitative and speculative predictions for direct detection experiments. Cold dark matter (CDM) halos form via a complex series of mergers, accretion events and violent relaxation which precludes the formation of significant caustic features predicted by axially symmetric collapse. The halo density profiles are combined with observational constraints on the galactic mass distribution to constrain the local density of cold dark matter to lie in the range 0.18 ∼ < ρ CDM (R⊙)/(GeV cm −3 ) ∼ < 0.30. In velocity space, coherent streams of dark matter from tidally disrupted halos fill the halo and provide a tracer of the merging hierarchy. The particle velocities within triaxial CDM halos cannot be approximated by a simple Maxwellian distribution and is radially biased at the solar position. The detailed phase space structure within the solar system will depend on the early merger history of the progenitor halos and the importance of major mergers over accretion dominated growth. We follow the formation of a "Draco" sized dSph halo of mass 10 8 M⊙ with several million particles and high force accuracy. Its internal structure and substructure resembles that of galactic or cluster mass halos: the density profile has a singular central cusp and it contains thousands of sub-halos orbiting within its virial radius demonstrating a self-similar nature to collisionless dark matter sub-clustering. The singular cores of substructure halos always survive complete tidal disruption although mass loss is continuous and rapid. Extrapolating wildly to earth mass halos with velocity dispersion of 1 m s −1 (roughly equal to the free streaming scale for neutralinos) we find that most of the dark matter may remain attached to bound subhalos. Further numerical and analytic work is required to confirm the existence of a detectable smooth component. PACS number(s): 95.35.+d, 98.35.Gi, 98.35.Df, 98.35.Mp, 95.75.Pq

Deep images of the Centaurus and Coma clusters reveal two spectacular arcs of diffuse light that stretch for over 100 kpc, yet are just a few kpc wide. At a surface brightness of m_b \sim 27-28th arcsec^-2, the Centaurus arc is the most striking example known of structure in the diffuse light component of a rich galaxy cluster. We use numerical simulations to show that the Centaurus feature can be reproduced by the tidal debris of a spiral galaxy that has been tidally disrupted by the gravitational potential of NGC 4709. The surface brightness and narrow dimensions of the diffuse light suggest that the disk was co-rotating with its orbital path past pericentre. Features this prominent in clusters will be relatively rare, although at fainter surface brightness levels the diffuse light will reveal a wealth of structure. Deeper imaging surveys may be able to trace this feature for several times its presently observed extent and somewhere along the tidal debris, a fraction of the original stellar component of the disk will remain bound, but transformed into a faint spheroidal galaxy. It should be possible to confirm the galactic origin of the Centaurus arc by observing planetary nebulae along its length with redshifts close to that of NGC 4709.Comment: Replaced with version accepted by MNRAS (Dec. 1999): Added missing reference (to pg. 4 & reference list). Section 3 shortened; removed three figures. Now 8 pages long, with 8 figures. Low resolution images included, high resolution version available at http://star-www.dur.ac.uk:80/~calcaneo/cenarc.htm

We demonstrate that in unquenched quantum electrodynamics (QED), chiral symmetry breaking ceases to exist above a critical number of fermion flavors N f . This is a necessary and sufficient consequence of the fact that there exists a critical value of electromagnetic coupling beyond which dynamical mass generation gets triggered. We employ a multiplicatively renormalizable photon propagator involving leading logarithms to all orders in to illustrate this. We study the flavor and coupling dependence of the dynamically generated mass analytically as well as numerically. We also derive the scaling laws for the dynamical mass as a function of and N f . Up to a multiplicative constant, these scaling laws are related through ð; c Þ $ ð1=N f ; 1=N c f Þ. Calculation of the mass anomalous dimension m shows that it is always greater than its value in the quenched case. We also evaluate the function. The criticality plane is drawn in the ð; N f Þ phase space which clearly depicts how larger N f is required to restore chiral symmetry for an increasing interaction strength.

We study chiral symmetry breaking for fundamental charged fermions coupled electromagnetically to photons with the inclusion of four-fermion contact self-interaction term, characterized by coupling strengths α and λ, respectively. We employ multiplicatively renormalizable models for the photon dressing function and the electron-photon vertex which minimally ensures mass anomalous dimension γm = 1. Vacuum polarization screens the interaction strength. Consequently, the pattern of dynamical mass generation for fermions is characterized by a critical number of massless fermion flavors N f = N c f above which chiral symmetry is restored. This effect is in diametrical opposition to the existence of criticality for the minimum interaction strengths, αc and λc, necessary to break chiral symmetry dynamically. The presence of virtual fermions dictates the nature of phase transition. Miransky scaling laws for the electromagnetic interaction strength α and the four-fermion coupling λ, observed for quenched QED, are replaced by a mean-field power law behavior corresponding to a second order phase transition. These results are derived analytically by employing the bifurcation analysis, and are later confirmed numerically by solving the original non-linearized gap equation. A three dimensional critical surface is drawn in the phase space of (α, λ, N f ) to clearly depict the interplay of their relative strengths to separate the two phases. We also compute the β-functions (βα and β λ ), and observe that αc and λc are their respective ultraviolet fixed points. The power law part of the momentum dependence, describing the mass function, implies γm = 1 + s, which reproduces the quenched limit trivially. We also comment on the continuum limit and the triviality of QED. 11.30.Rd, 11.15.Tk Since the works of Maskawa and Nakajima as well as the Kiev group [1], it is well known that quenched quantum electrodynamics (QED) exhibits vacuum rearrangement, which triggers chiral symmetry breaking when the interaction strength α = e 2 /(4π) exceeds a critical value α c ∼ 1. α c was argued to be an ultraviolet stable fixed point defining the continuum limit in supercritical QED. Although these works were carried out for the bare vertex in the Landau gauge, principle qualitative conclusions were later shown to be robust even for the most general and sophisticated ansätze put forward henceforth for an arbitrary value of the covariant gauge parameter, see e.g., [2][3][4][5]. Bardeen, Leung and Love [6] demonstrated that the composite operatorψψ acquires large anomalous dimensions at α = α c . In fact, the mass anomalous dimension was shown to be γ m = 1, leading to the fact that the four-fermion interaction operator (ψψ) 2 acquires the scaling dimension of d = 2(3 − γ m ) = 4 instead of 6, and becomes renormalizable. This is an example of when an interaction which is irrelevant in a certain region of phase space (perturbative) might become relevant in another (non perturbative). Consequently, the four-fermion contact interaction becomes mar...