MRI and clinical resolution of a suspected intracranial toxoplasma granuloma with medical treatment in a domestic short hair cat

A two-year-old cat was presented with a left paradoxical vestibular syndrome. MRI of the brain revealed an extra-axial homogenously contrast enhancing mass in the region of the left caudal cerebellar peduncle. Toxoplasma serology was consistent with active infection and the lesion was suspected to be a toxoplasma granuloma. Following eight weeks of tapering oral prednisolone and 11 weeks of oral clindamycin treatment, repeat MRI revealed resolution of the lesion. Eighteen months after initial diagnosis, the cat remained neurologically normal. Differential diagnoses for a solitary, extra-axial, contrast enhancing mass lesion in the feline brain should include toxoplasma granuloma, which can undergo MRI and clinical resolution with medical treatment

Probing MeV Dark Matter at Low--Energy e+e−e^+e^- Colliders

It has been suggested that the annihilation of Dark Matter particles \chi with mass between 0.5 and 20 MeV into e^+e^- pairs could be responsible for the excess flux of 511 keV photons coming from the central region of our galaxy that has been detected by the IINTEGRAL satellite. The simplest way to achieve the required cross section for \chi pair annihilation while respecting existing constraints is to introduce a new vector boson U with mass M_U below a few hundred MeV. In this Letter we point out that over most of the allowed parameter space, the process e^+e^- to U \gamma, followed by the decay of U into either an e^+e^- pair or into an invisible (\nu \bar \nu or \chi \bar \chi) channel, should lead to signals that can be detected by the B-factory experiments BaBar and Belle. A smaller, but still substantial, region of parameter space can also be probed at the \Phi factory DAFNE.Comment: 4 pages, revtex with equation.sty (included), 2 embedded postscript figures. Minor changes, added a couple of references; version to appear in PR

The Thermal Abundance of Semi-Relativistic Relics

Approximate analytical solutions of the Boltzmann equation for particles that are either extremely relativistic or non-relativistic when they decouple from the thermal bath are well established. However, no analytical formula for the relic density of particles that are semi-relativistic at decoupling is yet known. We propose a new ansatz for the thermal average of the annihilation cross sections for such particles, and find a semi-analytical treatment for calculating their relic densities. As examples, we consider Majorana- and Dirac-type neutrinos. We show that such semi-relativistic relics cannot be good cold Dark Matter candidates. However, late decays of meta-stable semi-relativistic relics might have released a large amount of entropy, thereby diluting the density of other, unwanted relics.Comment: 22 pages, 5 figures. Comments and references adde

Abundance of Cosmological Relics in Low-Temperature Scenarios

We investigate the relic density n_\chi of non-relativistic long-lived or stable particles \chi in cosmological scenarios in which the temperature T is too low for \chi to achieve full chemical equilibrium. The case with a heavier particle decaying into \chi is also investigated. We derive approximate solutions for n_\chi(T) which accurately reproduce numerical results when full thermal equilibrium is not achieved. If full equilibrium is reached, our ansatz no longer reproduces the correct temperature dependence of the \chi number density. However, it does give the correct final relic density, to an accuracy of about 3% or better, for all cross sections and initial temperatures.Comment: 26 pages, 8 figures, comments added, to appear in Phys. Rev.

Higgs funnel region of SUSY dark matter for small tan⁡β\tan\beta and renormalization group effects on pseudoscalar Higgs boson with scalar mass non-universality

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.Comment: 36 pages and 7 Postscript files. Minor changes in the text. Version accepted for publication in Phys. Rev.

A Simple Way of Calculating Cosmological Relic Density

A simple procedure is presented which leads to a dramatic simplification in the calculation of the relic density of stable particles in the Universe.Comment: 7 pages in LaTex, no figures; University of Michigan preprint UM-TH-94-02 (February 1994). Changes: a coefficient in $b^0$ (Eq. 16) corrected; added Acknowledgements and revised Note Added; plain LaTex only (no need to use RevTex

Rapidity Gap Events in Squark Pair Production at the LHC

The exchange of electroweak gauginos in the $t-$ or $u-$channel allows squark pair production at hadron colliders without color exchange between the squarks. This can give rise to events where little or no energy is deposited in the detector between the squark decay products. We discuss the potential for detection of such rapidity gap events at the Large Hadron Collider (LHC). Our numerical analysis is divided into two parts. First, we evaluate in a simplified framework the rapidity gap signal at the parton level. The second part covers an analysis with full event simulation using PYTHIA as well as Herwig++, but without detector simulation. We analyze the transverse energy deposited between the jets from squark decay, as well as the probability of finding a third jet in between the two hardest jets. For the mSUGRA benchmark point SPS1a we find statistically significant evidence for a color singlet exchange contribution. The systematical differences between current versions of PYTHIA and HERWIG++ are larger than the physical effect from color singlet exchange; however, these systematic differences could be reduced by tuning both Monte Carlo generators on normal QCD di--jet data.Comment: 23 pages, 10 figure

Virtual Photon Strucutre Functions and the Parton Content of the Electron

We point out that in processes involving the parton content of the photon the usual effective photon approximation should be modified. The reason is that the parton content of virtual photons is logarithmically suppressed compared to real photons. We describe this suppression using several simple, physically motivated ans\"atze. Although the parton content of the electron in general no longer factorizes into an electron flux function and a photon structure function, it can still be expressed as a single integral. Numerical examples are given for the \eplem\ collider TRISTAN as well as the $ep$ collider HERA.Comment: 16 pages and 3 figures (available from DREES@WSICPHEN as topdraw or PS files); LaTeX with equation.sty; MAD/PH/819, BU 94-0

Loop induced Higgs and Z boson couplings to Neutralinos and implications for collider and Dark Matter searches

We calculate the one-loop induced couplings of two gaugino-like neutralinos to the $Z$ and Higgs bosons in the Minimal Supersymmetric Standard Model. These couplings, which vanish at the tree level, can be generated through loops involving fermions and sfermions. We show that, while the neutralino contribution to the invisible $Z$ boson decay width remains small, the loop induced couplings to the lightest Higgs boson might be sufficiently large to yield a rate of invisible decays of this Higgs boson that should be detectable at future $e^+e^-$ colliders. We also study the implications of these couplings for direct searches of Dark Matter and show that they can modify appreciably the neutralino-nucleon elastic cross section for some parameter range.Comment: LaTeX with 6 (e)ps and 2 axodraw figures, 25 pages in total; axodraw.sty is included v.2: Added one figure and some discussions; version to appear in PR