71 research outputs found
Dirac Magnetic Monopole Production from Photon Fusion in Proton Collisions
We calculate the lowest order cross--section for Dirac magnetic monopole
production from photon fusion in p p-bar collisions at sqrt{s}=1.96 TeV, p p
collisions at sqrt{s}=14 TeV, and we compare photon fusion with Drell--Yan (DY)
production. We find the total photon fusion cross--section is comparable with
DY at sqrt{s}=1.96 TeV and dominates DY by a factor ~50 at sqrt{s}=14 TeV. We
conclude that both the photon fusion and DY processes allow for a monopole mass
limit m>370 GeV based upon the null results of the recent monopole search at
the Collider Detector at Fermilab (CDF). We also conclude that photon fusion is
the leading production mechanism to be considered for direct monopole searches
at the Large Hadron Collider (LHC).Comment: 9 pages, 4 figures, minor correction, one reference adde
Signature Studies of Cosmic Magnetic Monopoles
This talk explores the possibility that the Universe may be populated with
relic magnetic monopoles. Observations of galactic and extragalactic magnetic
fields, lead to the conclusion that monopoles of mass < 10^{14} GeV are
accelerated in these fields to relativistic velocities. The relativistic
monopole signatures and features we derive are (i) the protracted shower
development, (ii) the Cherenkov signals, (iii) the tomography of the Earth with
monopoles, and (iv) a model for monopole airshowers above the GZK cutoff.Comment: 10 pages, 2 figures, talk given at the First International Workshop
on Radio Detection of High--Energy Particles, November 16 - 18, 2000, UCL
High-Energy Cosmic Rays from Gamma-Ray Bursts
A model is proposed for the origin of cosmic rays (CRs) from ~10^14 eV to the
highest energies, >10^20 eV. Gamma-Ray Bursts (GRBs) are assumed to inject CR
protons and ions into the interstellar medium of star-forming
galaxies--including the Milky Way--with a power law spectrum extending to a
maximum energy ~10^20 eV. The CR spectrum near the knee is fit with CRs trapped
in the Galactic halo that were accelerated and injected by an earlier Galactic
GRB. These CRs diffuse in the disk and halo of the Galaxy due to gyroresonant
pitch-angle scattering with MHD turbulence in the Galaxy's magnetic field. The
preliminary (2001) KASCADE data through the knee of the CR spectrum are fit by
a model with energy-dependent propagation of CR ions from a single Galactic
GRB. Ultra-high energy CRs (UHECRs), with energies above the ankle are assumed
to propagate rectilinearly with their spectrum modified by photo-pion,
photo-pair, and expansion losses. We fit the measured UHECR spectrum assuming
comoving luminosity densities of GRB sources consitent with possible star
formation rate histories of the universe. For power-law CR proton injection p>2
this model implies that the nonthermal content in the GRB blast waves is
hadronically dominated by a factor ~60-200. Calculations show that 100 TeV-100
PeV neutrinos could be detected several times per year from all GRBs in
kilometer-scale neutrino detectors such as IceCube, for GRB blast-wave Doppler
factors <~200. GLAST measurements of gamma-ray components and cutoffs will
constrain the product of nonthermal baryon loading and radiative efficiency,
limit the Doppler factor, and test this senario.Comment: 43 pages, 21 figures, to appear in Astropart. Phy
Solar Wakes of Dark Matter Flows
We analyze the effect of the Sun's gravitational field on a flow of cold dark
matter (CDM) through the solar system in the limit where the velocity
dispersion of the flow vanishes. The exact density and velocity distributions
are derived in the case where the Sun is a point mass. The results are extended
to the more realistic case where the Sun has a finite size spherically
symmetric mass distribution. We find that regions of infinite density, called
caustics, appear. One such region is a line caustic on the axis of symmetry,
downstream from the Sun, where the flow trajectories cross. Another is a
cone-shaped caustic surface near the trajectories of maximum scattering angle.
The trajectories forming the conical caustic pass through the Sun's interior
and probe the solar mass distribution, raising the possibility that the solar
mass distribution may some day be measured by a dark matter detector on Earth.
We generalize our results to the case of flows with continuous velocity
distributions, such as that predicted by the isothermal model of the Milky Way
halo.Comment: 30 pages, 8 figure
Neurogenesis Drives Stimulus Decorrelation in a Model of the Olfactory Bulb
The reshaping and decorrelation of similar activity patterns by neuronal
networks can enhance their discriminability, storage, and retrieval. How can
such networks learn to decorrelate new complex patterns, as they arise in the
olfactory system? Using a computational network model for the dominant neural
populations of the olfactory bulb we show that fundamental aspects of the adult
neurogenesis observed in the olfactory bulb -- the persistent addition of new
inhibitory granule cells to the network, their activity-dependent survival, and
the reciprocal character of their synapses with the principal mitral cells --
are sufficient to restructure the network and to alter its encoding of odor
stimuli adaptively so as to reduce the correlations between the bulbar
representations of similar stimuli. The decorrelation is quite robust with
respect to various types of perturbations of the reciprocity. The model
parsimoniously captures the experimentally observed role of neurogenesis in
perceptual learning and the enhanced response of young granule cells to novel
stimuli. Moreover, it makes specific predictions for the type of odor
enrichment that should be effective in enhancing the ability of animals to
discriminate similar odor mixtures
Signatures for a Cosmic Flux of Magnetic Monopoles
Any early universe phase transition occurring after inflation has the
potential to populate the universe with relic magnetic monopoles. Observations
of galactic magnetic fields, as well as observations matched with models for
extragalactic magnetic fields, lead to the conclusion that monopoles of mass
\lsim 10^{15} GeV are accelerated in these fields to relativistic velocities.
We explore the possible signatures of a cosmic flux of relativistic monopoles
impinging on the earth. The electromagnetically-induced signatures of monopoles
are reliable. The hadronically-induced signatures are highly model-dependent.
Among our findings are (i) the electromagnetic energy losses of monopoles
continuously initiate a protracted shower of small intensity; (ii) monopoles
may traverse the earth's diameter, making them a probe of the earth's interior
structure; (iii) in addition to the direct monopole Cherenkov signal presently
employed, a very attractive search strategy for monopoles is detection of their
radio-Cherenkov signal produced by the coherent charge-excess in the
shower - in fact, Cherenkov-detectors have the potential to discover a monopole
flux (or limit it) several orders of magnitude below the theoretical Parker
limit of /s/sr; (iv) it is conceivable (but not compelling)
that bound states of colored monopoles may be the primary particles initiating
the air showers observed above the GZK cutoff.Comment: 33 pages, 5 figures, revtex, to appear in Astro. Part. Phy
Effect of Neutralizing Monoclonal Antibody Treatment on Early Trajectories of Virologic and Immunologic Biomarkers in Patients Hospitalized With COVID-19
BACKGROUND: Neutralizing monoclonal antibodies (nmAbs) failed to show clear benefit for hospitalized patients with coronavirus disease 2019 (COVID-19). Dynamics of virologic and immunologic biomarkers remain poorly understood.
METHODS: Participants enrolled in the Therapeutics for Inpatients with COVID-19 trials were randomized to nmAb versus placebo. Longitudinal differences between treatment and placebo groups in levels of plasma nucleocapsid antigen (N-Ag), anti-nucleocapsid antibody, C-reactive protein, interleukin-6, and D-dimer at enrollment, day 1, 3, and 5 were estimated using linear mixed models. A 7-point pulmonary ordinal scale assessed at day 5 was compared using proportional odds models.
RESULTS: Analysis included 2149 participants enrolled between August 2020 and September 2021. Treatment resulted in 20% lower levels of plasma N-Ag compared with placebo (95% confidence interval, 12%-27%; P \u3c .001), and a steeper rate of decline through the first 5 days (P \u3c .001). The treatment difference did not vary between subgroups, and no difference was observed in trajectories of other biomarkers or the day 5 pulmonary ordinal scale.
CONCLUSIONS: Our study suggests that nmAb has an antiviral effect assessed by plasma N-Ag among hospitalized patients with COVID-19, with no blunting of the endogenous anti-nucleocapsid antibody response. No effect on systemic inflammation or day 5 clinical status was observed.
CLINICAL TRIALS REGISTRATION: NCT04501978
Expanding Stereochemical and Skeletal Diversity Using Petasis Reactions and 1,3-Dipolar Cycloadditions
A short and modular synthetic pathway using intramolecular 1,3-dipolar cycloaddition reactions and yielding functionalized isoxazoles, isoxazolines, and isoxazolidines is described. The change in shape of previous compounds and those in this study is quantified and compared using principal moment-of-inertia shape analysis.Chemistry and Chemical Biolog
GUT Cosmic Magnetic Fields in a Warm Inflationary Universe
Sources of magnetic fields from grand unified theories are studied in the
warm inflation regime. A ferromagnetic Savvidy vacuum scenario is presented
that yields observationally interesting large scale magnetic fields. As an
intermediate step, a general analysis is made of defect production at the onset
of warm inflation and monopole constraints are obtained. Many features of this
Savvidy vacuum scenario are applicable within a supercooled inflation regime
and these points are discussed.Comment: 15 pages, Latex, In press Physical Review
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