We explore cosmological implications of dark matter as
massive particles trapped on a brane embedded in a large
Randall-Sundrum noncompact higher dimensional AdS_5 space.
It is a likely consequence of this cosmology that massive
particles are metastable and can disappear into the bulk
dimension. Here, we show that a massive dark matter particle
(e.g. the lightest supersymmetric particle) is likely to
have the shortest lifetime for disappearing into the bulk.
We examine cosmological constraints on this new paradigm and
show that disappearing dark matter is consistent (at the
95% confidence level) with all cosmological constraints,
i.e. present observations of Type Ia supernovae at the
highest redshift, trends in the mass-to-light ratios of
galaxy clusters with redshift, the fraction of X-ray
emitting gas in rich clusters, and the spectrum of power
fluctuations in the cosmic microwave background. A best
2-sigma concordance region is identified corresponding to a
mean lifetime for dark matter disappearance of 15 < t < 80
Gyr. The implication of these results for brane-world
physics is discussed.
[W10.002] A Chemical Evolution Explanation for the Apparent Time-Dependent Fine Structure Constant
Timothy Ashenfelter, Grant Mathews (Univ. Notre Dame), Keith Olive (Univ. Minn.)
The many-multiplet method applied to high redshift quasar
absorption spectra has been interpreted as evidence for a
possible time variation of the fine structure constant.
However, a constant value of \alpha can be made consistent
with the observational analysis if a non-solar isotopic
ratio of ^24,25,26Mg occurs at large (0.5 < z < 1.8)
redshifts . A higher abundance of the heavier isotopes
^25,26Mg are required to explain the observed multiplet
splitting. We show that new stellar evolution calculations
enhance the synthesis of ^25,26Mg at the base of the
convective envelope in low-metallicity asymptotic giant
branch stars. Furthermore, there is evidence for a burst of
intermediate-mass AGB stars at low metallicity. Hence, a
simple model of galactic chemical evolution can produce the
required isotopic ratios. This model is supported both by
recent observations of high abundances for neutron-rich Mg
isotopes in metal-poor globular-cluster stars and evidence
of an enhancement in the population of carbon-enriched stars
at low metallicity. We conclude that the present data based
on quasar absorption spectra may be providing interesting
information on the nucleosynthetic history of such systems
rather than a time variation of fundamental constants.
[W10.003] A Rejuvenated Universe Without Initial Singularity
Eric Gawiser (Yale University)
Cosmological observations show that dark energy dominates
the current energy density of the universe. The equation of
state relating the pressure and energy density of this dark
energy, p = w \rho, appears to have w \simeq -1, with most
analyses preferring w<-1. Dark energy with w<-1 causes the
universe to undergo superexponential expansion in which the
scale factor, expansion rate, and energy density of the
universe diverge in a finite time. I will present the recent
hypothesis (Gawiser 2003, astro-ph/0312440) that w>-1 is
restored due to a phase transition at high energy density
and show that this produces conditions observationally
indistinguishable from the Hot Big Bang. Hence the current
dark energy can serve as initial conditions for an apparent
Big Bang without a spacetime singularity. This process of
rejuvenation may have occurred in our past, making our
universe much older than it appears.
[W10.004] Do Relaxed Clusters of Galaxies Exist?
Patrick M. Motl, Jack O. Burns (University of Colorado - Boulder), Michael L. Norman (University of California, San Diego)
Clusters of galaxies lacking observational signatures of
mergers and other complications are popular targets as
cosmological probes. However, the assumptions of structural
simplicity must be approximations that are valid to only a
certain level. Especially in the new era of precision
cosmology where efforts are underway to investigate the
nature and evolution of dark energy, it is crucial to
calibrate the approximations used to reduce cluster
observations to cosmological measurements. We use
high-resolution simulations of clusters of galaxies, evolved
within their cosmological environment, to study the process
of reducing X-ray and/or Sunyaev-Zeldovich data to cluster
observables such as the gravitating mass and Hubble
constant. This allows us to measure the impact of structure
formation on these observables and quantify the
approximations used in interpreting cluster observations.
[W10.005] Wide-field weak lensing by RXJ1347-1145
Thomas P. Kling (Bridgewater State College), Ian Dell'Antonio (Brown Univesity), David Wittman, J Anthony Tyson (Bell-Labs Lucent Technologies)
We present an analysis of weak lensing observations for
RXJ1347--1145 over a 43\,' \, \times \, 43 \, ' field
taken in B and R filters on the Blanco 4m telescope at
CTIO. RXJ1347--1145 is a massive cluster at redshift
z=0.45. Using a population of galaxies with 20
We present the first measurement of the very high energy
(VHE, E>300 GeV) gamma-ray spectrum of the BL Lacertae
object 1ES 2344+514. At a redshift of 0.044, it is one of
five active galactic nuclei (AGN) detected by the Whipple
collaboration. As is typical for these high frequency peaked
blazars, the VHE gamma-ray emission is highly variable. On
the night of 20 Dec. 1995, a gamma-ray flare of 5.3-sigma
significance was detected (Catanese et al., ApJ, 1998, 501,
p616). 1ES2344+514 then remained below detection threshold
for over a year, but was detected again by Whipple in the
1999-2001 observing seasons (Badran et al., Proc. Gamma
2001, AIP, 587, p281). Recently, the HEGRA collaboration
reported an independent confirmation of this source
(Tluczykont et al., ICRC 2003, 5, p2547). The implication of
this measurement on the extragalactic infrared background
will be discussed.
We report on observations of Markarian 421 made with the
Whipple 10m Cerenkov telescope and the RXTE satellite during
a multi-wavelength campaign in December 2002 and January
2003, initiated by the detection of a flaring state by the
Whipple 10m telescope and the Rossi X-ray Timing Explorer
All Sky Monitor (RXTE ASM). The observations revealed
several flares with flux levels between 1 and 1.5 times the
flux of the Crab Nebula. We will present results of the
mutli-wavelength campaign, which included observations in
the optical (courtesy of Paul Boltwood and LaPalma), radio
(coursety of the University of Michigan Radio Astronomy
Observeratory, x-ray (taken with the RXTE PCA and ASM), and
TeV gamma-ray bands (taken with the Whipple 10m telescope,
as well as the HEGRA CT1 telescope). The observations
covered several flares of intermediate strength. We will
discuss the temporal properties, including evidence of
X-ray/TeV gamma-ray flux correlation.
In plasma accretion disks from which jets can emerge it is
reasonable to consider physical regimes where the magnetic
field energy can be of the order of the thermal energy. The
axisymmetric magnetic and electric field configurations that
can be present in thin disks, in these regimes, is
discussed. Two-dimensional modes, that can be excited from
axisymmetric equilibrium disk configurations have to be of
the ballooning kind [1]in the vertical direction and have an
intrinsic difficulty in fitting into the height of the disk
[2]. Conversely, bending (tridimensional)modes that are
singular when described by the linearized ideal MHD
approximation can be excited and lead to significant rates
of outward transport of the angular momentum allowing for
the occurrence of accretion. However, these modes and their
growth rates depend on the nonlinear processes that make the
transition across the ideal MHD singularities possible. A
broad class of non linear equations that can be suitable for
this are identified. The considered modes are localized
around the radius where they co-rotate with the disk and the
singularities correspond to the radii where the relevant
Doppler shifted frequency becomes equal to the slow
magnetosonic frequency and to the shear Alfvén wave
frequency[1].
*Sponsored in part by the U.S. D.O.E.
[1] B. Coppi and P.S. Coppi, Phys. Rev. Letters 85, 5,
051101-1 (2001)
[2] B. Coppi and E.A. Keyes, Ap. J. \bf595, 1000 (2003).
Extragalactic jets are created in accretion disks around
supermassive black holes and retain their collimation for
distances as far as the order of the megaparsec.
Understanding the physical causes of this remarkable, and
ill-understood collimation over such large distances is a
great challenge. Many authors have attempted to understand
the processes in terms of MHD equilibria, based on the
analysis on the Grad-Shafranov (GS) equation. Recently, we
have proposed a new approach in this direction of
investigation [1]. Based on a mathematical analogy between
the GS equation and the non-linear Schrodinger equation for
solitons, we have proposed a class of solutions that are
mathematically similar to optical solitons. In the present
work we show the results of a simulation study of the
stability of the soliton solutions conducted using the MHD
code FLIP. Using the specific example of the jet observed
from the active galactic nucleus (AGN) in the radio galaxy
3C303, we investigate the ability of the proposed model to
explain the observational evidence.
[1] G. Lapenta, Phys. Rev. Lett., 90, 135005, 2003.
The collapse of a molecular cloud to form a planetary system
is a classic process in astrophysics. The length scale of
the collapsed system and the rate of its formation is
described in the simplest model by the Jeans instability.
When the model is complicated by additional processes, the
rate and scale of the Jeans instability is modified [1]. We
focus on the processes involved with the charging of the
dust in the initial cloud. The presence of charge of the
same sign on the dust particles inhibits the process of
collapse. Yet, the process of charging is expected to be
operational. We propose a mechanism that can explain this
apparent contradiction. In a recent work [2], we have shown
that in presence of electron emission from the dust the
interaction potential of a dust particle becomes similar to
the Lennard-Jones (LJ) potential. The important consequence
of this discovery is that emitting dust particles with LJ
like potential can actually attract each other even though
they all share the same sign of charge. Here, we present a
series of simulations conducted with a new code designed to
study a large system of weakly coupled dust particles,
interacting with a LJ like potential.
[1] P. K. Shukla, Dust plasma interaction in space, Nova
Science Publ., 2002. [2] G.L. Delzanno, G. Lapenta, M.
Rosenberg, Phys. Rev. Lett., to appear.
We analyse the dynamical behaviour of eccentric orbits in a
triaxial logarithmic potential through an approximate map of
consecutive apocentres. Its vector angular momentum and the
unit vector of its apocentre define this map. The map is
generated using the fact that the torque is strongest at the
apocentre of the orbits. The evolution of the dynamic
variables between each consecutive map is obtained
approximating the non spherical terms in the gravitational
potential. This method it is better adapted for eccentric
orbits. This map yields the possibility to study the
characteristic of a large number of orbits in less time than
the traditional methods. Touma amp; Tremaine (1997)
introduced this map of consecutive apocentres, and used it
for the study of the case of a logarithmic potential of two
dimensions. Through the extension of this map to a triaxial
logarithmic potential, we are able to describe the
characteristics of many family of orbits. For some of those
orbits presenting a chaotic behaviour we have estimated the
Liapunov exponent.
As opposed to the situation in slow-roll cosmologies
(inflation), leading order quantum metric fluctuations about
deSitter are sourced by nonlinear quantum matter
fluctuations. We show how these quantum fluctuations are
forced to satisfy additional, nonlinear global constraints
which effectively impose SO(4,1) invariance on all of the
quantum states (i.e. not just the vacuum). We discuss how
these restrictions may relate to nonlinear quantum
corrections to the usual slow-roll inflation models.
[W10.006] VHE Gamma-Ray Spectrum of 1ES 2344+514
Martin Schroedter (Smithsonian Astrophysical Observatory / U. of Arizona), VERITAS Collaboration
[W10.007] Intensive TeV Gamma-Ray and X-Ray Observations of the Blazar Mrk 421 in December 2002 and January 2003
Paul Rebillot, Scott Hughes (Washington University, St. Louis, Department of Physics), Margo Aller, Hugh Aller (University of Michigan, Department of Astronomy), Paul Boltwood (1655 Main St, Stittsville, Ontario Canada), Daniel Kranich (University of California, Davis, Department of Physics), Alberto Sadun (University of Denver), Aimo Sillanpaa (University of Turku, Väisälä Institute for Space Physics and Astronomy), The VERITAS Collaboration
[W10.008] Physics of Plasma Accretion Disks
P. S. Coppi (Yale Univ.), B. Coppi (MIT)
[W10.009] A comparison of observations and simulations for the extragalactic jet from the AGN in 3C303
P. Kronberg, Giovanni Lapenta (LANL)
[W10.010] Jeans Collapse of a System of Electron Emitting Dust Particles
G.L. Delzanno (Burning Plasma Research Group), G. Lapenta (LANL)
[W10.011] Mapping for Eccentric Orbits in Triaxial Logarithmic Potential
Nelson Zamorano, Alfredo Gomez, Andres Meza (University of Chile)
[W10.012] Backreactions in deSitter and inflation
Bojan Losic (University of British Columbia)