8,325 research outputs found
Minimal Flavor Constraints for Technicolor
We analyze the constraints on the the vacuum polarization of the standard
model gauge bosons from a minimal set of flavor observables valid for a general
class of models of dynamical electroweak symmetry breaking. We will show that
the constraints have a strong impact on the self-coupling and masses of the
lightest spin-one resonances. Our analysis is applicable to any four and higher
dimensional extension of the standard model reducing to models of dynamical
electroweak symmetry breaking.Comment: 26 pages, we have added appendix C and some references and corrected
some typo
Giant Optical Non-linearity induced by a Single Two-Level System interacting with a Cavity in the Purcell Regime
A two-level system that is coupled to a high-finesse cavity in the Purcell
regime exhibits a giant optical non-linearity due to the saturation of the
two-level system at very low intensities, of the order of one photon per
lifetime. We perform a detailed analysis of this effect, taking into account
the most important practical imperfections. Our conclusion is that an
experimental demonstration of the giant non-linearity should be feasible using
semiconductor micropillar cavities containing a single quantum dot in resonance
with the cavity mode.Comment: 40 pages, 16 figures, accepted in Phys. Rev.
CO and HI observations of an enigmatic cloud
An isolated HI cloud with peculiar properties has recently been discovered by
Dedes, Dedes, & Kalberla (2008, A&A, 491, L45) with the 300-m Arecibo
telescope, and subsequently imaged with the VLA. It has an angular size of ~6',
and the HI emission has a narrow line profile of width ~ 3 km/s.
We explore the possibility that this cloud could be associated with a
circumstellar envelope ejected by an evolved star.
Observations were made in the rotational lines of CO with the IRAM-30m
telescope, on three positions in the cloud, and a total-power mapping in the HI
line was obtained with the Nancay Radio Telescope.
CO was not detected and seems too underabundant in this cloud to be a
classical late-type star circumstellar envelope. On the other hand, the HI
emission is compatible with the detached-shell model that we developed for
representing the external environments of AGB stars.
We propose that this cloud could be a fossil circumstellar shell left over
from a system that is now in a post-planetary-nebula phase. Nevertheless, we
cannot rule out that it is a Galactic cloud or a member of the Local Group,
although the narrow line profile would be atypical in both cases.Comment: Accepted for publication in Astronomy and Astrophysic
Circumstellar HI and CO around the carbon stars V1942 Sgr and V CrB
Context. The majority of stars that leave the main sequence are undergoing
extensive mass loss, in particular during the asymptotic giant branch (AGB)
phase of evolution. Observations show that the rate at which this phenomenon
develops differs highly from source to source, so that the time-integrated mass
loss as a function of the initial conditions (mass, metallicity, etc.) and of
the stage of evolution is presently not well understood. Aims. We are
investigating the mass loss history of AGB stars by observing the molecular and
atomic emissions of their circumstellar envelopes. Methods. In this work we
have selected two stars that are on the thermally pulsing phase of the AGB
(TP-AGB) and for which high quality data in the CO rotation lines and in the
atomic hydrogen line at 21 cm could be obained. Results. V1942 Sgr, a carbon
star of the Irregular variability type, shows a complex CO line profile that
may originate from a long-lived wind at a rate of ~ 10^-7 Msol/yr, and from a
young (< 10^4 years) fast outflow at a rate of ~ 5 10^-7 Msol/yr. Intense HI
emission indicates a detached shell with 0.044 Msol of hydrogen. This shell
probably results from the slowing-down, by surrounding matter, of the same
long-lived wind observed in CO that has been active during ~ 6 10^5 years. On
the other hand, the carbon Mira V CrB is presently undergoing mass loss at a
rate of 2 10^-7 Msol/yr, but was not detected in HI. The wind is mostly
molecular, and was active for at most 3 10^4 years, with an integrated mass
loss of at most 6.5 10^-3 Msol. Conclusions. Although both sources are carbon
stars on the TP-AGB, they appear to develop mass loss under very different
conditions, and a high rate of mass loss may not imply a high integrated mass
loss.Comment: Accepted for publication in Astron. Astrophy
Dynamical ultrafast all-optical switching of planar GaAs/AlAs photonic microcavities
The authors study the ultrafast switching-on and -off of planar GaAs/AlAs
microcavities. Up to 0.8% refractive index changes are achieved by optically
exciting free carriers at 1720 nm and a pulse energy of 1.8 micro Joules. The
cavity resonance is dynamically tracked by measuring reflectivity versus time
delay with tunable laser pulses, and is found to shift by as much as 3.3
linewidths within a few picoseconds. The switching-off occurs with a decay time
of around 50 ps. The authors derive the dynamic behavior of the carrier density
and of the complex refractive index. They propose that the inferred 10 GHz
switching rate may be tenfold improved by optimized sample growth.Comment: 1.) Replaced figure 1 (linear reflectivity) with a more recent and
improved measurement 2.) Included a Figure of Merit for switching and
compared to other recent contributions 3.) Explained more precisely the
effect of embedded Quantum Dots (namely no effect on measurement) 4.) Changed
wording in a few place
Microwave Lens for Polar Molecules
We here report on the implementation of a microwave lens for neutral polar
molecules suitable to focus molecules both in low-field-seeking and in
high-field-seeking states. By using the TE_11m modes of a 12 cm long
cylindrically symmetric microwave resonator, Stark-decelerated ammonia
molecules are transversally confined. We investigate the focusing properties of
this microwave lens as a function of the molecules' velocity, the detuning of
the microwave frequency from the molecular resonance frequency, and the
microwave power. Such a microwave lens can be seen as a first important step
towards further microwave devices, such as decelerators and traps.Comment: 4 pages, 3 figure
The Fluctuating Intergalactic Radiation Field at Redshifts z = 2.3-2.9 from He II and H I Absorption towards HE 2347-4342
We provide an in-depth analysis of the He II and H I absorption in the
intergalactic medium (IGM) at redshifts z = 2.3-2.9 toward HE 2347-4342, using
spectra from the Far Ultraviolet Spectroscopic Explorer (FUSE) and the
Ultraviolet-Visual Echelle Spectrograph (UVES) on the VLT telescope. Following
up on our earlier study (Kriss et al. 2001, Science, 293, 1112), we focus here
on two major topics: (1) small-scale variability (Delta z = 10^-3) in the ratio
eta = N(He II)/N(H I); and (2) an observed correlation of high-eta absorbers
(soft radiation fields) with voids in the (H I) Ly-alpha distribution. These
effects may reflect fluctuations in the ionizing sources on scales of 1 Mpc,
together with radiative transfer through a filamentary IGM whose opacity
variations control the penetration of 1-5 ryd radiation over 30-40 Mpc
distances. Owing to photon statistics and backgrounds, we can measure optical
depths over the ranges 0.1 < tau(HeII) < 2.3 and 0.02 < tau(HI) < 3.9, and
reliably determine values of eta = 4 tau(HeII)/tau(HI) over the range 0.1 to
460. Values of eta = 20-200 are consistent with models of photoionization by
quasars with observed spectral indices alpha_s = 0-3. Values of eta > 200 may
require additional contributions from starburst galaxies, heavily filtered
quasar radiation, or density variations. Regions with eta < 30 may indicate the
presence of local hard sources. We find that eta is higher in "void" regions,
where H I is weak or undetected and 80% of the path length has eta > 100. These
voids may be ionized by soft sources (dwarf starbursts) or by QSO radiation
softened by escape from the AGN cores or transfer through the "cosmic web". The
apparent differences in ionizing spectra may help to explain the 1.45 Gyr lag
between the reionization epochs, z(HI) = 6.2 +/-0.2 and z(HeII) = 2.8 +/-0.2.Comment: 27 pages, 7 figures, to appear in Ap
Spin Needlets for Cosmic Microwave Background Polarization Data Analysis
Scalar wavelets have been used extensively in the analysis of Cosmic
Microwave Background (CMB) temperature maps. Spin needlets are a new form of
(spin) wavelets which were introduced in the mathematical literature by Geller
and Marinucci (2008) as a tool for the analysis of spin random fields. Here we
adopt the spin needlet approach for the analysis of CMB polarization
measurements. The outcome of experiments measuring the polarization of the CMB
are maps of the Stokes Q and U parameters which are spin 2 quantities. Here we
discuss how to transform these spin 2 maps into spin 2 needlet coefficients and
outline briefly how these coefficients can be used in the analysis of CMB
polarization data. We review the most important properties of spin needlets,
such as localization in pixel and harmonic space and asymptotic uncorrelation.
We discuss several statistical applications, including the relation of angular
power spectra to the needlet coefficients, testing for non-Gaussianity on
polarization data, and reconstruction of the E and B scalar maps.Comment: Accepted for publication in Phys. Rev.
The Dynamics of a Strongly Driven Two Component Bose-Einstein Condensate
We consider a two component Bose-Einstein condensate in two spatially localized modes of a double well potential, with periodic modulation of the tunnel coupling between the two modes. We treat the driven quantum field using a two mode expansion and define the quantum dynamics in terms of the Floquet Operator for the time periodic Hamiltonian of the system. It has been shown that the corresponding semiclassical mean-field dynamics can exhibit regions of regular and chaotic motion. We show here that the quantum dynamics can exhibit dynamical tunneling between regions of regular motion, centered on fixed points (resonances) of the semiclassical dynamics
Place Bonding and Trust: The Case of Feral Hog Management Surrounding Big Thicket National Preserve
The management of feral hogs surrounding the Big Thicket National Preserve (BTNP) in Texas calls for managers and stakeholders to work together to manage resource issues. Research has indicated that place bonding can be a common ground upon which managers and stakeholders develop trust in one another to form a basis for collaborative management. However, such research has not examined the different types of trust (e.g., trust in local managers and trust in an entire agency) that exist. This investigation compared several models of trust and then sought to identify the relationship between place bonding and trust. Data were collected through a mail survey of residents living near the BTNP. The results suggested that a conceptualization of trust wherein an individual’s institutional trust in an agency contributes to their social trust in agency managers explained the most variance. The analysis also confirmed a place bonding—trust relationship
- …