2,101 research outputs found
Fringe spacing and phase of interfering matter waves
We experimentally investigate the outcoupling of atoms from Bose-Einstein
condensates using two radio-frequency (rf) fields in the presence of gravity.
We show that the fringe separation in the resulting interference pattern
derives entirely from the energy difference between the two rf fields and not
the gravitational potential difference. We subsequently demonstrate how the
phase and polarisation of the rf radiation directly control the phase of the
matter wave interference and provide a semi-classical interpretation of the
results.Comment: 4 pages, 3 figure
A necklace of Wulff shapes
In a probabilistic model of a film over a disordered substrate, Monte-Carlo
simulations show that the film hangs from peaks of the substrate. The film
profile is well approximated by a necklace of Wulff shapes. Such a necklace can
be obtained as the infimum of a collection of Wulff shapes resting on the
substrate. When the random substrate is given by iid heights with exponential
distribution, we prove estimates on the probability density of the resulting
peaks, at small density
Comparison of Strangeness Production between A+A and p+p Reactions from 2 to 160 AGeV
The measured K ratios from heavy-ion reactions are compared with
the K ratios from p+p reactions over the energy range 2-160 AGeV. The
K/ enhancement in heavy-ion reactions is largest at the lower energies,
consistent with strangeness production in secondary scattering becoming
relatively more important than initial collisions near the kaon production
threshold. The enhancement decreases steadily from 4 to 160 AGeV, suggesting
that the same enhancement mechanism of hadronic rescattering and decay of
strings may be applicable over this full energy range. Based on existing data,
the mid-rapidity K ratio is predicted to be for the
forthcoming Pb+Pb reactions at 40 AGeV/c.Comment: 14 pages, 4 figures, submitted to Phys. Rev.
The K/pi ratio from condensed Polyakov loops
We perform a field-theoretical computation of hadron production in large
systems at the QCD confinement phase transition associated with restoration of
the Z(3) global symmetry. This occurs from the decay of a condensate for the
Polyakov loop. From the effective potential for the Polyakov loop, its mass
just below the confinement temperature T_c is in between the vacuum masses of
the pion and that of the kaon. Therefore, due to phase-space restrictions the
number of produced kaons is roughly an order of magnitude smaller than that of
produced pions, in agreement with recent results from collisions of gold ions
at the BNL-RHIC. From its mass, we estimate that the Polyakov loop condensate
is characterized by a (spatial) correlation scale of 1/m_\ell ~ 1/2 fm. For
systems of deconfined matter of about that size, the free energy may not be
dominated by a condensate for the Polyakov loop, and so the process of
hadronization may be qualitatively different as compared to large systems. In
that vein, experimental data on hadron abundance ratios, for example K/pi, in
high-multiplicity pp events at high energies should be very interesting.Comment: 7 pages, 4 figures; discussion of the two-point function of Polyakov
Loops in small versus large systems adde
GZK Photons Above 10 EeV
We calculate the flux of "GZK-photons", namely the flux of photons produced
by extragalactic nucleons through the resonant photoproduction of pions, the so
called GZK effect. This flux depends on the UHECR spectrum on Earth, of the
spectrum of nucleons emitted at the sources, which we characterize by its slope
and maximum energy, on the distribution of sources and on the intervening
cosmological backgrounds, in particular the magnetic field and radio
backgrounds. For the first time we calculate the GZK photons produced by
nuclei. We calculate the possible range of the GZK photon fraction of the total
UHECR flux for the AGASA and the HiRes spectra. We find that for nucleons
produced at the sources it could be as large as a few % and as low as 10^{-4}
above 10 EeV. For nuclei produced at the sources the maximum photon fraction is
a factor of 2 to 3 times smaller above 10 EeV but the minimum could be much
smaller than for nucleons. We also comment on cosmogenic neutrino fluxes.Comment: 20 pages, 9 figures (21 panels), iopart.cls and iopart12.clo needed
to typese
The VIMOS Ultra Deep Survey: Ly Emission and Stellar Populations of Star-Forming Galaxies at 2<z<2.5
The aim of this paper is to investigate spectral and photometric properties
of 854 faint (<~25 mag) star-forming galaxies (SFGs) at 2<z<2.5 using
the VIMOS Ultra-Deep Survey (VUDS) spectroscopic data and deep multi-wavelength
photometric data in three extensively studied extragalactic fields (ECDFS,
VVDS, COSMOS). These SFGs were targeted for spectroscopy based on their
photometric redshifts. The VUDS spectra are used to measure the UV spectral
slopes () as well as Ly equivalent widths (EW). On average, the
spectroscopically measured (-1.360.02), is comparable to the
photometrically measured (-1.320.02), and has smaller measurement
uncertainties. The positive correlation of with the Spectral Energy
Distribution (SED)-based measurement of dust extinction, E(B-V),
emphasizes the importance of as an alternative dust indicator at high
redshifts. To make a proper comparison, we divide these SFGs into three
subgroups based on their rest-frame Ly EW: SFGs with no Ly
emission (SFG; EW0\AA), SFGs with Ly emission (SFG; EW0\AA), and Ly emitters (LAEs; EW20\AA). The fraction of
LAEs at these redshifts is 10%, which is consistent with previous
observations. We compared best-fit SED-estimated stellar parameters of the
SFG, SFG and LAE samples. For the luminosities probed here
(L), we find that galaxies with and without Ly in emission
have small but significant differences in their SED-based properties. We find
that LAEs have less dust, and lower star-formation rates (SFR) compared to
non-LAEs. We also find that LAEs are less massive compared to non-LAEs, though
the difference is smaller and less significant compared to the SFR and E(B-V). [abridged]Comment: Accepted for publication in A&A, 19 pages, 10 figures, 1 tabl
The evolution of clustering length, large-scale bias and host halo mass at 2<z<5 in the VIMOS Ultra Deep Survey (VUDS)
We investigate the evolution of galaxy clustering for galaxies in the
redshift range 2.0<<5.0 using the VIMOS Ultra Deep Survey (VUDS). We present
the projected (real-space) two-point correlation function measured
by using 3022 galaxies with robust spectroscopic redshifts in two independent
fields (COSMOS and VVDS-02h) covering in total 0.8 deg. We quantify how the
scale dependent clustering amplitude changes with redshift making use of
mock samples to evaluate and correct the survey selection function. Using a
power-law model we find that the correlation
function for the general population is best fit by a model with a clustering
length =3.95 hMpc and slope
=1.8 at ~2.5, =4.350.60 hMpc and
=1.6 at ~3.5. We use these clustering parameters
to derive the large-scale linear galaxy bias , between galaxies and
dark matter. We find = 2.680.22 at redshift ~3 (assuming
= 0.8), significantly higher than found at intermediate and low
redshifts. We fit an HOD model to the data and we obtain that the average halo
mass at redshift ~3 is =10 hM. From
this fit we confirm that the large-scale linear galaxy bias is relatively high
at = 2.820.27. Comparing these measurements with similar
measurements at lower redshifts we infer that the star-forming population of
galaxies at ~3 should evolve into the massive and bright (<-21.5)
galaxy population which typically occupy haloes of mass =
10 h at redshift =0.Comment: 19 pages, 10 figures, submitted to A&
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