Faculty
Publications added in June, 2008
Query
Results from the Smithsonian/NASA
Astrophysics Data System (ADS)
The
following are Harvard Physics faculty members' publications,
added to the ADS database last month. Please note that
some publications which apeared in print last month may
not be included in the database (and therefore may not
appear on this list) until the following month.
| Title: |
Large Synoptic Survey
Telescope: From Science Drivers To Reference
Design |
| Authors: |
Ivezic, Z.; Axelrod, T.; Brandt, W. N.; Burke, D. L.; Claver, C. F.; Connolly, A.; Cook, K. H.; Gee, P.; Gilmore, D. K.; Jacoby, S. H.; Jones, R. L.; Kahn, S. M.; Kantor, J. P.; v. Krabbendam, V.; Lupton, R. H.; Monet, D. G.; Pinto, P. A.; Saha, A.; Schalk, T. L.; Schneider, D. P.; Strauss, M. A.; Stubbs, C. W.; Sweeney, D.; Szalay, A.; Thaler, J. J.; Tyson, J. A. |
| Publication: |
Serbian Astronomical
Journal, vol. 176, p. 1-13 (SerAJ
Homepage) |
| Publication
Date: |
06/2008 |
| Origin: |
SerAJ |
| Keywords: |
Astronomical data
bases: miscellaneous, Atlases, Catalogs, Surveys,
Solar system: general, Stars: general, Galaxy:
general, Galaxies: general, Cosmology: miscellaneous |
| Abstract
Copyright: |
Astronomical Observatory
and Department of Astronomy, Belgrade |
| DOI: |
10.2298/SAJ0876001I |
| Bibliographic
Code: |
2008SerAJ.176....1I |
Abstract:
In the history of astronomy, major advances in our understanding
of the Universe have come from dramatic improvements
in our ability to accurately measure astronomical quantities.
Aided by rapid progress in information technology, current
sky surveys are changing the way we view and study the
Universe. Next-generation surveys will maintain this
revolutionary progress. We focus here on the most ambitious
survey currently planned in the visible band, the Large
Synoptic Survey Telescope (LSST). LSST will have unique
survey capability in the faint time domain. The LSST
design is driven by four main science themes: constraining
dark energy and dark matter, taking an inventory of the
Solar System, exploring the transient optical sky, and
mapping the Milky Way. It will be a large, wide-field
ground-based system designed to obtain multiple images
covering the sky that is visible from Cerro Pachón in
Northern Chile. The current baseline design, with an
8.4 m (6.5 m effective) primary mirror, a 9.6 deg2 field
of view, and a 3,200 Megapixel camera, will allow about
10,000 square degrees of sky to be covered using pairs
of 15-second exposures in two photometric bands every
three nights on average. The system is designed to yield
high image quality, as well as superb astrometric and
photometric accuracy. The survey area will include 30,000
deg2 with δ<+34.5°, and will be imaged multiple times
in six bands, ugrizy, covering the wavelength range 320--1050
nm. About 90% of the observing time will be devoted to
a deep-wide-fast survey mode which will observe a 20,000
deg2 region about 1000 times in the six bands during
the anticipated 10 years of operation. These data will
result in databases including 10 billion galaxies and
a similar number of stars, and will serve the majority
of science programs. The remaining 10% of the observing
time will be allocated to special programs such as Very
Deep and Very Fast time domain surveys. We describe how
the LSST science drivers led to these choices of system
parameters.
| Title: |
Measurement of the
Decay B- → D*0e-ν¯e |
| Authors: |
Aubert, B.; Bona, M.; Karyotakis, Y.; Lees, J. P.; Poireau, V.; Prudent, X.; Tisserand, V.; Zghiche, A.; Tico, J. Garra;... Morii, M.;...;
and 536 coauthors. |
| Publication: |
Physical Review Letters,
vol. 100, Issue 23, id. 231803 (PhRvL
Homepage) |
| Publication
Date: |
06/2008 |
| Origin: |
APS |
| Abstract Copyright: |
(c) 2008: The American
Physical Society |
| DOI: |
10.1103/PhysRevLett.100.231803 |
| Bibliographic
Code: |
2008PhRvL.100w1803A |
Abstract:
Using 226×10
6 BBbar events recorded
on the Υ(4S) resonance with the BABAR detector at the
SLAC e
+e
- PEP-II storage rings,
we reconstruct B
-→D
*0e
-ν¯
e decays
using the decay chain D
*0→D
0π
0 and
D
0→K
-π
+. From
the dependence of their differential rate on w, the dot
product of the four velocities of B
- and D
*0,
and using the form factor description by Caprini et al.
with the parameters F(1) and ρ
A12,
we obtain the results ρ
A12=1.16±0.06±0.08,
F(1)|V
cb|=(35.9±0.6±1.4)×10
-3,
and B(B
-→D
*0e
-ν¯
e)=(5.56±0.08±0.41)%.
| Title: |
Search for Resonant ttbar Production
in ppbar Collisions at √8 =1.96
TeV |
| Authors: |
Aaltonen, T.; Abulencia, A.; Adelman, J.; Akimoto, T.; Albrow, M. G.; González, B. Álvarez; Amerio, S.; Amidei, D.; ... Franklin, M.;
... Guimaraes da Costa, J....;
and 604 coauthors. |
| Publication: |
Physical Review Letters,
vol. 100, Issue 23, id. 231803 (PhRvL
Homepage) |
| Publication
Date: |
06/2008 |
| Origin: |
APS |
| Abstract Copyright: |
(c) 2008: The American
Physical Society |
| DOI: |
10.1103/PhysRevLett.100.231803 |
| Bibliographic
Code: |
2008PhRvL.100w1803A |
Abstract:
Using 226×10
6 BBbar; events recorded
on the Υ(4S) resonance with the BABAR detector at the
SLAC e
+e
- PEP-II storage rings,
we reconstruct B
-→D
*0e
-ν¯
e decays
using the decay chain D
*0→D
0π
0 and
D
0→K
-π
+. From
the dependence of their differential rate on w, the dot
product of the four velocities of B
- and D
*0,
and using the form factor description by Caprini et al.
with the parameters F(1) and ρ
A12,
we obtain the results ρ
A12=1.16±0.06±0.08,
F(1)|V
cb|=(35.9±0.6±1.4)×10
-3,
and B(B
-→D
*0e
-ν¯
e)=(5.56±0.08±0.41)%.
Abstract:
Recent schemes for probing non-Abelian statistics in
the quantum Hall effect are based on geometries where
current-carrying quasiparticles flow along edges that
encircle bulk quasiparticles, which are localized. Here
we consider one such scheme, the Fabry-Perot interferometer,
and analyze how its interference patterns are affected
by a coupling that allows tunneling of neutral Majorana
fermions between the bulk and edge. While at weak coupling
this tunneling degrades the interference signal, we find
that at strong coupling, the bulk quasiparticle becomes
essentially absorbed by the edge and the intereference
signal is fully restored. Furthermore, we find that the
strength of the coupling can be tuned by the source-drain
voltage.
Abstract:
Dilute oil dispersions of fractal carbon black particles
with attractive van der Waals interactions display continuous
shear thickening followed by shear thinning at high shear
rates. The shear thickening transition occurs at γ˙
c≅10
2-10
3s
-1
and is driven by hydrodynamic breakup of clusters. Pre-shearing
dispersions at shear rates γ˙>γ˙c produces
enhanced-modulus gels where G'~σ
pre-shear1.5-2 and
is directly proportional to the residual stress in the
gel measured at a fixed sample age. The observed data
can be accounted for using a simple scaling model for
the breakup of fractal clusters under shear stress.
| Title: |
Measurement of the τ-→ηπ-π+π-ντ branching
fraction and a search for a second-class current
in the τ-→η'(958)π-ντ decay |
| Authors: |
Aubert, B.; Bona, M.; Boutigny, D.; Karyotakis, Y.; Lees, J. P.; Poireau, V.; Prudent, X.; Tisserand, V.; Zghiche, A.; Tico, J. ;... Morii, M.;...;
and 556 coauthors. |
| Publication: |
Physical Review D,
vol. 77, Issue 11, id. 112002 (PhRvD
Homepage) |
| Publication
Date: |
06/2008 |
| Origin: |
APS |
| Abstract Copyright: |
(c) 2008: The American
Physical Society |
| DOI: |
10.1103/PhysRevD.77.112002 |
| Bibliographic
Code: |
2008PhRvD..77k2002A |
Abstract:
The τ
-→ηπ
-π
+π
-ν
τ decay
with the η→γγ mode is studied using
384fb
-1 of data collected by the BABAR detector.
The branching fraction is measured to be (1.60±0.05±0.11)×10
-4.
It is found that τ
-→f
1(1285)π
-ν
τ→ηπ
-π
+π
-ν
τ is
the dominant decay mode with a branching fraction of
(1.11±0.06±0.05)×10
-4. The first
error on the branching fractions is statistical and the
second systematic. Note that no particle identification
algorithm is applied to the charged tracks to distinguish
pions from kaons. In addition, a 90% confidence level
upper limit on the branching fraction of the τ
-→η'(958)π
-ν
τdecay
is measured to be 7.2×10-6. This last decay proceeds
through a second-class current and is expected to be
forbidden in the limit of isospin symmetry.
| Title: |
First run II measurement
of the W boson mass at the Fermilab Tevatron |
| Authors: |
Aaltonen, T.; Abulencia, A.; Adelman, J.; Akimoto, T.; Albrow, M. G.; González, B. Álvarez; Amerio, S.; Amidei, D.;
... Franklin, M.;
... Guimaraes da Costa, J....;
and 605 coauthors. |
| Publication: |
Physical Review D,
vol. 77, Issue 11, id. 112001 (PhRvD
Homepage) |
| Publication
Date: |
06/2008 |
| Origin: |
APS |
| Abstract Copyright: |
(c) 2008: The American
Physical Society |
| DOI: |
10.1103/PhysRevD.77.112001 |
| Bibliographic
Code: |
2008PhRvD..77k2001A |
Abstract:
We describe a measurement of the W boson mass mW using
200pb-1 of s=1.96TeV p&pmacr; collision data taken
with the CDF II detector. With a sample of 63 964 W→eν
candidates and 51 128 W→μν candidates, we measure
mW=[80.413±0.034(stat)±0.034(sys)=80.413±0.048]GeV/c2.
This is the single most precise mW measurement to date.
When combined with other measured electroweak parameters,
this result further constrains the properties of new
unobserved particles coupling to W and Z bosons.
Abstract:
We introduce a new class of sine-Gordon models, for which
the interaction term is present in a region different
from the domain over which the quadratic part is defined.
We develop a nonperturbative approach for calculating
partition functions of such models, which relies on mapping
them to statistical properties of random surfaces. As
a specific application of our method, we consider the
problem of calculating the amplitude of interference
fringes in experiments with two independent low dimensional
Bose gases. We calculate full distribution functions
of interference amplitude for one-dimensional and two-dimensional
gases with nonzero temperatures.
Abstract:
We analyze cavity-assisted cooling schemes for polar
molecules in the microwave domain, where molecules are
excited on a rotational transition and energy is dissipated
via strong interactions with a lossy stripline cavity,
as recently proposed by André et al 2006 Nat. Phys. 2
636. We identify the dominant cooling and heating mechanisms
in this setup and study cooling rates and final temperatures
in various parameter regimes. In particular, we analyze
the effects of a finite environment temperature on the
cooling efficiency, and find minimal temperature and
optimized cooling rate in the strong drive regime. Further,
we discuss the trade-off between efficiency of cavity
cooling and robustness with respect to ubiquitous imperfections
in a realistic experimental setup, such as anharmonicity
of the trapping potential.
| Title: |
Surface physics:
Electron wrangling in quantum corrals |
| Authors: |
Heller, Eric J. |
| Publication: |
Nature Physics, Volume
4, Issue 6, pp. 443-444 (2008). |
| Publication
Date: |
06/2008 |
| Origin: |
NATURE |
| Abstract
Copyright: |
(c) 2008: Nature |
| DOI: |
10.1038/nphys991 |
| Bibliographic
Code: |
2008NatPh...4..443H |
Abstract:
Unprecedented control over the superposition of electronic
states in a 'quantum corral', exerted by changing the
position of a single atom within it, provides a powerful
tool for studying the quantum behaviour of matter.
| Title: |
Anyonic interferometry
and protected memories in atomic spin lattices |
| Authors: |
Jiang, Liang; Brennen, Gavin K.; Gorshkov, Alexey V.; Hammerer, Klemens; Hafezi, Mohammad; Demler, Eugene; Lukin, Mikhail D.; Zoller, Peter |
| Publication: |
Nature Physics, Volume
4, Issue 6, pp. (2008). |
| Publication
Date: |
06/2008 |
| Origin: |
NATURE |
| Abstract
Copyright: |
(c) 2008: Nature |
| DOI: |
10.1038/nphys943 |
| Bibliographic
Code: |
2008NatPh...4.....J |
Abstract:
Strongly correlated quantum systems can exhibit exotic
behaviour called topological order which is characterized
by non-local correlations that depend on the system topology.
Such systems can exhibit remarkable phenomena such as
quasiparticles with anyonic statistics and have been
proposed as candidates for naturally error-free quantum
computation. However, anyons have never been observed
in nature directly. Here, we describe how to unambiguously
detect and characterize such states in recently proposed
spin-lattice realizations using ultracold atoms or molecules
trapped in an optical lattice. We propose an experimentally
feasible technique to access non-local degrees of freedom
by carrying out global operations on trapped spins mediated
by an optical cavity mode. We show how to reliably read
and write topologically protected quantum memory using
an atomic or photonic qubit. Furthermore, our technique
can be used to probe statistics and dynamics of anyonic
excitations.
| Title: |
Probing quantum and
thermal noise in an interacting many-body system |
| Authors: |
Hofferberth, S.; Lesanovsky, I.; Schumm, T.; Imambekov, A.; Gritsev, V.; Demler, E.; Schmiedmayer, J. |
| Publication: |
Nature Physics, Volume
4, Issue 6, pp. (2008). |
| Publication
Date: |
06/2008 |
| Origin: |
NATURE |
| Abstract
Copyright: |
(c) 2008: Nature |
| DOI: |
10.1038/nphys941 |
| Bibliographic
Code: |
2008NatPh...4.....H |
Abstract:
The probabilistic character of the measurement process
is one of the most puzzling and fascinating aspects of
quantum mechanics. In many-body systems quantum-mechanical
noise reveals non-local correlations of the underlying
many-body states. Here, we provide a complete experimental
analysis of the shot-to-shot variations of interference-fringe
contrast for pairs of independently created one-dimensional
Bose condensates. Analysing different system sizes, we
observe the crossover from thermal to quantum noise,
reflected in a characteristic change in the distribution
functions from poissonian to Gumbel type, in excellent
agreement with theoretical predictions on the basis of
the Luttinger-liquid formalism. We present the first
experimental observation of quasi-long-range order in
one-dimensional atomic condensates, which is a hallmark
of quantum fluctuations in one-dimensional systems. Furthermore,
our experiments constitute the first analysis of the
full distribution of quantum noise in an interacting
many-body system.
Abstract:
The MSSM can arise as an orientifold of a pyramid-like
quiver in the context of intersecting D-branes. Here
we consider quiver realizations of the MSSM which can
emerge at the bottom of a duality cascade. We classify
all possible minimal ways this can be done by allowing
only one extra node. It turns out that this requires
extending the geometry of the pyramid to an octahedron.
The MSSM at the bottom of the cascade arises in one of
two possible ways, with the extra node disappearing either
via Higgsing or confinement. Remarkably, the quiver of
the Higgsing scenario turns out to be nothing but the
quiver version of the left-right symmetric extension
of the MSSM. In the minimal confining scenario the duality
cascade can proceed if and only if there is exactly one
up/down Higgs pair. Moreover, the symmetries of the octahedron
naturally admit an automorphism of the quiver which solves
a version of the μ problem precisely when there are an
odd number of generations.
| Title: |
Photon generation
from vacuum in non-stationary circuit QED |
| Authors: |
Dodonov, A. V.; Celeri, L. C.; Pascoal, F.; Lukin, M. D.; Yelin, S. F. |
| Publication: |
eprint arXiv:0806.4035 |
| Publication
Date: |
06/2008 |
| Origin: |
ARXIV |
| Keywords: |
Quantum Physics |
| Comment: |
7 pages, 3 figures |
| Bibliographic
Code: |
2008arXiv0806.4035D |
Abstract:
We study theoretically the solid state cavity QED systems
in which the artificial atom transition frequency has
a small periodic modulation in time. The system formed
by the artificial atom coupled to a single cavity mode
is described by the Rabi Hamiltonian. We show that when
the modulation of the atomic transition frequency meets
the `resonance' conditions the dynamics of the system
may be described effectively by well known Hamiltonians
- Dynamical Casimir effect, Jaynes-Cummings or Anti-Jaynes-Cummings
Hamiltonians - for arbitrary (large) atom-cavity detuning.
Thus photons, as well as atomic excitations, may be generated
from vacuum due to the dynamical Casimir effect via the
modulation of a single two-level atom.
| Title: |
Quantum quasiresonances
in grazing incident angle atom-surface collisions |
| Authors: |
Ruiz, Antonia; Palao, Jose P.; Heller, Eric J. |
| Publication: |
eprint arXiv:0806.3866 |
| Publication
Date: |
06/2008 |
| Origin: |
ARXIV |
| Keywords: |
Quantum Physics |
| Comment: |
4 pages, 3 figures |
| Bibliographic
Code: |
2008arXiv0806.3866R |
Abstract:
The momentum transfer between the normal components to
an index direction in the collision of an atom with a
periodic surface is investigated. For fast atoms with
grazing angle of incidence there is an interval of azimuthal
angles around the index direction for which the energy
transfer can be very efficient. This effect is reflected
in quantum diffraction patterns with large non-specular
peaks, associated with the parallel to the surface and
normal to the index direction momentum component, and
can be described in terms of quasiresonance. Although
the classical dynamics does not reproduce the precise
quantum diffraction probabilities, indicating the quantum
nature of this effect, classical and quantum computations
show that the span of the quasiresonance region coincides
in both dynamics and can be classically estimated from
the phase-space analysis.
Abstract:
We describe a technique that enables a strong, coherent
coupling between a single electronic spin qubit associated
with a nitrogen-vacancy impurity in diamond and the quantized
motion of a magnetized nano-mechanical resonator tip.
This coupling is achieved via careful preparation of
dressed spin states which are highly sensitive to the
motion of the resonator but insensitive to perturbations
from the nuclear spin bath. In combination with optical
pumping techniques, the coherent exchange between spin
and motional excitations enables ground state cooling
and the controlled generation of arbitrary quantum superpositions
of resonator states. Optical spin readout techniques
provide a general measurement toolbox for the resonator
with quantum limited precision.
| Title: |
Effective hamiltonian
for FeAs based superconductors |
| Authors: |
Manousakis, Efstratios; Ren, Jun; Kaxiras, Efthimios |
| Publication: |
eprint arXiv:0806.3432 |
| Publication
Date: |
06/2008 |
| Origin: |
ARXIV |
| Keywords: |
Condensed Matter
- Strongly Correlated Electrons, Condensed Matter
- Superconductivity |
| Comment: |
9 pages, 5 figures |
| Bibliographic
Code: |
2008arXiv0806.3432M |
Abstract:
The recently discovered FeAs-based superconductors show
intriguing behavior and unusual dynamics of electrons
and holes which occupy the Fe d-orbitals and As 4s and
4p orbitals. Starting from the atomic limit, we carry
out a strong coupling expansion to derive an effective
hamiltonian that describes the electron and hole behavior.
The hopping and the hybridization parameters between
the Fe d- and As s- and p-orbitals are obtained by fitting
the results of our calculations based on the local density
approximation to a tight-binding model which involves
these as fitting parameters. We find that the effective
hamiltonian, in the strong on-site Coulomb repulsion
limit, consists of three parts which operate on three
distinct sub-spaces coupled through Hund's rule. The
three sub-spaces describe different components (or subsystems):
(a) one spanned by the degenerate atomic Fe orbitals
$d_{xz}$ and $d_{yz}$; (b) one spanned by the atomic
Fe orbitals $d_{xy}$ and $d_{z^2}$; and (c) one spanned
by the $d_{x^2-y^2}$ Fe orbital. Each of these hamiltonians
is an extended t-t'-J-J' model and is characterized by
different coupling constants and filling factors. For
the case of the undoped material we argue that the first
component alone prefers a ground state characterized
by a spin-density-wave order similar to that observed
in recent experimental studies, while the other two subspaces
prefer an antiferromagnetic order. We also argue that
the observed spin-density-wave order serves as a compromise
state that minimizes the ground state energy of the total
hamiltonian.
| Title: |
Hydrodynamic attraction
of swimming microorganisms by surfaces |
| Authors: |
Berke, Allison P.; Turner, Linda; Berg, Howard C.; Lauga, Eric |
| Publication: |
eprint arXiv:0806.2898 |
| Publication
Date: |
06/2008 |
| Origin: |
ARXIV |
| Keywords: |
Condensed Matter
- Soft Condensed Matter, Physics - Biological
Physics, Physics - Fluid Dynamics |
| Bibliographic
Code: |
2008arXiv0806.2898B |
Abstract:
Cells swimming in confined environments are attracted
by surfaces. We measure the steady-state distribution
of smooth-swimming bacteria (Escherichia coli) between
two glass plates. In agreement with earlier studies,
we find a strong increase of the cell concentration at
the boundaries. We demonstrate theoretically that hydrodynamic
interactions of the swimming cells with solid surfaces
lead to their re-orientation in the direction parallel
to the surfaces, as well as their attraction by the closest
wall. A model is derived for the steady-state distribution
of swimming cells, which compares favorably with our
measurements. We exploit our data to estimate the flagellar
propulsive force in swimming E. coli.
| Title: |
Roton softening and
supersolidity in Rb spinor condensates |
| Authors: |
Cherng, R. W.; Demler, E. |
| Publication: |
eprint arXiv:0806.1991 |
| Publication
Date: |
06/2008 |
| Origin: |
ARXIV |
| Keywords: |
Condensed Matter
- Other |
| Comment: |
8 pages, 5 figures |
| Bibliographic
Code: |
2008arXiv0806.1991C |
Abstract:
Superfluids with a tendency towards periodic crystalline
order have both a phonon and roton like spectrum of collective
modes. The softening of the roton spectrum provides one
route to a supersolid. We show that roton softening occurs
in 87Rb spinor condensates once dipolar interactions
and spin dynamics are taken into account. By including
the effects of a quasi-two-dimensional geometry and rapid
Larmor precession, we show a dynamical instability develops
in the collective mode spectrum at finite wavevectors.
We construct phase diagrams showing a variety of instabilities
as a function of the direction of the magnetic field
and strength of the quadratic Zeeman shift. Our results
provide a possible explanation of current experiments
in the Berkeley group Phys. Rev. Lett. 100:170403 (2008).
| Title: |
Are Microwave Induced
Zero Resistance States Necessarily Static? |
| Authors: |
Finkler, Ilya G.; Halperin, Bertrand I. |
| Publication: |
eprint arXiv:0806.1562 |
| Publication
Date: |
06/2008 |
| Origin: |
ARXIV |
| Keywords: |
Condensed Matter
- Mesoscopic Systems and Quantum Hall Effect |
| Comment: |
Submitted to PRB |
| Bibliographic
Code: |
2008arXiv0806.1562F |
Abstract:
We study the effect of inhomogeneities in Hall conductivity
on the nature of the Zero Resistance States seen in the
microwave irradiated two-dimensional electron systems
in weak perpendicular magnetic fields, and we show that
time-dependent domain patterns may emerge in some situations.
For an annular Corbino geometry, with an equilibrium
charge density that varies linearly with radius, we find
a time-periodic non-equilibrium solution, which might
be detected by a charge sensor, such as an SET. For a
model on a torus, in addition to static domain patterns
seen at high and low values of the equilibrium charge
inhomogeneity, we find that, in the intermediate regime,
a variety of nonstationary states can also exist. We
catalog the possibilities we have seen in our simulations.
Within a particular phenomenological model, we show that
linearizing the nonlinear charge continuity equation
about a particularly simple domain wall configuration
and analyzing the eigenmodes allows us to estimate the
periods of the solutions to the full nonlinear equation.
Abstract:
The cross-correlation between high redshift galaxies
and 21 cm emission from the high redshift intergalactic
medium (IGM) promises to be an excellent probe of the
Epoch of Reionization (EoR). On large scales, the 21
cm and galaxy fields are anti-correlated during most
of the reionization epoch. However, on scales smaller
than the size of the H II regions around detectable galaxies,
the two fields become roughly uncorrelated. Consequently,
the 21 cm-galaxy cross power spectrum provides a tracer
of bubble growth during reionization, with the signal
turning over on progressively larger scales as reionization
proceeds. The precise turnover scale depends on the minimum
host mass of the detectable galaxies, and the galaxy
selection technique. Measuring the turnover scale as
a function of galaxy luminosity constrains the characteristic
bubble size around galaxies of different luminosities.
The cross spectrum becomes positive on small scales if
ionizing photons fail to escape from low mass galaxies,
and these galaxies are detectable longward of the hydrogen
ionization edge, because in this case some identifiable
galaxies lie outside of ionized regions. LOFAR can potentially
measure the 21 cm-galaxy cross spectrum in conjunction
with mild extensions to the existing Subaru survey for
$z=6.6$ Lyman-alpha emitters, while the MWA is slightly
less sensitive for detecting the cross spectrum. A futuristic
galaxy survey covering a sizable fraction of the MWA
field of view ($\sim 800$ deg$^2$) can probe the scale
dependence of the cross spectrum, constraining the filling
factor of H II regions at different redshifts during
reionization, and providing other valuable constraints
on reionization models.
| Title: |
Dijet Searches for
Supersymmetry at the LHC |
| Authors: |
Randall, Lisa; Tucker-Smith, David |
| Publication: |
eprint arXiv:0806.1049 |
| Publication
Date: |
06/2008 |
| Origin: |
ARXIV |
| Keywords: |
High Energy Physics
- Phenomenology, High Energy Physics - Experiment |
| Bibliographic
Code: |
2008arXiv0806.1049R |
Abstract:
We present several strategies for searching for supersymmetry
in dijet channels that do not explicitly invoke missing
energy. Preliminary investigations suggest that signal-to-background
ratios of at least 4--5 should be achievable at the LHC,
with discovery possible for squarks as heavy as ~ 1.7
TeV.
| Title: |
Signatures of neutral
quantum Hall modes in transport through low-density
constrictions |
| Authors: |
Rosenow, Bernd; Halperin, Bertrand I. |
| Publication: |
eprint arXiv:0806.0869 |
| Publication
Date: |
06/2008 |
| Origin: |
ARXIV |
| Keywords: |
Condensed Matter
- Mesoscopic Systems and Quantum Hall Effect,
Condensed Matter - Disordered Systems and Neural
Networks, Condensed Matter - Strongly Correlated
Electrons |
| Comment: |
corrected description
of the results of Ref. [10], Ref. [17] added |
| Bibliographic
Code: |
2008arXiv0806.0869R |
Abstract:
Constrictions in fractional quantum Hall (FQH) systems
not only facilitate backscattering between counter-propagating
edge modes, but also may reduce the constriction filling
fraction $\nu_c$ with respect to the bulk filling fraction
$\nu_b$. If both $\nu_b$ and $\nu_c$ correspond to incompressible
FQH states, at least part of the constriction region
is surrounded by composite edges, whose low energy dynamics
is characterized by a charge mode and one or several
neutral modes. In the incoherent regime, decay of neutral
modes describes the equilibration of composite FQH edges,
while in the limit of coherent transport, the presence
of neutral modes gives rise to universal conductance
fluctuations. In addition, neutral modes renormalize
the strength of scattering across the constriction, and
thus can determine the relative strength of forward and
backwards scattering.
Abstract:
We suggest and analyze a novel technique for efficient
and robust creation of dense ultracold molecular ensembles
in their ground rovibrational state. In our approach
a molecule is brought to the ground state through a series
of intermediate vibrational states via a {\em multistate
chainwise Stimulated Raman Adiabatic Passage} (c-STIRAP)
technique. We study the influence of the intermediate
states decay on the transfer process and suggest an approach
that minimizes the population of these states, resulting
in a maximal transfer efficiency. As an example, we analyze
the formation of $^{87}$Rb$_{2}$ starting from an initial
Feshbach molecular state and taking into account major
decay mechanisms due to inelastic atom-molecule and molecule-molecule
collisions. Numerical analysis suggests a transfer efficiency
$>$ 90%, even in the presence of strong collisional
relaxation as are present in a high density atomic gas.
| Title: |
A Flat Photoionization
Rate at 2<z<4.2: Evidence for a Stellar-Dominated
UV Background and Against a Decline of Cosmic
Star Formation Beyond z~3 |
| Authors: |
Faucher-Giguere, C. -A.; Lidz, A.; Hernquist, L.; Zaldarriaga, M. |
| Publication: |
eprint arXiv:0806.0372 |
| Publication
Date: |
06/2008 |
| Origin: |
ARXIV |
| Keywords: |
Astrophysics |
| Comment: |
5 pages, including
1 figure, accepted by ApJ Letters; corrected
minor plotting mistake in the figure |
| Bibliographic
Code: |
2008arXiv0806.0372F |
Abstract:
We investigate the implications of our measurement of
the Lyman-alpha forest opacity at redshifts 2<z<4.2
from a sample of 86 high-resolution quasar spectra for
the evolution of the cosmic ultraviolet luminosity density
and its sources. The derived hydrogen photoionization
rate is remarkably flat over this redshift range, implying
an increasing comoving ionizing emissivity with redshift.
Because the quasar luminosity function is strongly peaked
near z~2, star-forming galaxies likely dominate the ionizing
emissivity at z>~3. Our measurement argues against
a star formation rate density declining beyond z~3, in
contrast with existing state-of-the-art determinations
of the cosmic star formation history from direct galaxy
counts. Stellar emission from galaxies therefore likely
reionized the Universe.
| Title: |
Preparation and detection
of d-wave superfluidity in two-dimensional optical
superlattices |
| Authors: |
Rey, A. M.; Sensarma, R.; Foelling, S.; Greiner, M.; Demler, E.; Lukin, M. D. |
| Publication: |
eprint arXiv:0806.0166 |
| Publication
Date: |
06/2008 |
| Origin: |
ARXIV |
| Keywords: |
Condensed Matter
- Other |
| Comment: |
8 pages, 6 figures |
| Bibliographic
Code: |
2008arXiv0806.0166R |
Abstract:
We propose a controlled method to create and detect d-wave
superfluidity with ultracold fermionic atoms loaded in
two-dimensional optical superlattices. Our scheme consists
in preparing an array of nearest-neighbor coupled square
plaquettes or "superplaquettes" and using them
as building blocks to construct a d-wave superfluid state.
We describe how to use the coherent dynamical evolution
in such a system to experimentally probe the pairing
mechanism. We also derive the zero temperature phase
diagram of the fermions in a checkerboard lattice (many
weakly coupled plaquettes) and show that by tuning the
inter-plaquette tunneling spin-dependently or varying
the filling factor one can drive the system into a d-wave
superfluid phase or a Cooper pair density wave phase.
We discuss the use of noise correlation measurements
to experimentally probe these phases.
| Title: |
GUTs and Exceptional
Branes in F-theory - II: Experimental Predictions |
| Authors: |
Beasley, Chris; Heckman, Jonathan J.; Vafa, Cumrun |
| Publication: |
eprint arXiv:0806.0102 |
| Publication
Date: |
06/2008 |
| Origin: |
ARXIV |
| Keywords: |
High Energy Physics
- Theory, High Energy Physics - Phenomenology |
| Comment: |
v2: 203 pages, 8
figures, typos corrected, references added, revised
figure and discussion of minimal flipped SU(5)
scenario |
| Bibliographic
Code: |
2008arXiv0806.0102B |
Abstract:
We consider realizations of GUT models in F-theory. Adopting
a bottom up approach, the assumption that the dynamics
of the GUT model can in principle decouple from Planck
scale physics leads to a surprisingly predictive framework.
An internal U(1) hypercharge flux Higgses the GUT group
directly to the MSSM or to a flipped GUT model, a mechanism
unavailable in heterotic models. This new ingredient
automatically addresses a number of puzzles present in
traditional GUT models. The internal U(1) hyperflux allows
us to solve the doublet-triplet splitting problem, and
explains the qualitative features of the distorted GUT
mass relations for lighter generations due to the Aharanov-Bohm
effect. These models typically come with nearly exact
global symmetries which prevent bare mu terms and also
forbid dangerous baryon number violating operators. Strong
curvature around our brane leads to a repulsion mechanism
for Landau wave functions for neutral fields. This leads
to large hierarchies of the form exp(-c/B^(2*g)) where
c and g are order one parameters and B ~ M_(GUT)/(M_(pl)*alpha_(GUT)).
This effect can simultaneously generate a viably small
mu term as well as an acceptable Dirac neutrino mass
on the order of 0.5 * 10^(-2 +/- 0.5) eV. In another
scenario, we find a modified seesaw mechanism which predicts
that the light neutrinos have masses in the expected
range while the Majorana mass term for the heavy neutrinos
is ~ 3 * 10^(12 +/- 1.5) GeV. Communicating supersymmetry
breaking to the MSSM can be elegantly realized through
gauge mediation. In one scenario, the same repulsion
mechanism also leads to messenger masses which are naturally
much lighter than the GUT scale.
| Title: |
Spectral
Identification of an Ancient Supernova Using
Light Echoes in the Large Magellanic Cloud |
| Authors: |
Rest, A.; Matheson, T.; Blondin, S.; Bergmann, M.; Welch, D. L.; Suntzeff, N. B.; Smith, R. C.; Olsen, K.; Prieto, J. L.; Garg, A.; Challis, P.; Stubbs, C.; Hicken, M.; Modjaz, M.; Wood-Vasey, W. M.; Zenteno, A.; Damke, G.; Newman, A.; Huber, M.; Cook, K. H.; Nikolaev, S.; Becker, A. C.; Miceli, A.; Covarrubias, R.; Morelli, L.; Pignata, G.; Clocchiatti, A.; Minniti, D.; Foley, R. J. |
| Publication: |
The Astrophysical
Journal, Volume 680, Issue 2, pp. 1137-1148.
(ApJ
Homepage) |
| Publication
Date: |
06/2008 |
| Origin: |
UCP |
| ApJ Keywords: |
ISM: Individual:
Alphanumeric: SNR 0509-67.5, Galaxies: Magellanic
Clouds, Stars: Supernovae: General, ISM: Supernova
Remnants |
| Abstract
Copyright: |
(c) 2008: Spectral
Identification of an Ancient Supernova Using
Light Echoes in the Large Magellanic Cloud |
| DOI: |
10.1086/587158 |
| Bibliographic
Code: |
2008ApJ...680.1137R |
Abstract:
We report the successful identification of the type of
the supernova (SN) responsible for the supernova remnant
SNR 0509-675 in the Large Magellanic Cloud (LMC) using
Gemini spectra of surrounding light echoes. The ability
to classify outbursts associated with centuries-old remnants
provides a new window into several aspects of SN research
and is likely to be successful in providing new constraints
on additional LMC SNe, as well as their historical counterparts
in the Milky Way (MW). The combined spectrum of echo
light from SNR 0509-675 shows broad emission and absorption
lines consistent with a SN spectrum. We create a spectral
library consisting of 28 SNe Ia and 6 SNe Ib/c that are
time-integrated, dust-scattered by LMC dust, and reddened
by the LMC and MW. We fit these SN templates to the observed
light echo spectrum using χ2 minimization, as well as
correlation techniques, and we find that overluminous
1991T-like SNe Ia with Δm15<0.9 match the observed
spectrum best.
Abstract:
Quasi-particles with fractional charge and statistics,
as well as modified Coulomb interactions, exist in a
two-dimensional electron system in the fractional quantum
Hall (FQH) regime. Theoretical models of the FQH state
at filling fraction ν=52 make the further prediction
that the wave function can encode the interchange of
two quasi-particles, making this state relevant for topological
quantum computing. We show that bias-dependent tunneling
across a narrow constriction at ν=52 exhibits temperature
scaling and, from fits to the theoretical scaling form,
extract values for the effective charge and the interaction
parameter of the quasi-particles. Ranges of values obtained
are consistent with those predicted by certain models
of the 52 state.
| Title: |
Search for the Higgs
Boson in Events with Missing Transverse Energy
and b Quark Jets Produced in p&pmacr; Collisions
at s=1.96TeV |
| Authors: |
Aaltonen, T.; Adelman, J.; Akimoto, T.; Albrow, M. G.; Álvarez González, B.; Amerio, S.; Amidei, D.; Anastassov, A.; ... Franklin, M.;
... Guimaraes da Costa, J....;
and 609 coauthors. |
| Publication: |
Physical Review Letters,
vol. 100, Issue 21, id. 211801 (PhRvL
Homepage) |
| Publication
Date: |
05/2008 |
| Origin: |
APS |
| Abstract Copyright: |
(c) 2008: The American
Physical Society |
| DOI: |
10.1103/PhysRevLett.100.211801 |
| Bibliographic
Code: |
2008PhRvL.100u1801A |
Abstract:
We search for the standard model Higgs boson produced
in association with an electroweak vector boson in events
with no identified charged leptons, large imbalance in
transverse momentum, and two jets where at least one
contains a secondary vertex consistent with the decay
of b hadrons. We use ˜1fb-1 integrated luminosity of
p&pmacr; collisions at s=1.96TeV recorded by the
Collider Detector at Fermilab II experiment at
