2,616 research outputs found
The LHC Phenomenology of Vectorlike Confinement
Full text linkWe investigate in detail the LHC phenomenology of "vectorlike confinement",
where the Standard Model is augmented by a new confining gauge interaction and
new light fermions that carry vectorlike charges under both the Standard Model
and the new gauge group. If the new interaction confines at the TeV scale, this
framework gives rise to a wide range of exotic collider signatures such as the
production of a vector resonance that decays to a pair of collider-stable
charged massive particles (a "di-CHAMP" resonance), to a pair of
collider-stable massive colored particles (a "di-R-hadron resonance), to
multiple photons, s and s via two intermediate scalars, and/or to
multi-jet final states. To study these signals at the LHC, we set up two
benchmark models: one for the di-CHAMP and multi-photon signals, and the other
for the di-R-hadron and multijet signals. For the di-CHAMP/multi-photon model,
Standard Model backgrounds are negligible, and we show that a full
reconstruction of the spectrum is possible, providing powerful evidence for
vectorlike confinement. For the di-R-hadron/multijet model, we point out that
in addition to the di-R-hadron signal, the rate of the production of four
R-hadrons can also be sizable at the LHC. This, together with the multi-jet
signals studied in earlier work, makes it possible to single out vectorlike
confinement as the underlying dynamics.Comment: 32 pages, 28 figures. Several typos fixed, one paragraph added
elaborating choice of benchmarks. Version accepted by JHEP
Variable and reversible quantum structures on a single carbon nanotube
Get PDFThe band gap of a semiconducting single wall carbon nanotube decreases and
eventually vanishes leading to metalization as a result of increasing radial
deformation. This sets in a band offset between the undeformed and deformed
regions of a single nanotube. Based on the superlattice calculations, we show
that these features can be exploited to realize various quantum well structures
on a single nanotube with variable and reversible electronic properties. These
quantum structures and nanodevices incorporate mechanics and electronics.Comment: 7 pages, 4 figures, To be appear in PR
Feshbach Resonance and Growth of a Bose-Einstein Condensate
Full text linkGross-Pitaevskii equation with gain is used to model Bose Einstein
condensation (BEC) fed by the surrounding thermal cloud. It is shown that the
number of atoms continuously injected into BEC from the reservoir can be
controlled by applying the external magnetic field via Feshbach resonance.Comment: 4 page
A Detailed Model Atmosphere Analysis of Cool White Dwarfs in the Sloan Digital Sky Survey
Get PDFWe present optical spectroscopy and near-infrared photometry of 126 cool
white dwarfs in the Sloan Digital Sky Survey (SDSS). Our sample includes high
proper motion targets selected using the SDSS and USNO-B astrometry and a dozen
previously known ultracool white dwarf candidates. Our optical spectroscopic
observations demonstrate that a clean selection of large samples of cool white
dwarfs in the SDSS (and the SkyMapper, Pan-STARRS, and the Large Synoptic
Survey Telescope datasets) is possible using a reduced proper motion diagram
and a tangential velocity cut-off (depending on the proper motion accuracy) of
30 km/s. Our near-infrared observations reveal eight new stars with significant
absorption. We use the optical and near-infrared photometry to perform a
detailed model atmosphere analysis. More than 80% of the stars in our sample
are consistent with either pure hydrogen or pure helium atmospheres. However,
the eight stars with significant infrared absorption and the majority of the
previously known ultracool white dwarf candidates are best explained with mixed
hydrogen and helium atmosphere models. The age distribution of our sample is
consistent with a Galactic disk age of 8 Gyr. A few ultracool white dwarfs may
be as old as 12-13 Gyr, but our models have problems matching the spectral
energy distributions of these objects. There are only two halo white dwarf
candidates in our sample. However, trigonometric parallax observations are
required for accurate mass and age determinations and to confirm their
membership in the halo.Comment: ApJ Supplements, in pres
Skew-Flavored Dark Matter
Full text linkWe explore a novel flavor structure in the interactions of dark matter with
the Standard Model. We consider theories in which both the dark matter
candidate, and the particles that mediate its interactions with the Standard
Model fields, carry flavor quantum numbers. The interactions are skewed in
flavor space, so that a dark matter particle does not directly couple to the
Standard Model matter fields of the same flavor, but only to the other two
flavors. This framework respects Minimal Flavor Violation, and is therefore
naturally consistent with flavor constraints. We study the phenomenology of a
benchmark model in which dark matter couples to right-handed charged leptons.
In large regions of parameter space the dark matter can emerge as a thermal
relic, while remaining consistent with the constraints from direct and indirect
detection. The collider signatures of this scenario include events with
multiple leptons and missing energy. These events exhibit a characteristic
flavor pattern that may allow this class of models to be distinguished from
other theories of dark matter.Comment: 10 pages, 7 figures. v2: Discussion of collider signatures expanded,
added new section on alternative flavor structures, other minor changes.
Matches published versio
First Results from Pan-STARRS1: Faint, High Proper Motion White Dwarfs in the Medium-Deep Fields
Full text linkThe Pan-STARRS1 survey has obtained multi-epoch imaging in five bands
(Pan-STARRS1 gps, rps, ips, zps, and yps) on twelve "Medium Deep Fields", each
of which spans a 3.3 degree circle. For the period between Apr 2009 and Apr
2011 these fields were observed 50-200 times. Using a reduced proper motion
diagram, we have extracted a list of 47 white dwarf (WD) candidates whose
Pan-STARRS1 astrometry indicates a non-zero proper motion at the 6-sigma level,
with a typical 1-sigma proper motion uncertainty of 10 mas/yr. We also used
astrometry from SDSS (when available) and USNO-B to assess our proper motion
fits. None of the WD candidates exhibits evidence of statistically significant
parallaxes, with a typical 1-sigma uncertainty of 8 mas. Twelve of these
candidates are known WDs, including the high proper motion (1.7"/yr) WD LHS
291. We confirm three more objects as WDs through optical spectroscopy. Based
on the Pan-STARRS1 colors, ten of the stars are likely to be cool WDs with 4170
K Teff 5000 K and cooling ages <9 Gyr. We classify these objects as likely
thick disk WDs based on their kinematics. Our current sample represents only a
small fraction of the Pan-STARRS1 data. With continued coverage from the Medium
Deep Field Survey and the 3pi survey, Pan-STARRS1 should find many more high
proper motion WDs that are part of the old thick disk and halo.Comment: 33 pages, 8 figures, submitted to Ap
Searching for Multijet Resonances at the LHC
Full text linkRecently it was shown that there is a class of models in which colored vector
and scalar resonances can be copiously produced at the Tevatron with decays to
multijet final states, consistent with all experimental constraints and having
strong discovery potential. We investigate the collider phenomenology of TeV
scale colored resonances at the LHC and demonstrate a strong discovery
potential for the scalars with early data as well as the vectors with
additional statistics. We argue that the signal can be self-calibrating and
using this fact we propose a search strategy which we show to be robust to
systematic errors typically expected from Monte Carlo background estimates. We
model the resonances with a phenomenological Lagrangian that describes them as
bound states of colored vectorlike fermions due to new confining gauge
interactions. However, the phenomenological Lagrangian treatment is quite
general and can represent other scenarios of microscopic physics as well.Comment: 28 pages, 13 figures, pdflatex. Discussion of background expanded,
minor modifications made. Version to appear in JHE
Echoes of a decaying planetary system: the gaseous and dusty disks surrounding three white dwarfs
Full text linkWe have performed a comprehensive ground-based observational program aimed at
characterizing the circumstellar material orbiting three single white dwarf
stars previously known to possess gaseous disks. Near-infrared imaging
unambiguously detects excess infrared emission towards Ton 345 and allows us to
refine models for the circumstellar dust around all three white dwarf stars. We
find that each white dwarf hosts gaseous and dusty disks that are roughly
spatially coincident, a result that is consistent with a scenario in which
dusty and gaseous material has its origin in remnant parent bodies of the white
dwarfs' planetary systems. We briefly describe a new model for the gas disk
heating mechanism in which the gaseous material behaves like a "Z II" region.
In this Z II region, gas primarily composed of metals is photoionized by
ultraviolet light and cools through optically thick allowed Ca II-line
emission.Comment: 43 pages, 9 tables, 9 figures. Accepted to Ap
Recommended from our members
Factors associated with extended remission in neovascular age-related macular degeneration on pro re nata treatment protocol.
Get PDFAimTo show the characteristics and outcomes of patients with neovascular age-related macular degeneration (nAMD) who had extended remission (ER) while on a pro re nata (PRN) treatment protocol.MethodsThis was a retrospective case-control study of a consecutive series of patients with nAMD treated with a PRN antivascular endothelial growth factor (anti-VEGF) drug regimen. ER was defined as the absence of haemorrhage, intraretinal/subretinal fluid on optical coherence tomography and leakage on fluorescein angiography for 52 weeks after cessation of anti-VEGF therapy. Matching patients with nAMD who did not achieve ER were included as control group. Cox regression analysis was fitted to identify predictors of time to achieve ER and time to recurrence. A logistic regression analysis of baseline characteristics was used to identify predictors of achieving ER.ResultsOf 830 eyes treated with anti-VEGF monotherapy, 77 (9.2%) eyes achieved ER during a median follow-up of 236 weeks (range 70-525 weeks). Cox regression analysis showed that ER was achieved earlier in eyes with isolated intraretinal fluid (HR, 2.05; 95% CI 1.929 to 4.520; p=0.045) at presentation. Logistic regression analysis showed that type 3 choroidal neovascularisation (OR, 0.090; 95% CI 0.021 to 0.382; p=0.001), thinner choroid (OR, 0.993; 95% CI 0.988 to 0.998; p=0.004) and absence of macular atrophy (OR, 0.233; 95% CI 0.065 to 0.839; p=0.026) at baseline increased the likelihood of achieving ER.ConclusionER is achievable in 9.2% of patients under PRN therapy for nAMD. At presentation with nAMD, anatomical features on retinal imaging may predict the likelihood of achieving ER and a shorter time to achieve ER
- …
