2,001 research outputs found
Origins of Hidden Sector Dark Matter I: Cosmology
We present a systematic cosmological study of a universe in which the visible
sector is coupled, albeit very weakly, to a hidden sector comprised of its own
set of particles and interactions. Assuming that dark matter (DM) resides in
the hidden sector and is charged under a stabilizing symmetry shared by both
sectors, we determine all possible origins of weak-scale DM allowed within this
broad framework. We show that DM can arise only through a handful of
mechanisms, lending particular focus to Freeze-Out and Decay and Freeze-In, as
well as their variations involving late time re-annihilations of DM and DM
particle anti-particle asymmetries. Much like standard Freeze-Out, where the
abundance of DM depends only on the annihilation cross-section of the DM
particle, these mechanisms depend only on a very small subset of physical
parameters, many of which may be measured directly at the LHC. In particular,
we show that each DM production mechanism is associated with a distinctive
window in lifetimes and cross-sections for particles which may be produced in
the near future. We evaluate prospects for employing the LHC to definitively
reconstruct the origin of DM in a companion paper.Comment: 32 pages, 19 figures; v2: references added, published versio
A Geometry of the Generations
We propose a geometric theory of flavor based on the discrete group
, in the context of the minimal supersymmetric standard model. The
group treats three objects symmetrically, while making fundamental distinctions
between the generations. The top quark is the only heavy quark in the symmetry
limit, and the first and second generation squarks are degenerate. The
hierarchical nature of Yukawa matrices is a consequence of a sequential
breaking of .Comment: 10 pages, 1 EPS figure as uuencoded tar-compressed file, uses
psfig.st
Brief Report: Endothelial Progenitor Cell Phenotype and Function Are Impaired in ChildhoodâOnset Systemic Lupus Erythematosus
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/112288/1/art39149.pd
Hypercharge and the Cosmological Baryon Asymmetry
Stringent bounds on baryon and lepton number violating interactions have been
derived from the requirement that such interactions, together with electroweak
instantons, do not destroy a cosmological baryon asymmetry produced at an
extremely high temperature in the big bang. While these bounds apply in
specific models, we find that they are generically evaded. In particular, the
only requirement for a theory to avoid these bounds is that it contain charged
particles which, during a certain cosmological epoch, carry a non-zero
hypercharge asymmetry. Hypercharge neutrality of the universe then dictates
that the remaining particles must carry a compensating hypercharge density,
which is necessarily shared amongst them so as to give a baryon asymmetry.
Hence the generation of a hypercharge density in a sector of the theory forces
the universe to have a baryon asymmetry.Comment: 12 pages plus 1 Postscript figure available upon request. LBL 3482
Dose-Reduced Busulfan, Cyclophosphamide, and Autologous Stem Cell Transplantation for Human Immunodeficiency VirusâAssociated Lymphoma: AIDS Malignancy Consortium Study 020
AbstractIntensive chemotherapy for human immunodeficiency virus (HIV)-associated non-Hodgkin lymphoma (NHL) and Hodgkin lymphoma (HL) has resulted in durable remissions in a substantial proportion of patients. High-dose chemotherapy and autologous stem cell transplantation (AuSCT), moreover, has resulted in sustained complete remissions in selected patients with recurrent chemosensitive disease. Based on a favorable experience with dose-reduced high-dose busulfan, cyclophosphamide, and AuSCT for older patients with non-HIVâassociated aggressive lymphomas, an AIDS Malignancy Consortium multicenter trial was undertaken using the same dose-reduced busulfan and cyclophosphamide preparative regimen with AuSCT for recurrent HIV-associated NHL and HL. Of the 27 patients in the study, 20 received an AuSCT. The median time to achievement of an absolute neutrophil count (ANC) of â„ 0.5Ă109/L was 11 days (range, 9-16 days). The median time to achievement of an unsupported platelet count of â„ 20Ă109/L was 13 days (range, 6-57 days). One patient died on day +33 posttransplantation from hepatic veno-occlusive disease (VOD) and multiorgan failure. No other fatal regimen-related toxicity occurred. Ten of 19 patients (53%) were in complete remission at the time of their day +100 post-AuSCT evaluation. Of the 20 patients, 10 were alive and event-free at a median of 23 weeks post-AuSCT. Median overall survival (OS) was not reached by 13 of the 20 patients alive at the time of last follow-up. This multi-institutional trial demonstrates that a regimen of dose-reduced high-dose busulfan, cyclophosphamide, and AuSCT is well tolerated and is associated with favorable disease-free survival (DFS) and OS probabilities for selected patients with HIV-associated NHL and HL
Evidence for He I 10830 \AA~ absorption during the transit of a warm Neptune around the M-dwarf GJ 3470 with the Habitable-zone Planet Finder
Understanding the dynamics and kinematics of out-flowing atmospheres of hot
and warm exoplanets is crucial to understanding the origins and evolutionary
history of the exoplanets near the evaporation desert. Recently, ground based
measurements of the meta-stable Helium atom's resonant absorption at 10830
\AA~has become a powerful probe of the base environment which is driving the
outflow of exoplanet atmospheres. We report evidence for the He I 10830 \AA~in
absorption (equivalent width \AA) in the exosphere of
a warm Neptune orbiting the M-dwarf GJ 3470, during three transits using the
Habitable Zone Planet Finder (HPF) near infrared spectrograph. This marks the
first reported evidence for He I 10830 \AA\, atmospheric absorption for a
planet orbiting an M-dwarf. Our detected absorption is broad and its
blueshifted wing extends to -36 km/sec, the largest reported in the literature
to date. We modelled the state of Helium atoms in the exosphere of GJ3470b
based on assumptions on the UV and X-ray flux of GJ 3470, and found our
measurement of flux-weighted column density of meta-stable state Helium
, derived from our transit
observations, to be consistent with model, within its uncertainties. The
methodology developed here will be useful to study and constrain the
atmospheric outflow models of other exoplanets like GJ 3470b which are near the
edge of the evaporation desert.Comment: Accepted in Ap
Gauge Unification in Higher Dimensions
A complete 5-dimensional SU(5) unified theory is constructed which, on
compactification on the orbifold with two different Z_2's (Z_2 and Z_2'),
yields the minimal supersymmetric standard model. The orbifold accomplishes
SU(5) gauge symmetry breaking, doublet-triplet splitting, and a vanishing of
proton decay from operators of dimension 5. Until 4d supersymmetry is broken,
all proton decay from dimension 4 and dimension 5 operators is forced to vanish
by an exact U(1)_R symmetry. Quarks and leptons and their Yukawa interactions
are located at the Z_2 orbifold fixed points, where SU(5) is unbroken. A new
mechanism for introducing SU(5) breaking into the quark and lepton masses is
introduced, which originates from the SU(5) violation in the zero-mode
structure of bulk multiplets. Even though SU(5) is absent at the Z_2' orbifold
fixed point, the brane threshold corrections to gauge coupling unification are
argued to be negligibly small, while the logarithmic corrections are small and
in a direction which improves the agreement with the experimental measurements
of the gauge couplings. Furthermore, the X gauge boson mass is lowered, so that
proton decay to e^+ \pi^0 is expected with a rate within about one order of
magnitude of the current limit. Supersymmetry breaking occurs on the Z_2'
orbifold fixed point, and is felt directly by the gauge and Higgs sectors,
while squarks and sleptons acquire mass via gaugino mediation, solving the
supersymmetric flavor problem.Comment: 21 pages, Latex, references added, final versio
Manacled to Identity: Cosmopolitanism, Class, and âThe Culture Conceptâ in Stephen Crane
This article begins with a close reading of Stephen Craneâs short story âManacledâ from 1900, which situates this rarely considered short work within the context of contemporary debates about realism. I then proceed to argue that many of the debates raised by the tale have an afterlife in our own era of American literary studies, which has frequently focused on questions of âidentityâ and âcultureâ in its reading of realism and naturalism to the exclusion of the importance of cosmopolitan discourses of diffusion and exchange across national borders. I then offer a brief reading of Craneâs novel Georgeâs Mother, which follows Walter Benn Michaels in suggesting that the recent critical attention paid to particularities of cultural difference in American studies have come to conflate ideas of class and social position with ideas of culture in ways that have ultimately obscured the presence of genuine historical inequalities in US society. In order to challenge this critical commonplace, I situate Craneâs work within a history of transatlantic cosmopolitanism associated with the ideas of Franz Boas and Matthew Arnold to demonstrate the ways in which Craneâs narratives sought out an experience of the universal within their treatments of the particular
Impact of crosshatch patterns in H2RGs on high-precision radial velocity measurements: exploration of measurement and mitigation paths with the Habitable-Zone Planet Finder
Teledyneâs H2RG detector images suffer from crosshatch like patterns, which arise from subpixel quantum efficiency (QE) variation. We present our measurements of this subpixel QE variation in the Habitable-Zone Planet Finderâs H2RG detector. We present a simple model to estimate the impact of subpixel QE variations on the radial velocity and how a first-order correction can be implemented to correct for the artifact in the spectrum. We also present how the HPFâs future upgraded laser frequency comb will enable us to implement this correction
Small Numbers from Tunneling Between Brane Throats
Generic classes of string compactifications include ``brane throats''
emanating from the compact dimensions and separated by effective potential
barriers raised by the background gravitational fields. The interaction of
observers inside different throats occurs via tunnelling and is consequently
weak. This provides a new mechanism for generating small numbers in Nature. We
apply it to the hierarchy problem, where supersymmetry breaking near the
unification scale causes TeV sparticle masses inside the standard model throat.
We also design naturally long-lived cold dark matter which decays within a
Hubble time to the approximate conformal matter of a long throat. This may
soften structure formation at galactic scales and raises the possibility that
much of the dark matter of the universe is conformal matter. Finally, the
tunnelling rate shows that the coupling between throats, mediated by bulk
modes, is stronger than a naive application of holography suggests.Comment: 11 pages, 2 figures. Small corrections to match the published versio
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