32,686 research outputs found
Discussion on a possible neutrino detector located in India
We have identified some important and worthwhile physics opportunitites with
a possible neutrino detector located in India. Particular emphasis is placed on
the geographical advantage with a stress on the complimentary aspects with
respect to other neutrino detectors already in operation.Comment: 9 pages; arXiv copy of published proceedings contributio
Which solar neutrino experiment after KamLAND and Borexino?
We estimate how well we will know the parameters of solar neutrino
oscillations after KamLAND and Borexino. The expected error on Delta m^2 is few
per-mille in the VO and QVO regions, few per-cent in the LMA region, and around
10% in the LOW region. The expected error on sin^2 2theta is around 5%. KamLAND
and Borexino will tell unambiguously which specific new measurement, dedicated
to pp solar neutrinos, is able to contribute to the determination of theta and
perhaps of Delta m^2. The present data suggest as more likely outcomes: no
measurement, or the total pp rate, or its day/night variation.Comment: 12 pages, 4 figures. v2: comments and references added, final versio
Mass Hierarchy Determination via future Atmospheric Neutrino Detectors
We study the problem of determination of the sign of Delta m^2_{31}, or the
neutrino mass hierarchy, through observations of atmospheric neutrinos in
future detectors. We consider two proposed detector types :
(a) Megaton sized water Cerenkov detectors, which can measure the survival
rates of nu_\mu + \bar{\nu}_\mu and nu_e + \bar{\nu}_e and (b) 100 kton sized
magnetized iron detectors, which can measure the survival rates of \nu_\mu and
\bar{\nu}_\mu. For energies and path-lengths relevant to atmospheric neutrinos,
these rates obtain significant matter contributions from P_{\mu e}, P_{\mu \mu}
and P_{ee}, leading to an appreciable sensitivity to the hierarchy. We do a
binned \chi^2 analysis of simulated data in these two types of detectors which
includes the effect of smearing in neutrino energy and direction and
incorporates detector efficiencies and relevant statistical, theoretical and
systematic errors. We also marginalize the \chi^2 over the allowed ranges of
neutrino parameters in order to accurately account for their uncertainties.
Finally, we compare the performance of both types of detectors vis a vis the
hierarchy determination.Comment: 36 pages, 13 figures, revised version accepted in Physical Review
Lost in spatial translation - A novel tool to objectively assess spatial disorientation in Alzheimer's disease and frontotemporal dementia
Spatial disorientation is a prominent feature of early Alzheimer's disease (AD) attributed to degeneration of medial temporal and parietal brain regions, including the retrosplenial cortex (RSC). By contrast, frontotemporal dementia (FTD) syndromes show generally intact spatial orientation at presentation. However, currently no clinical tasks are routinely administered to objectively assess spatial orientation in these neurodegenerative conditions. In this study we investigated spatial orientation in 58 dementia patients and 23 healthy controls using a novel virtual supermarket task as well as voxel-based morphometry (VBM). We compared performance on this task with visual and verbal memory function, which has traditionally been used to discriminate between AD and FTD. Participants viewed a series of videos from a first person perspective travelling through a virtual supermarket and were required to maintain orientation to a starting location. Analyses revealed significantly impaired spatial orientation in AD, compared to FTD patient groups. Spatial orientation performance was found to discriminate AD and FTD patient groups to a very high degree at presentation. More importantly, integrity of the RSC was identified as a key neural correlate of orientation performance. These findings confirm the notion that i) it is feasible to assess spatial orientation objectively via our novel Supermarket task; ii) impaired orientation is a prominent feature that can be applied clinically to discriminate between AD and FTD and iii) the RSC emerges as a critical biomarker to assess spatial orientation deficits in these neurodegenerative conditions
Non-Abelian Dark Sectors and Their Collider Signatures
Motivated by the recent proliferation of observed astrophysical anomalies,
Arkani-Hamed et al. have proposed a model in which dark matter is charged under
a non-abelian "dark" gauge symmetry that is broken at ~ 1 GeV. In this paper,
we present a survey of concrete models realizing such a scenario, followed by a
largely model-independent study of collider phenomenology relevant to the
Tevatron and the LHC. We address some model building issues that are easily
surmounted to accommodate the astrophysics. While SUSY is not necessary, we
argue that it is theoretically well-motivated because the GeV scale is
automatically generated. Specifically, we propose a novel mechanism by which
mixed D-terms in the dark sector induce either SUSY breaking or a super-Higgs
mechanism precisely at a GeV. Furthermore, we elaborate on the original
proposal of Arkani-Hamed et al. in which the dark matter acts as a messenger of
gauge mediation to the dark sector. In our collider analysis we present
cross-sections for dominant production channels and lifetime estimates for
primary decay modes. We find that dark gauge bosons can be produced at the
Tevatron and the LHC, either through a process analogous to prompt photon
production or through a rare Z decay channel. Dark gauge bosons will decay back
to the SM via "lepton jets" which typically contain >2 and as many as 8
leptons, significantly improving their discovery potential. Since SUSY decays
from the MSSM will eventually cascade down to these lepton jets, the discovery
potential for direct electroweak-ino production may also be improved.
Exploiting the unique kinematics, we find that it is possible to reconstruct
the mass of the MSSM LSP. We also present decay channels with displaced
vertices and multiple leptons with partially correlated impact parameters.Comment: 44 pages, 25 figures, version published in JHE
- …