1,322 research outputs found
Dark Matter, Muon g-2 and Other SUSY Constraints
Recent developments constraining the SUSY parameter space are reviewed within
the framework of SUGRA GUT models. The WMAP data is seen to reduce the error in
the density of cold dark matter by about a factor of four, implying that the
lightest stau is only 5 -10 GeV heavier than the lightest neutralino when m_0,
m_{1/2} < 1 TeV. The CMD-2 re-analysis of their data has reduced the
disagreement between the Standard Model prediction and the Brookhaven
measurement of the muon magnetic moment to 1.9 sigma, while using the tau decay
data plus CVC, the disagreement is 0.7 sigma. (However, the two sets of data
remain inconsistent at the 2.9 sigma level.) The recent Belle and BABAR
measurements of the B -> phi K CP violating parameters and branching ratios are
discussed. They are analyzed theoretically within the BBNS improved
factorization method. The CP parameters are in disagreement with the Standard
Model at the 2.7 sigma level, and the branching ratios are low by a factor of
two or more over most of the parameter space. It is shown that both anomalies
can naturally be accounted for by adding a non-universal cubic soft breaking
term at M_G mixing the second and third generations.Comment: 16 pages, 7 figures, plenary talk at Beyond The Desert '03, Castle
Ringberg, Germany, June 9, 2003. Typos correcte
Bino Dark Matter and Big Bang Nucleosynthesis in the Constrained E6SSM with Massless Inert Singlinos
We discuss a new variant of the E6 inspired supersymmetric standard model
(E6SSM) in which the two inert singlinos are exactly massless and the dark
matter candidate has a dominant bino component. A successful relic density is
achieved via a novel mechanism in which the bino scatters inelastically into
heavier inert Higgsinos during the time of thermal freeze-out. The two massless
inert singlinos contribute to the effective number of neutrino species at the
time of Big Bang Nucleosynthesis, where the precise contribution depends on the
mass of the Z' which keeps them in equilibrium. For example for mZ' > 1300 GeV
we find Neff \approx 3.2, where the smallness of the additional contribution is
due to entropy dilution. We study a few benchmark points in the constrained
E6SSM with massless inert singlinos to illustrate this new scenario.Comment: 24 pages, revised for publication in JHE
Electrical detection of 31P spin quantum states
In recent years, a variety of solid-state qubits has been realized, including
quantum dots, superconducting tunnel junctions and point defects. Due to its
potential compatibility with existing microelectronics, the proposal by Kane
based on phosphorus donors in Si has also been pursued intensively. A key issue
of this concept is the readout of the P quantum state. While electrical
measurements of magnetic resonance have been performed on single spins, the
statistical nature of these experiments based on random telegraph noise
measurements has impeded the readout of single spin states. In this letter, we
demonstrate the measurement of the spin state of P donor electrons in silicon
and the observation of Rabi flops by purely electric means, accomplished by
coherent manipulation of spin-dependent charge carrier recombination between
the P donor and paramagnetic localized states at the Si/SiO2 interface via
pulsed electrically detected magnetic resonance. The electron spin information
is shown to be coupled through the hyperfine interaction with the P nucleus,
which demonstrates the feasibility of a recombination-based readout of nuclear
spins
Probing EWSB Naturalness in Unified SUSY Models with Dark Matter
We have studied Electroweak Symmetry Breaking (EWSB) fine-tuning in the
context of two unified Supersymmetry scenarios: the Constrained Minimal
Supersymmetric Model (CMSSM) and models with Non-Universal Higgs Masses (NUHM),
in light of current and upcoming direct detection dark matter experiments. We
consider both those models that satisfy a one-sided bound on the relic density
of neutralinos, , and also the subset that satisfy
the two-sided bound in which the relic density is within the 2 sigma best fit
of WMAP7 + BAO + H0 data. We find that current direct detection searches for
dark matter probe the least fine-tuned regions of parameter-space, or
equivalently those of lowest Higgs mass parameter , and will tend to probe
progressively more and more fine-tuned models, though the trend is more
pronounced in the CMSSM than in the NUHM. Additionally, we examine several
subsets of model points, categorized by common mass hierarchies; M_{\chi_0}
\sim M_{\chi^\pm}, M_{\chi_0} \sim M_{\stau}, M_{\chi_0} \sim M_{\stop_1}, the
light and heavy Higgs poles, and any additional models classified as "other";
the relevance of these mass hierarchies is their connection to the preferred
neutralino annihilation channel that determines the relic abundance. For each
of these subsets of models we investigated the degree of fine-tuning and
discoverability in current and next generation direct detection experiments.Comment: 26 pages, 10 figures. v2: references added. v3: matches published
versio
Challenges of Profile Likelihood Evaluation in Multi-Dimensional SUSY Scans
Statistical inference of the fundamental parameters of supersymmetric
theories is a challenging and active endeavor. Several sophisticated algorithms
have been employed to this end. While Markov-Chain Monte Carlo (MCMC) and
nested sampling techniques are geared towards Bayesian inference, they have
also been used to estimate frequentist confidence intervals based on the
profile likelihood ratio. We investigate the performance and appropriate
configuration of MultiNest, a nested sampling based algorithm, when used for
profile likelihood-based analyses both on toy models and on the parameter space
of the Constrained MSSM. We find that while the standard configuration is
appropriate for an accurate reconstruction of the Bayesian posterior, the
profile likelihood is poorly approximated. We identify a more appropriate
MultiNest configuration for profile likelihood analyses, which gives an
excellent exploration of the profile likelihood (albeit at a larger
computational cost), including the identification of the global maximum
likelihood value. We conclude that with the appropriate configuration MultiNest
is a suitable tool for profile likelihood studies, indicating previous claims
to the contrary are not well founded.Comment: 21 pages, 9 figures, 1 table; minor changes following referee report.
Matches version accepted by JHE
A robust, scanning quantum system for nanoscale sensing and imaging
Controllable atomic-scale quantum systems hold great potential as sensitive
tools for nanoscale imaging and metrology. Possible applications range from
nanoscale electric and magnetic field sensing to single photon microscopy,
quantum information processing, and bioimaging. At the heart of such schemes is
the ability to scan and accurately position a robust sensor within a few
nanometers of a sample of interest, while preserving the sensor's quantum
coherence and readout fidelity. These combined requirements remain a challenge
for all existing approaches that rely on direct grafting of individual solid
state quantum systems or single molecules onto scanning-probe tips. Here, we
demonstrate the fabrication and room temperature operation of a robust and
isolated atomic-scale quantum sensor for scanning probe microscopy.
Specifically, we employ a high-purity, single-crystalline diamond nanopillar
probe containing a single Nitrogen-Vacancy (NV) color center. We illustrate the
versatility and performance of our scanning NV sensor by conducting
quantitative nanoscale magnetic field imaging and near-field single-photon
fluorescence quenching microscopy. In both cases, we obtain imaging resolution
in the range of 20 nm and sensitivity unprecedented in scanning quantum probe
microscopy
Double quantum dot with integrated charge sensor based on Ge/Si heterostructure nanowires
Coupled electron spins in semiconductor double quantum dots hold promise as
the basis for solid-state qubits. To date, most experiments have used III-V
materials, in which coherence is limited by hyperfine interactions. Ge/Si
heterostructure nanowires seem ideally suited to overcome this limitation: the
predominance of spin-zero nuclei suppresses the hyperfine interaction and
chemical synthesis creates a clean and defect-free system with highly
controllable properties. Here we present a top gate-defined double quantum dot
based on Ge/Si heterostructure nanowires with fully tunable coupling between
the dots and to the leads. We also demonstrate a novel approach to charge
sensing in a one-dimensional nanostructure by capacitively coupling the double
dot to a single dot on an adjacent nanowire. The double quantum dot and
integrated charge sensor serve as an essential building block required to form
a solid-state spin qubit free of nuclear spin.Comment: Related work at http://marcuslab.harvard.edu and
http://cmliris.harvard.ed
Scanning-probe spectroscopy of semiconductor donor molecules
Semiconductor devices continue to press into the nanoscale regime, and new
applications have emerged for which the quantum properties of dopant atoms act
as the functional part of the device, underscoring the necessity to probe the
quantum structure of small numbers of dopant atoms in semiconductors[1-3].
Although dopant properties are well-understood with respect to bulk
semiconductors, new questions arise in nanosystems. For example, the quantum
energy levels of dopants will be affected by the proximity of nanometer-scale
electrodes. Moreover, because shallow donors and acceptors are analogous to
hydrogen atoms, experiments on small numbers of dopants have the potential to
be a testing ground for fundamental questions of atomic and molecular physics,
such as the maximum negative ionization of a molecule with a given number of
positive ions[4,5]. Electron tunneling spectroscopy through isolated dopants
has been observed in transport studies[6,7]. In addition, Geim and coworkers
identified resonances due to two closely spaced donors, effectively forming
donor molecules[8]. Here we present capacitance spectroscopy measurements of
silicon donors in a gallium-arsenide heterostructure using a scanning probe
technique[9,10]. In contrast to the work of Geim et al., our data show
discernible peaks attributed to successive electrons entering the molecules.
Hence this work represents the first addition spectrum measurement of dopant
molecules. More generally, to the best of our knowledge, this study is the
first example of single-electron capacitance spectroscopy performed directly
with a scanning probe tip[9].Comment: In press, Nature Physics. Original manuscript posted here; 16 pages,
3 figures, 5 supplementary figure
Naturalness and Fine Tuning in the NMSSM: Implications of Early LHC Results
We study the fine tuning in the parameter space of the semi-constrained
NMSSM, where most soft Susy breaking parameters are universal at the GUT scale.
We discuss the dependence of the fine tuning on the soft Susy breaking
parameters M_1/2 and m0, and on the Higgs masses in NMSSM specific scenarios
involving large singlet-doublet Higgs mixing or dominant Higgs-to-Higgs decays.
Whereas these latter scenarios allow a priori for considerably less fine tuning
than the constrained MSSM, the early LHC results rule out a large part of the
parameter space of the semi-constrained NMSSM corresponding to low values of
the fine tuning.Comment: 19 pages, 10 figures, bounds from Susy searches with ~1/fb include
Supersymmetric Monojets at the Large Hadron Collider
Supersymmetric monojets may be produced at the Large Hadron Collider by the
process qg -> squark neutralino_1 -> q neutralino_1 neutralino_1, leading to a
jet recoiling against missing transverse momentum. We discuss the feasibility
and utility of the supersymmetric monojet signal. In particular, we examine the
possible precision with which one can ascertain the neutralino_1-squark-quark
coupling via the rate for monojet events. Such a coupling contains information
on the composition of the neutralino_1 and helps bound dark matter direct
detection cross-sections and the dark matter relic density of the neutralino_1.
It also provides a check of the supersymmetric relation between gauge couplings
and gaugino-quark-squark couplings.Comment: 46 pages, 10 figures. The appendix has been rewritten to correct an
error that appears in all previous versions of the appendix. This error has
no effect on the results in the main body of the pape
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