318 research outputs found
Photogenetic Retinal Prosthesis
The last few decades have witnessed an immense effort to develop working retinal implants for patients suffering from retinal degeneration diseases such as retinitis pigmentosa. However, it is becoming apparent that this approach is unable to restore levels of vision that will be sufficient to offer significant improvement in the quality of life of patients. Herein, a new type of retinal prosthesis that is based on genetic expression of microbial light sensitive ion channel, Chanelrhodopsin-2 (ChR2), and a remote light stimulation is examined. First, the dynamics of the ChR2 stimulation is characterized and it is shown that (1) the temporal resolution of ChR2-evoked spiking is limited by a continuous drop in its depolarization efficiency that is due to (a) frequency-independent desensitization process and (b) slow photocurrent shutting, which leads to a frequency-dependent post-spike depolarization and (2) the ChR2 response to light can be accurately reproduced by a four-state model consisting of two interconnected branches of open and close states. Then, a stimulation prototype is developed and its functionality is demonstrated in-vitro. The prototype uses a new micro-emissive matrix which enables generating of two-dimensional stimulation patterns with enhanced resolution compared to the conventional retinal implants. Finally, based on the micro-emitters matrix, a new technique for sub-cellular and network-level neuroscience experimentations is shown. The capacity to excite sub-cellular compartments is demonstrated and an example utility to fast map variability in dendrites conductance is shown. The outcomes of this thesis present an outline and a first proof-of-concept for a future photogenetic retinal prosthesis. In addition, they provide the emerging optogenetic technology with a detailed analysis of its temporal resolution and a tool to expand its spatial resolution, which can have immediate high impact applications in modulating the activity of sub-cellular compartments, mapping neuronal networks and studying synchrony and plasticity effects
Future prospects of B physics
In recent years, the CKM picture of flavor and CP violation has been
confirmed, mainly due to B decay data. Yet, it is likely that there are small
corrections to this picture. We expect to find new physics not much above the
weak scale. This new physics could modify flavor changing processes compared to
their SM expectations. Much larger B decay data sets, which are expected from
LHCb and super--factories, will be used to search for these deviations with
much improved sensitivity. The combination of low and high energy data will be
particularly useful to probe the structure of new physics.Comment: 19 pages. To appear in the Progress of Theoretical Physics special
issue commemorating Kobayashi and Maskawa Nobel prize. v2: references added.
Final version to appear in the journa
A Model Independent Construction of the Unitarity Triangle
In a large class of models, the only significant new physics effect on the CP
asymmetries in and decays is a new contribution
to the mixing amplitude. This allows a model independent
construction of the CKM Unitarity Triangle (up to hadronic uncertainties).
Furthermore, the contributions to the mixing from the Standard Model and from
the new physics can be disentangled. A serious obstacle to this analysis is an
eightfold discrete ambiguity in solving for the angles of the triangle. Several
ways to reduce the ambiguity either by making further measurements, or by
making further assumptions about the nature of the new physics are described.Comment: 14 pages, harvmac, 2 figures uses eps
CP Violation Beyond the Standard Model
We review CP violation in various extensions of the electroweak sector of the
Standard Model. A particular emphasis is put on supersymmetric models. We
describe the two CP problems of supersymmetry, concerning and
. We critically review the various mechanisms that have been
suggested to solve these problems: exact universality, approximate CP symmetry,
alignment, approximate universality and heavy squarks. We explain how future
measurements of CP violation will test these mechanisms. We describe extensions
of the quark sector and their implications on CP asymmetries in neutral B
decays, on the decay and on . We
discuss CP violation in charged scalar exchange in models with natural flavor
conservation and explain how transverse lepton polarization in meson decays can
probe such models. CP violation in neutral scalar exchange arises in models of
horizontal symmetries and may be manifest in heavy quark (b and t) physics. We
describe the implications of Left-Right Symmetric models on ,
, and CP asymmetries in B decays. Finally, we
briefly discuss the potential of future measurements of CP violation to
discover New Physics.Comment: 50 pages, harvmac, 1 figure. To appear in the Review Volume "Heavy
Flavours II", eds. A.J. Buras and M. Lindner, Advanced Series on Directions
in High Energy Physics, World Scientific Publishing Co., Singapor
and leptonic decays as probes of solutions to the puzzle
Experimental measurements of the ratios () show a
deviation from the Standard Model prediction. In the absence of
light right-handed neutrinos, a new physics contribution to
decays necessarily modifies also and/or transitions. These contributions lead to violation of lepton
flavor universality in, respectively, and leptonic decays. We
analyze the constraints resulting from measurements of the leptonic
vector-meson decays on solutions to the puzzle. Available data
from BaBar and Belle can already disfavor some of the new physics explanations
of this anomaly. Further discrimination can be made by measuring
in the upcoming Belle II experiment.Comment: Version published in JHEP, 17 pages, 7 figure
The Role of CP violation in D0 anti-D0 Mixing
In current searches for D0 anti-D0 mixing, the time evolution of
``wrong-sign'' decays is used to distinguish between a potential mixing signal
and the dominant background from doubly-Cabibbo-suppressed decays. A term
proportional to in the expression for the time evolution is often
neglected in theoretical discussions and experimental analyses of these
processes. We emphasize that, in general, this term does not vanish even in the
case of CP invariance. Furthermore, CP invariance is likely to be violated if
the rate of D0 anti-D0 mixing is close to the experimental bound. The
consequence of either of these two facts is that the strongest existing
measured bound is not applicable for constraining New Physics.Comment: 14 pages, uuencoded gzip-compressed postscript (84 kB
Implications of the Fleischer-Mannel Bound
Fleischer and Mannel (FM) have shown that it may become possible to constrain
the angle of the unitarity triangle from measurements of various
decays. This constraint is independent of hadronic uncertainties to
the few percent level. We show that, within the Standard Model, the FM bound
gives strong constraints on the CKM parameters. In particular, it could predict
a well defined sign for and . In a class of
extensions of the Standard Model, where the New Physics affects only (and, in particular, not ) processes, the FM bound can lead to
constraints on CP asymmetries in decays into final CP eigenstates even if
mixing is dominated by unknown New Physics. In our analysis, we use
a new method to combine in a statistically meaningful way the various
measurements that involve CKM parameters.Comment: 24 pages, revtex, 6 figures included using psfi
New Physics and Future B Factories
Further experimental and theoretical studies of the physics of flavor and CP
violation are well motivated. Within the supersymmetric framework, higher
precision measurements will allow to explore classes of models with stronger
degree of universality: first, models with no universality, such as alignment
or heavy first two squark generations; second, models with approximate
universality, such as dilaton dominance or AMSB; and finally models of exact
universality, such as GMSB. A broad program, including various rare processes
or CP asymmetries in B, D and K decays, will provide detailed information about
viable extensions of the Standard Model. Some highlights of future B-physics
experiments (the present B-factories with integrated luminosity of 0.5 ab^{-1},
hadron machines, and future high-luminosity B-factories) are described.Comment: 16 pages; An extended version of the contribution to the proceedings
of the fifth KEK topical conference `Frontiers in Flavor Physics', KEK,
Tsukuba, Japan, November 2001; Talk at the conference given by Y
The importance of N2 leptogenesis
We argue that fast interactions of the lightest singlet neutrino would
project part of a preexisting lepton asymmetry onto a direction that is
protected from washout effects, thus preventing it from being erased. In
particular, we consider an asymmetry generated in decays, assuming that
interactions are fast enough to bring into full thermal
equilibrium. If decays occur at T\gsim 10^9 GeV, that is, before the
muon Yukawa interactions enter into thermal equilibrium, then generically part
of survives. In this case some of the constraints implied by the standard
leptogenesis scenario hold only if . For T\lsim 10^9
GeV, is generally erased, unless special alignment/orthogonality
conditions in flavor space are realized.Comment: 5 pages. A few clarifications added, conclusions unchanged. Version
published in Phys. Rev. Lett. (Title changed in journal
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