372 research outputs found
Tri-bimaximal Neutrino Mixing from A(4) and \theta_{13} \sim \theta_C
It is a common believe that, if the Tri-bimaximal mixing (TBM) pattern is
explained by vacuum alignment in an A(4) model, only a very small reactor
angle, say \theta_{13} \sim \lambda^2_C being \lambda_C \equiv \theta_C the
Cabibbo angle, can be accommodated. This statement is based on the assumption
that all the flavon fields acquire VEVs at a very similar scale and the
departures from exact TBM arise at the same perturbation level. From the
experimental point of view, however, a relatively large value \theta_{13} \sim
\lambda_C is not yet excluded by present data. In this paper, we propose a
Seesaw A(4) model in which the previous assumption can naturally be evaded. The
aim is to describe a \theta_{13} \sim \lambda_C without conflicting with the
TBM prediction for \theta_{12} which is rather close to the observed value (at
\lambda^2_C level). In our model the deviation of the atmospherical angle from
maximal is subject to the sum-rule: \sin ^2 \theta_{23} \approx 1/2 +
\sqrt{2}/2 \sin \delta \cos \theta_{13} which is a next-to-leading order
prediction of our model.Comment: 16 pages, revised, typos corrected, references adde
Epidemiological determinants of spread of causal agent of severe acute respiratory syndrome in Hong Kong.
BACKGROUND: Health authorities worldwide, especially in the Asia Pacific region, are seeking effective public-health interventions in the continuing epidemic of severe acute respiratory syndrome (SARS). We assessed the epidemiology of SARS in Hong Kong. METHODS: We included 1425 cases reported up to April 28, 2003. An integrated database was constructed from several sources containing information on epidemiological, demographic, and clinical variables. We estimated the key epidemiological distributions: infection to onset, onset to admission, admission to death, and admission to discharge. We measured associations between the estimated case fatality rate and patients' age and the time from onset to admission. FINDINGS: After the initial phase of exponential growth, the rate of confirmed cases fell to less than 20 per day by April 28. Public-health interventions included encouragement to report to hospital rapidly after the onset of clinical symptoms, contact tracing for confirmed and suspected cases, and quarantining, monitoring, and restricting the travel of contacts. The mean incubation period of the disease is estimated to be 6.4 days (95% CI 5.2-7.7). The mean time from onset of clinical symptoms to admission to hospital varied between 3 and 5 days, with longer times earlier in the epidemic. The estimated case fatality rate was 13.2% (9.8-16.8) for patients younger than 60 years and 43.3% (35.2-52.4) for patients aged 60 years or older assuming a parametric gamma distribution. A non-parametric method yielded estimates of 6.8% (4.0-9.6) and 55.0% (45.3-64.7), respectively. Case clusters have played an important part in the course of the epidemic. INTERPRETATION: Patients' age was strongly associated with outcome. The time between onset of symptoms and admission to hospital did not alter outcome, but shorter intervals will be important to the wider population by restricting the infectious period before patients are placed in quarantine
Transmission dynamics of the etiological agent of SARS in Hong Kong: impact of public health interventions.
We present an analysis of the first 10 weeks of the severe acute respiratory syndrome (SARS) epidemic in Hong Kong. The epidemic to date has been characterized by two large clusters-initiated by two separate "super-spread" events (SSEs)-and by ongoing community transmission. By fitting a stochastic model to data on 1512 cases, including these clusters, we show that the etiological agent of SARS is moderately transmissible. Excluding SSEs, we estimate that 2.7 secondary infections were generated per case on average at the start of the epidemic, with a substantial contribution from hospital transmission. Transmission rates fell during the epidemic, primarily as a result of reductions in population contact rates and improved hospital infection control, but also because of more rapid hospital attendance by symptomatic individuals. As a result, the epidemic is now in decline, although continued vigilance is necessary for this to be maintained. Restrictions on longer range population movement are shown to be a potentially useful additional control measure in some contexts. We estimate that most currently infected persons are now hospitalized, which highlights the importance of control of nosocomial transmission
Fermion Mass Hierarchies and Flavour Mixing from a Minimal Discrete Symmetry
We construct a simple model of fermion masses based on a spontaneously broken
S3 X Z3 flavour group. At the leading order, in the neutrino sector S3 is
broken down to a \nu_\mu-\nu_\tau parity subgroup that enforces a maximal
atmospheric mixing angle and a vanishing \theta_{13}. In the charged lepton
sector the \nu_\mu-\nu_\tau parity is maximally broken and the resulting mass
matrix is nearly diagonal. The charged lepton mass hierarchy is automatically
reproduced by the S3 symmetry breaking parameter alone. A careful analysis
shows that, after the inclusion of all relevant subleading effects, the model
predicts \theta_{23}=\pi/4+O(\lambda_c^2) and \theta_{13}=O(\lambda_c^2),
\lambda_c denoting the Cabibbo angle. A simple extension to the quark sector is
also illustrated, where the mass spectrum and the mixing angles are naturally
reproduced, with the exception of the mixing angle between the first two
generations, that requires a small accidental enhancement.Comment: 18 page
Lepton Flavour Violation in a Supersymmetric Model with A4 Flavour Symmetry
We compute the branching ratios for mu-> e gamma, tau-> mu gamma and tau -> e
gamma in a supersymmetric model invariant under the flavour symmetry group A4 X
Z3 X U(1)_{FN}, in which near tri-bimaximal lepton mixing is naturally
predicted. At leading order in the small symmetry breaking parameter u, which
is of the same order as the reactor mixing angle theta_{13}, we find that the
branching ratios generically scale as u^2. Applying the current bound on the
branching ratio of mu -> e gamma shows that small values of u or tan(beta) are
preferred in the model for mass parameters m_{SUSY} and m_{1/2} smaller than
1000 GeV. The bound expected from the on-going MEG experiment will provide a
severe constraint on the parameter space of the model either enforcing u approx
0.01 and small tan(beta) or m_{SUSY} and m_{1/2} above 1000 GeV. In the special
case of universal soft supersymmetry breaking terms in the flavon sector a
cancellation takes place in the amplitudes and the branching ratios scale as
u^4, allowing for smaller slepton masses. The branching ratios for tau -> mu
gamma and tau -> e gamma are predicted to be of the same order as the one for
mu -> e gamma, which precludes the possibility of observing these tau decays in
the near future.Comment: 44 page
Fermion Masses and Mixings in a S4 Based Model
It has been recently claimed that the symmetry group S4 yields to the
Tri-bimaximal neutrino mixing in a "natural" way from the group theory point of
view. Approving of this feature as an indication, we build a supersymmetric
model of lepton and quark masses based on this family symmetry group. In the
lepton sector, a correct mass hierarchy among the charged leptons is achieved
together to a neutrino mass matrix which can be diagonalized by the
Tri-bimaximal pattern. Our model results to be phenomenologically unequivalent
with respect to other proposals based on different flavour groups but still
predicting the Tri-bimaximal mixing. In the quark sector a realistic pattern
for masses and mixing angles is obtained. The flavour structures of the mass
matrices in both the sectors come from the spontaneously symmetry breaking of
S4, due to several scalar fields, which get non-zero vacuum expectation values.
A specific vacuum alignment is required and it is shown to be a natural results
of the minimization of the scalar potential and, moreover, to be stable under
the corrections from the higher order terms.Comment: 25 pages, LaTeX; added references and minor correctio
Chronic adiponectin deficiency leads to Alzheimer’s disease-like cognitive impairments and pathologies through AMPK inactivation and cerebral insulin resistance in aged mice
(a) Immunoblotting analysis of IRβ in the hippocampus and frontal cortex of 18-month old wildtype and APN-KO mice. (b) Densitometric analysis of the ratio of IRβ. Mean ± S.E.M.; ***p < 0.001, n.s. statistically not significant; Scale bar: 100 μm. (JPG 30 kb
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