5,958 research outputs found
estimate and bounds on nonstandard interactions at source and detector in the solar neutrino low-energy regime
We explore the implications of the Borexino experiment's real time
measurements of the lowest energy part of the neutrino spectrum from the
primary pp fusion process up to 0.420 MeV through the 7^Be decay at 0.862 MeV
to the pep reaction at 1.44 MeV. We exploit the fact that at such low energies,
the large mixing angle solution to the Mikheyev-Smirnov-Wolfenstein matter
effects in the sun are small for 7^Be and pep and negligible for pp.
Consequently, the neutrinos produced in the sun change their flavor almost
entirely through vacuum oscillations during propagation from the sun's surface
and through possible nonstandard interactions acting at the solar source and
Borexino detector. We combine the different NSI effects at source and detector
in a single framework and use the current Borexino data to bound NSI
non-universal and flavor- changing parameters at energies below the reach of
reactor neutrino experiments. We also study the implication of the current data
for the weak- mixing angle at this "low-energy frontier" data from the Borexino
experiment, where it is expected to be slightly larger than its value at the Z
mass. We find , the lowest energy-scale estimate
to date. Looking to the future, we use projected sensitivities to solar
neutrinos in next generation dedicated solar experiments and direct dark matter
detection experiments and find a potential factor five improvement in
determination of the weak-mixing angle and up to an order of magnitude
improvement in probing the NSI parameters space.Comment: 20 pages, 09 figures, lowest-energy value of sin^2(theta)w to date
has been reported. Some text added. New sub-section(7.5) added. Published in
JHE
On the Exceptional Gauged WZW Theories
We consider two different versions of gauged WZW theories with the
exceptional groups and gauged with any of theirs null subgroups. By
constructing suitable automorphism, we establish the equivalence of these two
theories. On the other hand our automorphism, relates the two dual irreducible
Riemannian globally symmetric spaces with different characters based on the
corresponding exceptional Lie groups.Comment: 5 pages, LaTeX fil
Time-Consistent No-Arbitrage Models of the Term Structure
We present an econometric procedure for calibrating no-arbitrage term structure models in a way that is time-consistent and robust to measurement errors. Typical no-arbitrage models are time-inconsistent because their parameters are assumed constant for pricing purposes despite the fact that the parameters change whenever the model is recalibrated. No-arbitrage models are also sensitive to measurement errors because they fit exactly each potentially contaminated bond price in the cross-section. We overcome both problems by evaluating bond prices using the joint dynamics of the factors and calibrated parameters and by locally averaging out the measurement errors. Our empirical application illustrates the trade-off between fitting as well as possible and overfitting the cross-section of bond prices due to measurement errors. After optimizing this trade-off, our approach fits almost exactly the cross-section of bond prices at each date and produces out-of-sample forecast errors that beat a random walk benchmark and are comparable to the results in the affine term structure literature. We find that non-linearities in the pricing kernel are important, lending support to quadratic term structure models.
Localization, anomalous diffusion and slow relaxations: a random distance matrix approach
We study the spectral properties of a class of random matrices where the
matrix elements depend exponentially on the distance between uniformly and
randomly distributed points. This model arises naturally in various physical
contexts, such as the diffusion of particles, slow relaxations in glasses, and
scalar phonon localization. Using a combination of a renormalization group
procedure and a direct moment calculation, we find the eigenvalue distribution
density (i.e., the spectrum) and the localization properties of the eigenmodes,
for arbitrary dimension. Finally, we discuss the physical implications of the
results
Transient Emission From Dissipative Fronts in Magnetized, Relativistic Outflows. II. Synchrotron Flares
The time dependent synchrotron emission from relativistic jets, and the
relation between the synchrotron and ERC emission is considered within the
framework of the radiative front model. The timescale and profile of the
optically thin emission are shown to be determined, in this model, by the shock
formation radius, the thickness of expelled fluid slab and the variation of the
front's parameters due to its transverse expansion. For a range of reasonable
conditions, a variety of flare shapes can be produced, varying from roughly
symmetric with exponential rises and decays, as often seen in blazars, to
highly asymmetric with a fast rise and a much slower, power law decay, as seen
in GRB afterglows. The onset, duration, and fluence of low-frequency (below the
initial turnover frequency) and hard gamma-ray (above the initial gamma-spheric
energy) outbursts are limited by opacity effects; the emission at these
energies is quite generally delayed and, in the case of sufficiently short
length outbursts, severely attenuated. The observational consequences are
discussed. One distinctive prediction of this model is that in a single,
powerful source, the upper cutoff of the gamma-ray spectrum should be
correlated with the timescale of the outburst and with the amplitude of
variations at long wavelengths (typically radio to millimeter).Comment: AAS LaTex, 14 pgs, accepted to A
Quantum dynamics in a tiered non-Markovian environment
We introduce a new analytical method for studying the open quantum systems
problem of a discrete system weakly coupled to an environment of harmonic
oscillators. Our approach is based on a phase space representation of the
density matrix for a system coupled to a two-tiered environment. The dynamics
of the system and its immediate environment are resolved in a non-Markovian
way, and the environmental modes of the inner environment can themselves be
damped by a wider `universe'. Applying our approach to the canonical cases of
the Rabi and spin-boson models we obtain new analytical expressions for an
effective thermalisation temperature and corrections to the environmental
response functions as direct consequences of considering such a tiered
environment. A comparison with exact numerical simulations confirms that our
approximate expressions are remarkably accurate, while their analytic nature
offers the prospect of deeper understanding of the physics which they describe.
A unique advantage of our method is that it permits the simultaneous inclusion
of a continuous bath as well as discrete environmental modes, leading to wide
and versatile applicability.Comment: Video abstract available at
http://iopscience.iop.org/1367-2630/17/2/023063. 15 pages, 6 figure
Systemic Risk and the Refinancing Ratchet Effect
The confluence of three trends in the U.S. residential housing market-rising home prices, declining interest rates, and near-frictionless refinancing opportunities-led to vastly increased systemic risk in the financial system. Individually, each of these trends is benign, but when they occur simultaneously, as they did over the past decade, they impose an unintentional synchronization of homeowner leverage. This synchronization, coupled with the indivisibility of residential real estate that prevents homeowners from deleveraging when property values decline and homeowner equity deteriorates, conspire to create a "ratchet" effect in which homeowner leverage is maintained during good times without the ability to decrease leverage during bad times. If refinancing-facilitated homeowner-equity extraction is sufficiently widespread-as it was during the years leading up to the peak of the U.S. residential real-estate market-the inadvertent coordination of leverage during a market rise implies higher correlation of defaults during a market drop. To measure the systemic impact of this ratchet effect, we simulate the U.S. housing market with and without equity extractions, and estimate the losses absorbed by mortgage lenders by valuing the embedded put-option in non-recourse mortgages. Our simulations generate loss estimates of 280 billion in the absence of equity extractions.Risk; Financial Crisis; Household Finance; Real Estate; Subprime
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