3,203 research outputs found
The Effective in Matter
In this paper we generalize the concept of an effective for
disappearance experiments, which has been extensively used
by the short baseline reactor experiments, to include the effects of
propagation through matter for longer baseline
disappearance experiments. This generalization is a trivial, linear combination
of the neutrino mass squared eigenvalues in matter and thus is not a simple
extension of the usually vacuum expression, although, as it must, it reduces to
the correct expression in the vacuum limit. We also demonstrated that the
effective in matter is very useful conceptually and
numerically for understanding the form of the neutrino mass squared eigenstates
in matter and hence for calculating the matter oscillation probabilities.
Finally we analytically estimate the precision of this two-flavor approach and
numerically verify that it is precise at the sub-percent level.Comment: 9 pages, 6 figures, 1 table, comments welcom
Sensitivity of full-sky experiments to large scale cosmic ray anisotropies
The two main advantages of space-based observation of extreme energy
( eV) cosmic rays (EECRs) over ground based
observatories are the increased field of view and the full-sky coverage with
nearly uniform systematics across the entire sky. The former guarantees
increased statistics, whereas the latter enables a clean partitioning of the
sky into spherical harmonics. The discovery of anisotropies would help to
identify the long sought origin of EECRs. We begin an investigation of the
reach of a full-sky space-based experiment such as EUSO to detect anisotropies
in the extreme-energy cosmic-ray sky compared to ground based partial-sky
experiments such as the Pierre Auger Observatory and Telescope Array. The
technique is explained here, and simulations for a Universe with just two
nonzero multipoles, monopole plus either dipole or quadrupole, are presented.
These simulations quantify the advantages of space-based, all-sky coverage.Comment: 11 pages, 8 figure
The Galactic Contribution to IceCube's Astrophysical Neutrino Flux
High energy neutrinos have been detected by IceCube, but their origin remains
a mystery. Determining the sources of this flux is a crucial first step towards
multi-messenger studies. In this work we systematically compare two classes of
sources with the data: Galactic and extragalactic. We assume that the neutrino
sources are distributed according to a class of Galactic models. We build a
likelihood function on an event by event basis including energy, event
topology, absorption, and direction information. We present the probability
that each high energy event with deposited energy TeV in the
HESE sample is Galactic, extragalactic, or background. For Galactic models
considered the Galactic fraction of the astrophysical flux has a best fit value
of and is at 90\% CL. A zero Galactic flux is allowed at
.Comment: Updated with 6 year HESE data from IceCube, accepted for publication
in JCA
Neutrino oscillation probabilities through the looking glass
In this paper we review different expansions for neutrino oscillation
probabilities in matter in the context of long-baseline neutrino experiments.
We examine the accuracy and computational efficiency of different exact and
approximate expressions. We find that many of the expressions used in the
literature are not precise enough for the next generation of long-baseline
experiments, but several of them are while maintaining comparable simplicity.
The results of this paper can be used as guidance to both phenomenologists and
experimentalists when implementing the various oscillation expressions into
their analysis tools.Comment: 32 pages, 6 figure
Poisson-Boltzmann Theory of Charged Colloids: Limits of the Cell Model for Salty Suspensions
Thermodynamic properties of charge-stabilised colloidal suspensions are
commonly modeled by implementing the mean-field Poisson-Boltzmann (PB) theory
within a cell model. This approach models a bulk system by a single macroion,
together with counterions and salt ions, confined to a symmetrically shaped,
electroneutral cell. While easing solution of the nonlinear PB equation, the
cell model neglects microion-induced correlations between macroions, precluding
modeling of macroion ordering phenomena. An alternative approach, avoiding
artificial constraints of cell geometry, maps a macroion-microion mixture onto
a one-component model of pseudo-macroions governed by effective interactions.
In practice, effective-interaction models are usually based on linear screening
approximations, which can accurately describe nonlinear screening only by
incorporating an effective (renormalized) macroion charge. Combining charge
renormalization and linearized PB theories, in both the cell model and an
effective-interaction (cell-free) model, we compute osmotic pressures of highly
charged colloids and monovalent microions over a range of concentrations. By
comparing predictions with primitive model simulation data for salt-free
suspensions, and with predictions of nonlinear PB theory for salty suspensions,
we chart the limits of both the cell model and linear-screening approximations
in modeling bulk thermodynamic properties. Up to moderately strong
electrostatic couplings, the cell model proves accurate in predicting osmotic
pressures of deionized suspensions. With increasing salt concentration,
however, the relative contribution of macroion interactions grows, leading
predictions of the cell and effective-interaction models to deviate. No
evidence is found for a liquid-vapour phase instability driven by monovalent
microions. These results may guide applications of PB theory to soft materials.Comment: 27 pages, 5 figures, special issue of Journal of Physics: Condensed
Matter on "Classical density functional theory methods in soft and hard
matter
Charge Renormalization, Effective Interactions, and Thermodynamics of Deionized Colloidal Suspensions
Thermodynamic properties of charge-stabilised colloidal suspensions depend
sensitively on the effective charge of the macroions, which can be
substantially lower than the bare charge in the case of strong
counterion-macroion association. A theory of charge renormalization is
proposed, combining an effective one-component model of charged colloids with a
thermal criterion for distinguishing between free and associated counterions.
The theory predicts, with minimal computational effort, osmotic pressures of
deionized suspensions of highly charged colloids in close agreement with
large-scale simulations of the primitive model.Comment: 15 pages, 7 figure
Electroneutrality and Phase Behavior of Colloidal Suspensions
Several statistical mechanical theories predict that colloidal suspensions of
highly charged macroions and monovalent microions can exhibit unusual
thermodynamic phase behavior when strongly deionized. Density-functional,
extended Debye-H\"uckel, and response theories, within mean-field and
linearization approximations, predict a spinodal phase instability of charged
colloids below a critical salt concentration. Poisson-Boltzmann cell model
studies of suspensions in Donnan equilibrium with a salt reservoir demonstrate
that effective interactions and osmotic pressures predicted by such theories
can be sensitive to the choice of reference system, e.g., whether the microion
density profiles are expanded about the average potential of the suspension or
about the reservoir potential. By unifying Poisson-Boltzmann and response
theories within a common perturbative framework, it is shown here that the
choice of reference system is dictated by the constraint of global
electroneutrality. On this basis, bulk suspensions are best modeled by
density-dependent effective interactions derived from a closed reference system
in which the counterions are confined to the same volume as the macroions.
Linearized theories then predict bulk phase separation of deionized suspensions
only when expanded about a physically consistent (closed) reference system.
Lower-dimensional systems (e.g., monolayers, small clusters), depending on the
strength of macroion-counterion correlations, may be governed instead by
density-independent effective interactions tied to an open reference system
with counterions dispersed throughout the reservoir, possibly explaining
observed structural crossover in colloidal monolayers and anomalous
metastability of colloidal crystallites.Comment: 12 pages, 5 figures. Discussion clarified, references adde
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