4,601 research outputs found
Physics reach of CERN-based SuperBeam neutrino oscillation experiments
We compare the physics potential of two representative options for a
SuperBeam in Europe, studying the achievable precision at 1\sigma with which
the CP violation phase (\delta) could be measured, as well as the mass
hierarchy and CP violation discovery potentials. The first setup corresponds to
a high energy beam aiming from CERN to a 100 kt liquid argon detector placed at
the Pyh\"asalmi mine (2300 km), one of the LAGUNA candidate sites. The second
setup corresponds to a much lower energy beam, aiming from CERN to a 500 kt
water \v{C}erenkov detector placed at the Gran Sasso underground laboratory
(730 km). This second option is also studied for a baseline of 650 km,
corresponding to the LAGUNA candidate sites of Umbria and the Canfranc
underground laboratory. All results are presented also for scenarios with
statistics lowered by factors of 2, 4, 8 and 16 to study the possible
reductions of flux, detector mass or running time allowed by the large value of
\theta_{13} recently measured.Comment: 15 pages, 4 figure
Reassessing the sensitivity to leptonic CP violation
We address the validity of the usual procedure to determine the sensitivity
of neutrino oscillation experiments to CP violation. An explicit calibration of
the test statistic is performed through Monte Carlo simulations for several
experimental setups. We find that significant deviations from a
distribution with one degree of freedom occur for experimental setups with low
sensitivity to . In particular, when the allowed region to which
is constrained at a given confidence level is comparable to the whole
allowed range, the cyclic nature of the variable manifests and the premises of
Wilk's theorem are violated. This leads to values of the test statistic
significantly lower than a distribution at that confidence level. On
the other hand, for facilities which can place better constraints on
the cyclic nature of the variable is hidden and, as the potential of the
facility improves, the values of the test statistics first become slightly
higher than and then approach asymptotically a distribution. The role
of sign degeneracies is also discussed.Comment: 14 pages, 5 figures, RevTeX4. The discussion of the results has been
improved and considerably extended. Version accepted for publication in JHE
Freeze-in through portals
The popular freeze-out paradigm for Dark Matter (DM) production, relies on
DM-baryon couplings of the order of the weak interactions. However, different
search strategies for DM have failed to provide a conclusive evidence of such
(non-gravitational) interactions, while greatly reducing the parameter space of
many representative models. This motivates the study of alternative mechanisms
for DM genesis. In the freeze-in framework, the DM is slowly populated from the
thermal bath while never reaching equilibrium. In this work, we analyse in
detail the possibility of producing a frozen-in DM via a mediator particle
which acts as a portal. We give analytical estimates of different freeze-in
regimes and support them with full numerical analyses, taking into account the
proper distribution functions of bath particles. Finally, we constrain the
parameter space of generic models by requiring agreement with DM relic
abundance observations.Comment: 18 pages, 6 figure
Numerical controllability of the wave equation through primal methods and Carleman estimates
This paper deals with the numerical computation of boundary null controls for
the 1D wave equation with a potential. The goal is to compute an approximation
of controls that drive the solution from a prescribed initial state to zero at
a large enough controllability time. We do not use in this work duality
arguments but explore instead a direct approach in the framework of global
Carleman estimates. More precisely, we consider the control that minimizes over
the class of admissible null controls a functional involving weighted integrals
of the state and of the control. The optimality conditions show that both the
optimal control and the associated state are expressed in terms of a new
variable, the solution of a fourth-order elliptic problem defined in the
space-time domain. We first prove that, for some specific weights determined by
the global Carleman inequalities for the wave equation, this problem is
well-posed. Then, in the framework of the finite element method, we introduce a
family of finite-dimensional approximate control problems and we prove a strong
convergence result. Numerical experiments confirm the analysis. We complete our
study with several comments
Monte Carlo simulation of recrystallization
A Monte Carlo computer simulation technique, in which a continuum system is modeled employing a discrete lattice, has been applied to the problem of recrystallization. Primary recrystallization is modeled under conditions where the degree of stored energy is varied and nucleation occurs homogeneously (without regard for position in the microstructure). The nucleation rate is chosen as site saturated. Temporal evolution of the simulated microstructures is analyzed to provide the time dependence of the recrystallized volume fraction and grain sizes. The recrystallized volume fraction shows sigmoidal variations with time. The data are approximately fit by the Johnson-Mehl-Avrami equation with the expected exponents, however significant deviations are observed for both small and large recrystallized volume fractions. Under constant rate nucleation conditions, the propensity for irregular grain shapes is decreased and the density of two sided grains increases
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