138 research outputs found
Constraining CP violation in neutral meson mixing with theory input
There has been a lot of recent interest in the experimental hints of CP
violation in B_{d,s}^0 mixing, which would be a clear signal of beyond the
standard model physics (with higher significance). We derive a new relation for
the mixing parameters, which allows clearer interpretation of the data in
models in which new physics enters in M_12 and/or \Gamma_12. Our results imply
that the central value of the D\O\ measurement of the semileptonic CP asymmetry
in B_{d,s}^0 decay is not only in conflict with the standard model, but in a
stronger tension with data on \Delta\Gamma_s than previously appreciated. This
result can be used to improve the constraint on \Delta\Gamma or A_SL, whichever
is less precisely measured.Comment: 5 pages, 2 figures, informed of prior derivation of eq. (21), title
modifie
Noise Injection Node Regularization for Robust Learning
We introduce Noise Injection Node Regularization (NINR), a method of
injecting structured noise into Deep Neural Networks (DNN) during the training
stage, resulting in an emergent regularizing effect. We present theoretical and
empirical evidence for substantial improvement in robustness against various
test data perturbations for feed-forward DNNs when trained under NINR. The
novelty in our approach comes from the interplay of adaptive noise injection
and initialization conditions such that noise is the dominant driver of
dynamics at the start of training. As it simply requires the addition of
external nodes without altering the existing network structure or optimization
algorithms, this method can be easily incorporated into many standard problem
specifications. We find improved stability against a number of data
perturbations, including domain shifts, with the most dramatic improvement
obtained for unstructured noise, where our technique outperforms other existing
methods such as Dropout or regularization, in some cases. We further show
that desirable generalization properties on clean data are generally
maintained.Comment: 16 pages, 9 figure
A new basis for Hamiltonian SU(2) simulations
Due to rapidly improving quantum computing hardware, Hamiltonian simulations
of relativistic lattice field theories have seen a resurgence of attention.
This computational tool requires turning the formally infinite-dimensional
Hilbert space of the full theory into a finite-dimensional one. For gauge
theories, a widely-used basis for the Hilbert space relies on the
representations induced by the underlying gauge group, with a truncation that
keeps only a set of the lowest dimensional representations. This works well at
large bare gauge coupling, but becomes less efficient at small coupling, which
is required for the continuum limit of the lattice theory. In this work, we
develop a new basis suitable for the simulation of an SU(2) lattice gauge
theory in the maximal tree gauge. In particular, we show how to perform a
Hamiltonian truncation so that the eigenvalues of both the magnetic and
electric gauge-fixed Hamiltonian are mostly preserved, which allows for this
basis to be used at all values of the coupling. Little prior knowledge is
assumed, so this may also be used as an introduction to the subject of
Hamiltonian formulations of lattice gauge theories.Comment: 27 pages, 11 figure
Light dark forces at flavor factories
SuperB experiment could represent an ideal environment to test a new U (1)
symmetry related to light dark forces candidates. A promising discovery channel
is represented by the resonant production of a boson U, followed by its decay
into lepton pairs. Beyond approximations adopted in the literature, an exact
tree level calculation of the radiative processes and corresponding QED
backgrounds is performed, including also the most important higher-order
corrections. The calculation is implemented in a release of the generator
BabaYaga@NLO useful for data analysis and interpretation. The distinct features
of U boson production are shown and the statistical significance is analysed
Singlet Portal to the Hidden Sector
Ultraviolet physics typically induces a kinetic mixing between gauge singlets
which is marginal and hence non-decoupling in the infrared. In singlet
extensions of the minimal supersymmetric standard model, e.g. the
next-to-minimal supersymmetric standard model, this furnishes a well motivated
and distinctive portal connecting the visible sector to any hidden sector which
contains a singlet chiral superfield. In the presence of singlet kinetic
mixing, the hidden sector automatically acquires a light mass scale in the
range 0.1 - 100 GeV induced by electroweak symmetry breaking. In theories with
R-parity conservation, superparticles produced at the LHC invariably cascade
decay into hidden sector particles. Since the hidden sector singlet couples to
the visible sector via the Higgs sector, these cascades necessarily produce a
Higgs boson in an order 0.01 - 1 fraction of events. Furthermore,
supersymmetric cascades typically produce highly boosted, low-mass hidden
sector singlets decaying visibly, albeit with displacement, into the heaviest
standard model particles which are kinematically accessible. We study
experimental constraints on this broad class of theories, as well as the role
of singlet kinetic mixing in direct detection of hidden sector dark matter. We
also present related theories in which a hidden sector singlet interacts with
the visible sector through kinetic mixing with right-handed neutrinos.Comment: 12 pages, 5 figure
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Readout of TPC Tracking Chambers with GEMs and Pixel Chip
Two layers of GEMs and the ATLAS Pixel Chip, FEI3, have been combined and tested as a prototype for Time Projection Chamber (TPC) readout at the International Linear Collider (ILC). The double-layer GEM system amplifies charge with gain sufficient to detect all track ionization. The suitability of three gas mixtures for this application was investigated, and gain measurements are presented. A large sample of cosmic ray tracks was reconstructed in 3D by using the simultaneous timing and 2D spatial information from the pixel chip. The chip provides pixel charge measurement as well as timing. These results demonstrate that a double GEM and pixel combination, with a suitably modified pixel ASIC, could meet the stringent readout requirements of the ILC
Dark Force Detection in Low Energy e-p Collisions
We study the prospects for detecting a light boson X with mass m_X < 100 MeV
at a low energy electron-proton collider. We focus on the case where X
dominantly decays to e+ e- as motivated by recent "dark force" models. In order
to evade direct and indirect constraints, X must have small couplings to the
standard model (alpha_X 10 MeV).
By comparing the signal and background cross sections for the e- p e+ e- final
state, we conclude that dark force detection requires an integrated luminosity
of around 1 inverse attobarn, achievable with a forthcoming JLab proposal.Comment: 38 pages, 19 figures; v2, references adde
Proceedings of the 2nd Workshop on Flavor Symmetries and Consequences in Accelerators and Cosmology (FLASY12)
These are the proceedings of the 2nd Workshop on Flavor Symmetries and
Consequences in Accelerators and Cosmology, held 30 June 2012 - 4 July 2012,
Dortmund, Germany.Comment: Order 400 pages, several figures including the group picture v2:
corrected author list and contributio
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