4,803 research outputs found
Algorithmic Verification of Asynchronous Programs
Asynchronous programming is a ubiquitous systems programming idiom to manage
concurrent interactions with the environment. In this style, instead of waiting
for time-consuming operations to complete, the programmer makes a non-blocking
call to the operation and posts a callback task to a task buffer that is
executed later when the time-consuming operation completes. A co-operative
scheduler mediates the interaction by picking and executing callback tasks from
the task buffer to completion (and these callbacks can post further callbacks
to be executed later). Writing correct asynchronous programs is hard because
the use of callbacks, while efficient, obscures program control flow.
We provide a formal model underlying asynchronous programs and study
verification problems for this model. We show that the safety verification
problem for finite-data asynchronous programs is expspace-complete. We show
that liveness verification for finite-data asynchronous programs is decidable
and polynomial-time equivalent to Petri Net reachability. Decidability is not
obvious, since even if the data is finite-state, asynchronous programs
constitute infinite-state transition systems: both the program stack and the
task buffer of pending asynchronous calls can be potentially unbounded.
Our main technical construction is a polynomial-time semantics-preserving
reduction from asynchronous programs to Petri Nets and conversely. The
reduction allows the use of algorithmic techniques on Petri Nets to the
verification of asynchronous programs.
We also study several extensions to the basic models of asynchronous programs
that are inspired by additional capabilities provided by implementations of
asynchronous libraries, and classify the decidability and undecidability of
verification questions on these extensions.Comment: 46 pages, 9 figure
Quantum electrodynamics of relativistic bound states with cutoffs
We consider an Hamiltonian with ultraviolet and infrared cutoffs, describing
the interaction of relativistic electrons and positrons in the Coulomb
potential with photons in Coulomb gauge. The interaction includes both
interaction of the current density with transversal photons and the Coulomb
interaction of charge density with itself. We prove that the Hamiltonian is
self-adjoint and has a ground state for sufficiently small coupling constants.Comment: To appear in "Journal of Hyperbolic Differential Equation
Constraints on new interactions from neutron scattering experiments
Constraints for the constants of hypothetical Yukawa-type corrections to the
Newtonian gravitational potential are obtained from analysis of neutron
scattering experiments. Restrictions are obtained for the interaction range
between 10^{-12} and 10^{-7} cm, where Casimir force experiments and atomic
force microscopy are not sensitive. Experimental limits are obtained also for
non-electromagnetic inverse power law neutron-nucleus potential. Some
possibilities are discussed to strengthen these constraints.Comment: 18 pages, 3 figure
Non-relativistic effective theory of dark matter direct detection
Dark matter direct detection searches for signals coming from dark matter
scattering against nuclei at a very low recoil energy scale ~ 10 keV. In this
paper, a simple non-relativistic effective theory is constructed to describe
interactions between dark matter and nuclei without referring to any underlying
high energy models. It contains the minimal set of operators that will be
tested by direct detection. The effective theory approach highlights the set of
distinguishable recoil spectra that could arise from different theoretical
models. If dark matter is discovered in the near future in direct detection
experiments, a measurement of the shape of the recoil spectrum will provide
valuable information on the underlying dynamics. We bound the coefficients of
the operators in our non-relativistic effective theory by the null results of
current dark matter direct detection experiments. We also discuss the mapping
between the non-relativistic effective theory and field theory models or
operators, including aspects of the matching of quark and gluon operators to
nuclear form factors.Comment: 35 pages, 3 figures, Appendix C.3 revised, acknowledgments and
references adde
Pair production of the T-odd leptons at the LHC
The T-odd leptons predicted by the littlest model with T-parity can
be pair produced via the subprocesses ,
, and (= or
) at the Large Hadron Collider . We estimate the hadronic
production cross sections for all of these processes and give a simply
phenomenology analysis. We find that the cross sections for most of the above
processes are very small. However, the value of the cross section for the
process can reach .Comment: 12 pages, 2 figure
Measuring the Polarization of Boosted Hadronic Tops
We propose a new technique for measuring the polarization of hadronically
decaying boosted top quarks. In particular, we apply a subjet-based technique
to events where the decay products of the top are clustered within a single
jet. The technique requires neither b-tagging nor W-reconstruction, and does
not rely on assumptions about either the top production mechanism or the
sources of missing energy in the event. We include results for various new
physics scenarios made with different Monte Carlo generators to demonstrate the
robustness of the technique.Comment: v2: version accepted for publication in JHE
New Physics Signals in Longitudinal Gauge Boson Scattering at the LHC
We introduce a novel technique designed to look for signatures of new physics
in vector boson fusion processes at the TeV scale. This functions by measuring
the polarization of the vector bosons to determine the relative longitudinal to
transverse production. In studying this ratio we can directly probe the high
energy E^2-growth of longitudinal vector boson scattering amplitudes
characteristic of models with non-Standard Model (SM) interactions. We will
focus on studying models parameterized by an effective Lagrangian that include
a light Higgs with non-SM couplings arising from TeV scale new physics
associated with the electroweak symmetry breaking, although our technique can
be used in more general scenarios. We will show that this technique is stable
against the large uncertainties that can result from variations in the
factorization scale, improving upon previous studies that measure cross section
alone
Chiral U(1) flavor models and flavored Higgs doublets: the top FB asymmetry and the Wjj
We present U(1) flavor models for leptophobic Z' with flavor dependent
couplings to the right-handed up-type quarks in the Standard Model, which can
accommodate the recent data on the top forward-backward (FB) asymmetry and the
dijet resonance associated with a W boson reported by CDF Collaboration. Such
flavor-dependent leptophobic charge assignments generally require extra chiral
fermions for anomaly cancellation. Also the chiral nature of U(1)' flavor
symmetry calls for new U(1)'-charged Higgs doublets in order for the SM
fermions to have realistic renormalizable Yukawa couplings. The stringent
constraints from the top FB asymmetry at the Tevatron and the same sign top
pair production at the LHC can be evaded due to contributions of the extra
Higgs doublets. We also show that the extension could realize cold dark matter
candidates.Comment: 40 pages, 10 figures, added 1 figure and extended discussion,
accepted for publication in JHE
Multi-Photon Signals from Composite Models at LHC
We analyze the collider signals of composite scalars that emerge in certain
little Higgs models and models of vectorlike confinement. Similar to the decay
of the pion into photon pairs, these scalars mainly decay through
anomaly-induced interactions into electroweak gauge bosons, leading to a
distinct signal with three or more photons in the final state. We study the
standard model backgrounds for these signals, and find that the LHC can
discover these models over a large range of parameter space with 30 fb
at 14 TeV. An early discovery at the current 7 TeV run is possible in some
regions of parameter space. We also discuss possibilities to measure the spin
of the particles in the and decay channels.Comment: 18 pages, LaTe
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