21,285 research outputs found
Lattice QCD study of the Boer-Mulders effect in a pion
The three-dimensional momenta of quarks inside a hadron are encoded in
transverse momentum-dependent parton distribution functions (TMDs). This work
presents an exploratory lattice QCD study of a TMD observable in the pion
describing the Boer-Mulders effect, which is related to polarized quark
transverse momentum in an unpolarized hadron. Particular emphasis is placed on
the behavior as a function of a Collins-Soper evolution parameter quantifying
the relative rapidity of the struck quark and the initial hadron, e.g., in a
semi-inclusive deep inelastic scattering (SIDIS) process. The lattice
calculation, performed at the pion mass m_pi = 518 MeV, utilizes a definition
of TMDs via hadronic matrix elements of a quark bilocal operator with a
staple-shaped gauge connection; in this context, the evolution parameter is
related to the staple direction. By parametrizing the aforementioned matrix
elements in terms of invariant amplitudes, the problem can be cast in a Lorentz
frame suited for the lattice calculation. In contrast to an earlier nucleon
study, due to the lower mass of the pion, the calculated data enable
quantitative statements about the physically interesting limit of large
relative rapidity. In passing, the similarity between the Boer-Mulders effects
extracted in the pion and the nucleon is noted.Comment: 16 pages, 9 figures, 3 table
Strings from position-dependent noncommutativity
We introduce a new set of noncommutative space-time commutation relations in
two space dimensions. The space-space commutation relations are deformations of
the standard flat noncommutative space-time relations taken here to have
position dependent structure constants. Some of the new variables are
non-Hermitian in the most natural choice. We construct their Hermitian
counterparts by means of a Dyson map, which also serves to introduce a new
metric operator. We propose PTlike symmetries, i.e.antilinear involutory maps,
respected by these deformations. We compute minimal lengths and momenta arising
in this space from generalized versions of Heisenberg's uncertainty relations
and find that any object in this two dimensional space is string like,
i.e.having a fundamental length in one direction beyond which a resolution is
impossible. Subsequently we formulate and partly solve some simple models in
these new variables, the free particle, its PT-symmetric deformations and the
harmonic oscillator.Comment: 11 pages, Late
Scalar production and decay to top quarks including interference effects at NLO in QCD in an EFT approach
Scalar and pseudo-scalar resonances decaying to top quarks are common
predictions in several scenarios beyond the standard model (SM) and are
extensively searched for by LHC experiments. Challenges on the experimental
side require optimising the strategy based on accurate predictions. Firstly,
QCD corrections are known to be large both for the SM QCD background and for
the pure signal scalar production. Secondly, leading order and approximate
next-to-leading order (NLO) calculations indicate that the interference between
signal and background is large and drastically changes the lineshape of the
signal, from a simple peak to a peak-dip structure. Therefore, a robust
prediction of this interference at NLO accuracy in QCD is necessary to ensure
that higher-order corrections do not alter the lineshapes. We compute the exact
NLO corrections, assuming a point-like coupling between the scalar and the
gluons and consistently embedding the calculation in an effective field theory
within an automated framework, and present results for a representative set of
beyond the SM benchmarks. The results can be further matched to parton shower
simulation, providing more realistic predictions. We find that NLO corrections
are important and lead to a significant reduction of the uncertainties. We also
discuss how our computation can be used to improve the predictions for physics
scenarios where the gluon-scalar loop is resolved and the effective approach is
less applicable.Comment: 32 pages, 17 figures; accepted versio
Heisenberg-style bounds for arbitrary estimates of shift parameters including prior information
A rigorous lower bound is obtained for the average resolution of any estimate
of a shift parameter, such as an optical phase shift or a spatial translation.
The bound has the asymptotic form k_I/ where G is the generator of the
shift (with an arbitrary discrete or continuous spectrum), and hence
establishes a universally applicable bound of the same form as the usual
Heisenberg limit. The scaling constant k_I depends on prior information about
the shift parameter. For example, in phase sensing regimes, where the phase
shift is confined to some small interval of length L, the relative resolution
\delta\hat{\Phi}/L has the strict lower bound (2\pi e^3)^{-1/2}/,
where m is the number of probes, each with generator G_1, and entangling joint
measurements are permitted. Generalisations using other resource measures and
including noise are briefly discussed. The results rely on the derivation of
general entropic uncertainty relations for continuous observables, which are of
interest in their own right.Comment: v2:new bound added for 'ignorance respecting estimates', some
clarification
QCD Tests from Tau Decays
The total hadronic width can be accurately calculated using
analyticity and the operator product expansion. The theoretical analysis of
this observable is updated to include all available perturbative and
non-perturbative corrections. The experimental determination of
and its actual uncertainties are discussed.Comment: 16 pages, latex, 3 Postscript figures, uses sprocl.sty, Invited Talk
at the 20th Johns Hopkins Workshop --Non Perturbative Particle Theory &
Experimental tests-- (Heidelberg, 27-29 June 1996
Strong unitary and overlap uncertainty relations: theory and experiment
We derive and experimentally investigate a strong uncertainty relation valid
for any unitary operators, which implies the standard uncertainty relation
as a special case, and which can be written in terms of geometric phases. It is
saturated by every pure state of any -dimensional quantum system, generates
a tight overlap uncertainty relation for the transition probabilities of any
pure states, and gives an upper bound for the out-of-time-order
correlation function. We test these uncertainty relations experimentally for
photonic polarisation qubits, including the minimum uncertainty states of the
overlap uncertainty relation, via interferometric measurements of generalised
geometric phases.Comment: 5 pages of main text, 5 pages of Supplemental Material.
Clarifications added in this updated versio
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