2,222 research outputs found
Probabilistic metrology or how some measurement outcomes render ultra-precise estimates
We show on theoretical grounds that, even in the presence of noise,
probabilistic measurement strategies (which have a certain probability of
failure or abstention) can provide, upon a heralded successful outcome,
estimates with a precision that exceeds the deterministic bounds for the
average precision. This establishes a new ultimate bound on the phase
estimation precision of particular measurement outcomes (or sequence of
outcomes). For probe systems subject to local dephasing, we quantify such
precision limit as a function of the probability of failure that can be
tolerated. Our results show that the possibility of abstaining can set back the
detrimental effects of noise.Comment: Improved version of arXiv:1407.6910 with an extended introduction
where we clarify our approach to metrology, and probabilistic metrology in
particular. Changed titl
Constraining differential renormalization in abelian gauge theories
We present a procedure of differential renormalization at the one loop level
which avoids introducing unnecessary renormalization constants and
automatically preserves abelian gauge invariance. The amplitudes are expressed
in terms of a basis of singular functions. The local terms appearing in the
renormalization of these functions are determined by requiring consistency with
the propagator equation. Previous results in abelian theories, with and without
supersymmetry, are discussed in this context.Comment: 13 pages, LaTeX. Some equations corrected and a reference added.
Complete ps paper also available at http://www-ftae.ugr.es/papiros.html or
ftp://ftae3.ugr.es/pub/rmt/ugft73.p
Gluino signals in 4jet events and vertex tagging at LEP1
Heavy flavour tagging provides a broad range of possibilities in testing QCD
features at LEP. We present here a study of 4jets events at LEP I where the
so-called light gluinos could be directly produced. We show that microvertex
techniques offer a unique chance to exploit simple kinematical distributions in
order to optimise the signal coming from gluino production with respect to the
background of ordinary QCD events. Our results indicate that experimental
analyses along the lines suggested here can exclude or reveal the presence of a
gluino for masses up to 10 GeV and lifetimes below 10 sec. We also point
out that a large fraction of gluino events could decay in configurations
carrying large missing energy, so to escape the usual selection criteria of
4jet samples. In our study, mass effects of quarks and gluinos have been taken
into account exactly. Our results are independent from both the jet algorithm
and its resolution parameter.}Comment: 28 pages, 9 figures embedded with epsfig, Latex. Major revision
taking into account latest bounds. Version to appear in Zeit. f. Phys.
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