537 research outputs found
Link Invariants of Finite Type and Perturbation Theory
The Vassiliev-Gusarov link invariants of finite type are known to be closely
related to perturbation theory for Chern-Simons theory. In order to clarify the
perturbative nature of such link invariants, we introduce an algebra V_infinity
containing elements g_i satisfying the usual braid group relations and elements
a_i satisfying g_i - g_i^{-1} = epsilon a_i, where epsilon is a formal variable
that may be regarded as measuring the failure of g_i^2 to equal 1.
Topologically, the elements a_i signify crossings. We show that a large class
of link invariants of finite type are in one-to-one correspondence with
homogeneous Markov traces on V_infinity. We sketch a possible application of
link invariants of finite type to a manifestly diffeomorphism-invariant
perturbation theory for quantum gravity in the loop representation.Comment: 11 page
4-Dimensional BF Theory as a Topological Quantum Field Theory
Starting from a Lie group G whose Lie algebra is equipped with an invariant
nondegenerate symmetric bilinear form, we show that 4-dimensional BF theory
with cosmological term gives rise to a TQFT satisfying a generalization of
Atiyah's axioms to manifolds equipped with principal G-bundle. The case G =
GL(4,R) is especially interesting because every 4-manifold is then naturally
equipped with a principal G-bundle, namely its frame bundle. In this case, the
partition function of a compact oriented 4-manifold is the exponential of its
signature, and the resulting TQFT is isomorphic to that constructed by Crane
and Yetter using a state sum model, or by Broda using a surgery presentation of
4-manifolds.Comment: 15 pages in LaTe
Braneworld Flux Inflation
We propose a geometrical model of brane inflation where inflation is driven
by the flux generated by opposing brane charges and terminated by the collision
of the branes, with charge annihilation. We assume the collision process is
completely inelastic and the kinetic energy is transformed into the thermal
energy after collision. Thereafter the two branes coalesce together and behave
as a single brane universe with zero effective cosmological constant. In the
Einstein frame, the 4-dimensional effective theory changes abruptly at the
collision point. Therefore, our inflationary model is necessarily 5-dimensional
in nature. As the collision process has no singularity in 5-dimensional
gravity, we can follow the evolution of fluctuations during the whole history
of the universe. It turns out that the radion field fluctuations have a steeply
tilted, red spectrum, while the primordial gravitational waves have a flat
spectrum. Instead, primordial density perturbations could be generated by a
curvaton mechanism.Comment: 11 pages, 6 figures, references adde
Test of the photon detection system for the LHCb RICH Upgrade in a charged particle beam
The LHCb detector will be upgraded to make more efficient use of the
available luminosity at the LHC in Run III and extend its potential for
discovery. The Ring Imaging Cherenkov detectors are key components of the LHCb
detector for particle identification. In this paper we describe the setup and
the results of tests in a charged particle beam, carried out to assess
prototypes of the upgraded opto-electronic chain from the Multi-Anode PMT
photosensor to the readout and data acquisition system.Comment: 25 pages, 22 figure
Physically meaningful and not so meaningful symmetries in Chern-Simons theory
We explicitly show that the Landau gauge supersymmetry of Chern-Simons theory
does not have any physical significance. In fact, the difference between an
effective action both BRS invariant and Landau supersymmetric and an effective
action only BRS invariant is a finite field redefinition. Having established
this, we use a BRS invariant regulator that defines CS theory as the large mass
limit of topologically massive Yang-Mills theory to discuss the shift k \to
k+\cv of the bare Chern-Simons parameter in conncection with the Landau
supersymmetry. Finally, to convince ourselves that the shift above is not an
accident of our regularization method, we comment on the fact that all BRS
invariant regulators used as yet yield the same value for the shift.Comment: phyzzx, 21 pages, 2 figures in one PS fil
A Cylindrical GEM Inner Tracker for the BESIII experiment at IHEP
The Beijing Electron Spectrometer III (BESIII) is a multipurpose detector
that collects data provided by the collision in the Beijing Electron Positron
Collider II (BEPCII), hosted at the Institute of High Energy Physics of
Beijing. Since the beginning of its operation, BESIII has collected the world
largest sample of J/{\psi} and {\psi}(2s). Due to the increase of the
luminosity up to its nominal value of 10^33 cm-2 s-1 and aging effect, the MDC
decreases its efficiency in the first layers up to 35% with respect to the
value in 2014. Since BESIII has to take data up to 2022 with the chance to
continue up to 2027, the Italian collaboration proposed to replace the inner
part of the MDC with three independent layers of Cylindrical triple-GEM (CGEM).
The CGEM-IT project will deploy several new features and innovation with
respect the other current GEM based detector: the {\mu}TPC and analog readout,
with time and charge measurements will allow to reach the 130 {\mu}m spatial
resolution in 1 T magnetic field requested by the BESIII collaboration. In this
proceeding, an update of the status of the project will be presented, with a
particular focus on the results with planar and cylindrical prototypes with
test beams data. These results are beyond the state of the art for GEM
technology in magnetic field
First Observation and Measurement of the Decay K+- -> pi+- e+ e- gamma
Using the full data set of the NA48/2 experiment, the decay K+- -> pi+- e+ e-
gamma is observed for the first time, selecting 120 candidates with 7.3 +- 1.7
estimated background events. With K+- -> pi+- pi0D as normalisation channel,
the branching ratio is determined in a model-independent way to be Br(K+- ->
pi+- e+ e- gamma, m_eegamma > 260 MeV/c^2) = (1.19 +- 0.12_stat +- 0.04_syst) x
10^-8. This measured value and the spectrum of the e+ e- gamma invariant mass
allow a comparison with predictions of Chiral Perturbation Theory.Comment: 13 pages, 3 figures. Accepted for publication in Phys.Lett.
Medial temporal lobe atrophy and posterior atrophy scales normative values
OBJECTIVES: The medial temporal lobe atrophy (MTA) and the posterior atrophy (PA) scales allow to assess the degree hippocampal and parietal atrophy from magnetic resonance imaging (MRI) scans. Despite reliable, easy and widespread employment, appropriate normative values are still missing. We aim to provide norms for the Italian population. // METHODS: Two independent raters assigned the highest MTA and PA score between hemispheres, based on 3D T1-weighted MRI of 936 Italian Brain Normative Archive subjects (age: mean ± SD: 50.2 ± 14.7, range: 20-84; MMSE>26 or CDR = 0). The inter-rater agreement was assessed with the absolute intraclass correlation coefficient (aICC). We assessed the association between MTA and PA scores and sociodemographic features and APOE status, and normative data were established by age decade based on percentile distributions. // RESULTS: Raters agreed in 90% of cases for MTA (aICC = 0.86; 95% CI = 0.69-0.98) and in 86% for PA (aICC = 0.82; 95% CI = 0.58-0.98). For both rating scales, score distribution was skewed, with MTA = 0 in 38% of the population and PA = 0 in 52%, while a score ≥ 2 was only observed in 12% for MTA and in 10% for PA. Median denoted overall hippocampal (MTA: median = 1, IQR = 0-1) and parietal (PA: median = 0, IQR = 0-1) integrity. The 90th percentile of the age-specific distributions increased from 1 (at age 20-59) for both scales, to 2 for PA over age 60, and up to 4 for MTA over age 80. Gender, education and APOE status did not significantly affect the percentile distributions in the whole sample, nor in the subset over age 60. // CONCLUSIONS: Our normative data for the MTA and PA scales are consistent with previous studies and overcome their main limitations (in particular uneven representation of ages and missing percentile distributions), defining the age-specific norms to be considered for proper brain atrophy assessment
Empirical parameterization of the K+- -> pi+- pi0 pi0 decay Dalitz plot
As first observed by the NA48/2 experiment at the CERN SPS, the \p0p0
invariant mass (M00) distribution from \kcnn decay shows a cusp-like anomaly
at M00=2m+, where m+ is the charged pion mass. An analysis to extract the pi pi
scattering lengths in the isospin I=0 and I=2 states, a0 and a2, respectively,
has been recently reported. In the present work the Dalitz plot of this decay
is fitted to a new empirical parameterization suitable for practical purposes,
such as Monte Carlo simulations of K+- -> pi+- pi0 pi0 decays.Comment: 9 pages, 3 figures
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