6,040 research outputs found
Perturbative and non-perturbative renormalization results of the Chromomagnetic Operator on the Lattice
The Chromomagnetic operator (CMO) mixes with a large number of operators
under renormalization. We identify which operators can mix with the CMO, at the
quantum level. Even in dimensional regularization (DR), which has the simplest
mixing pattern, the CMO mixes with a total of 9 other operators, forming a
basis of dimension-five, Lorentz scalar operators with the same flavor content
as the CMO. Among them, there are also gauge noninvariant operators; these are
BRST invariant and vanish by the equations of motion, as required by
renormalization theory. On the other hand using a lattice regularization
further operators with will mix; choosing the lattice action in a
manner as to preserve certain discrete symmetries, a minimul set of 3
additional operators (all with ) will appear. In order to compute all
relevant mixing coefficients, we calculate the quark-antiquark (2-pt) and the
quark-antiquark-gluon (3-pt) Green's functions of the CMO at nonzero quark
masses. These calculations were performed in the continuum (dimensional
regularization) and on the lattice using the maximally twisted mass fermion
action and the Symanzik improved gluon action. In parallel, non-perturbative
measurements of the matrix element are being performed in simulations
with 4 dynamical () twisted mass fermions and the Iwasaki improved
gluon action.Comment: 7 pages, 1 figure, 3 tables, LATTICE2014 proceeding
The chromomagnetic operator on the lattice
We study matrix elements of the "chromomagnetic" operator on the lattice.
This operator is contained in the strangeness-changing effective Hamiltonian
which describes electroweak effects in the Standard Model and beyond.
Having dimension 5, the chromomagnetic operator is characterized by a rich
pattern of mixing with other operators of equal and lower dimensionality,
including also non gauge invariant quantities; it is thus quite a challenge to
extract from lattice simulations a clear signal for the hadronic matrix
elements of this operator.
We compute all relevant mixing coefficients to one loop in lattice
perturbation theory; this necessitates calculating both 2-point
(quark-antiquark) and 3-point (gluon-quark-antiquark) Green's functions at
nonzero quark masses. We use the twisted mass lattice formulation, with
Symanzik improved gluon action.
For a comprehensive presentation of our results, along with detailed
explanations and a more complete list of references, we refer to our
forthcoming publication [1].Comment: 7 pages, 1 figure. Talk presented at the 31st International Symposium
on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz,
German
matrix elements of the chromomagnetic operator on the lattice
We present the results of the first lattice QCD calculation of the matrix elements of the chromomagnetic operator , which appears in the effective Hamiltonian
describing transitions in and beyond the Standard Model. Having
dimension 5, the chromomagnetic operator is characterized by a rich pattern of
mixing with operators of equal and lower dimensionality. The multiplicative
renormalization factor as well as the mixing coefficients with the operators of
equal dimension have been computed at one loop in perturbation theory. The
power divergent coefficients controlling the mixing with operators of lower
dimension have been determined non-perturbatively, by imposing suitable
subtraction conditions. The numerical simulations have been carried out using
the gauge field configurations produced by the European Twisted Mass
Collaboration with dynamical quarks at three values of the
lattice spacing. Our result for the B-parameter of the chromomagnetic operator
at the physical pion and kaon point is , while
in the SU(3) chiral limit we obtain . Our findings are
significantly smaller than the model-dependent estimate ,
currently used in phenomenological analyses, and improve the uncertainty on
this important phenomenological quantity.Comment: 20 pages, 4 figures, 2 table. Refined SU(3) ChPT analysis with no
changes in the final result. Version to appear in PR
A decomposition approach for multidimensional knapsacks with family-split penalties
The optimization of Multidimensional Knapsacks with Family-Split Penalties has been introduced in the literature as a variant of the more classical Multidimensional Knapsack and Multi-Knapsack problems. This problem deals with a set of items partitioned in families, and when a single item is picked to maximize the utility, then all items in its family must be picked. Items from the same family can be assigned to different knapsacks, and in this situation split penalties are paid. This problem arises in real applications in various fields. This paper proposes a new exact and fast algorithm based on a specific Combinatorial Benders Cuts scheme. An extensive experimental campaign computationally shows the validity of the proposed method and its superior performance compared to both commercial solvers and state-of-the-art approaches. The paper also addresses algorithmic flexibility and scalability issues, investigates challenging cases, and analyzes the impact of problem parameters on the algorithm behavior. Moreover, it shows the applicability of the proposed approach to a wider class of realistic problems, including fixed costs related to each knapsack utilization. Finally, further possible research directions are considered
Gallium Oxide and Dioxide: Investigation of the Ground and Low-Lying Electronic States via Anion Photoelectron Spectroscopy
The GaO and GaO2 molecules were investigated using negative ion photoelectron spectroscopy. All the photoelectron spectra showed vibrationally resolved progressions. With the aid of electronic structure calculations and Franck-Condon spectral simulations, different molecular parameters and energetics of GaO-/GaO and GaO2-/GaO2 were determined, including the electron affinity of GaO, the vibrational frequency of GaO-, and the term energy, spin-orbit splitting, and vibrational frequency for the first excited A 2PiOmega state of GaO. The GaO2- photoelectron spectra comprised three bands assigned as transitions from the linear X 1Sigma(g)+ ground state of GaO2- to three linear neutral states: the A 2Pi(g), B 2Pi(u), and C 2Sigma(u) + states. The symmetric stretch frequencies of the anion and three neutral states as well as the spin-orbit splitting of the neutral 2Pi states were determined. Electronic structure calculations found the neutral lowest energy linear structure to be only 63 meV higher than the neutral bent geometry
Prognostic impact of coronary microcirculation abnormalities in systemic sclerosis: a prospective study to evaluate the role of non-invasive tests
INTRODUCTION: Microcirculation dysfunction is a typical feature of systemic sclerosis (SSc) and represents the earliest abnormality of primary myocardial involvement. We assessed coronary microcirculation status by combining two functional tests in SSc patients and estimating its impact on disease outcome.
METHODS: Forty-one SSc patients, asymptomatic for coronary artery disease, were tested for coronary flow velocity reserve (CFR) by transthoracic-echo-Doppler with adenosine infusion (A-TTE) and for left ventricular wall motion abnormalities (WMA) by dobutamine stress echocardiography (DSE). Myocardial multi-detector computed tomography (MDCT) enabled the presence of epicardial stenosis, which could interfere with the accuracy of the tests, to be excluded. Patient survival rate was assessed over a 6.7- ± 3.5-year follow-up.
RESULTS: Nineteen out of 41 (46%) SSc patients had a reduced CFR (≤2.5) and in 16/41 (39%) a WMA was observed during DSE. Furthermore, 13/41 (32%) patients showed pathological CFR and WMA. An inverse correlation between wall motion score index (WMSI) during DSE and CFR value (r = -0.57, P <0.0001) was observed; in addition, CFR was significantly reduced (2.21 ± 0.38) in patients with WMA as compared to those without (2.94 ± 0.60) (P <0.0001). In 12 patients with abnormal DSE, MDCT was used to exclude macrovasculopathy. During a 6.7- ± 3.5-year follow-up seven patients with abnormal coronary functional tests died of disease-related causes, compared to only one patient with normal tests.
CONCLUSIONS: A-TTE and DSE tests are useful tools to detect non-invasively pre-clinical microcirculation abnormalities in SSc patients; moreover, abnormal CFR and WMA might be related to a worse disease outcome suggesting a prognostic value of these tests, similar to other myocardial diseases
Stochastic Coherence Over Attention Trajectory For Continuous Learning In Video Streams
Devising intelligent agents able to live in an environment and learn by observing the surroundings is a longstanding goal of Artificial Intelligence. From a bare Machine Learning perspective, challenges arise when the agent is prevented from leveraging large fully-annotated dataset, but rather the interactions with supervisory signals are sparsely distributed over space and time. This paper proposes a novel neural-network-based approach to progressively and autonomously develop pixel-wise representations in a video stream. The proposed method is based on a human-like attention mechanism that allows the agent to learn by observing what is moving in the attended locations. Spatio-temporal stochastic coherence along the attention trajectory, paired with a contrastive term, leads to an unsupervised learning criterion that naturally copes with the considered setting. Differently from most existing works, the learned representations are used in open-set class-incremental classification of each frame pixel, relying on few supervisions. Our experiments leverage 3D virtual environments and they show that the proposed agents can learn to distinguish objects just by observing the video stream. Inheriting features from state-of-the art models is not as powerful as one might expect
The Ross Shelf cavity water exchange variability during 1995-1998
This work aims at presenting an analysis of the evolution of the physical properties of a water column at the southern limit of the Ross Sea, Antarctica. Data has been collected over a four year period (from January 1995 to July
1998) by means of an oceanographic mooring (named mooring “F”) berthed a few miles north of theRoss IceShe lf at a depth of 600 m on thecon tinental shelf. The
velocity and temperature measurements have been investigated seeking for ISW (Ice Shelf Water) outflow footprints. These outflows are irregular massive injections of cold water from below the Ice Shelf, flowing mainly across the cavity floor into the Ross Sea bottom layers. The study evidenced a large number of DISW outflow events (Deep Ice Shelf Water, the coldest and densest fraction of the ISW, the actual main object of the present study), characterized by an interannual variability that could turn out to bean important co-factor in thev ariations of theplane tary heat balance and climate instability. Differences in DISW outflow timings from biennium
1995-1996, during which a jet-like behaviour was dominating (each events was only a few days long), and 1997-1998 (with a few long and rather continous cold water outflows) have been detected. Moreover, in 1996 measurements evidenced a
relatively long and warm period (about 110 days from March to July) characterized by thetotal absenceof DISW outflow, this interval being morethan twice longer with respect to any other similar ones registered during 1995, 1997 and 1998, and longer that any other warm period observed in the area during the early ’80s. The estimates of cold water exchanged during the four years return a more complicated
framework: 1996 behaviour seems to be closer to the 1997 than to the 1995 one, with high fluxes and high volumes. 1995 can probably be considered as the ignition of an interannual anomaly, which climax is the long warm period of spring 1996
- …