118 research outputs found
Radiative corrections to decay amplitudes in lattice QCD
The precision of lattice QCD computations of many quantities has reached such
a precision that isospin-breaking corrections, including electromagnetism, must
be included if further progress is to be made in extracting fundamental
information, such as the values of Cabibbo-Kobayashi-Maskawa matrix elements,
from experimental measurements. We discuss the framework for including
radiative corrections in leptonic and semileptonic decays of hadrons, including
the treatment of infrared divergences. We briefly review isospin breaking in
leptonic decays and present the first numerical results for the ratio
in which these corrections have been
included. We also discuss the additional theoretical issues which arise when
including electromagnetic corrections to semileptonic decays, such as
decays. The separate definition of strong isospin-breaking effects
and those due to electromagnetism requires a convention. We define and advocate
conventions based on hadronic schemes, in which a chosen set of hadronic
quantities, hadronic masses for example, are set equal in QCD and in QCD+QED.
This is in contrast with schemes which have been largely used to date, in which
the renormalised and quark masses are set equal in QCD and in
QCD+QED in some renormalisation scheme and at some scale .Comment: Presented at the 36th Annual International Symposium on Lattice Field
Theory (Lattice2018), Michigan State University, July 22nd - 28th 201
Scaling of a large-scale simulation of synchronous slow-wave and asynchronous awake-like activity of a cortical model with long-range interconnections
Cortical synapse organization supports a range of dynamic states on multiple
spatial and temporal scales, from synchronous slow wave activity (SWA),
characteristic of deep sleep or anesthesia, to fluctuating, asynchronous
activity during wakefulness (AW). Such dynamic diversity poses a challenge for
producing efficient large-scale simulations that embody realistic metaphors of
short- and long-range synaptic connectivity. In fact, during SWA and AW
different spatial extents of the cortical tissue are active in a given timespan
and at different firing rates, which implies a wide variety of loads of local
computation and communication. A balanced evaluation of simulation performance
and robustness should therefore include tests of a variety of cortical dynamic
states. Here, we demonstrate performance scaling of our proprietary Distributed
and Plastic Spiking Neural Networks (DPSNN) simulation engine in both SWA and
AW for bidimensional grids of neural populations, which reflects the modular
organization of the cortex. We explored networks up to 192x192 modules, each
composed of 1250 integrate-and-fire neurons with spike-frequency adaptation,
and exponentially decaying inter-modular synaptic connectivity with varying
spatial decay constant. For the largest networks the total number of synapses
was over 70 billion. The execution platform included up to 64 dual-socket
nodes, each socket mounting 8 Intel Xeon Haswell processor cores @ 2.40GHz
clock rates. Network initialization time, memory usage, and execution time
showed good scaling performances from 1 to 1024 processes, implemented using
the standard Message Passing Interface (MPI) protocol. We achieved simulation
speeds of between 2.3x10^9 and 4.1x10^9 synaptic events per second for both
cortical states in the explored range of inter-modular interconnections.Comment: 22 pages, 9 figures, 4 table
fB and fBs with maximally twisted Wilson fermions
We present a lattice QCD calculation of the heavy-light decay constants fB and fBs performed with Nf = 2 maximally twisted Wilson fermions, at four values of the lattice spacing. The decay constants have been also computed in the static limit and the results are used to interpolate the observables between the charmand the infinite-mass sectors, thus obtaining the value of the decay constants at the physical b quark mass. Our preliminary results are fB = 191(14)MeV, fBs = 243(14)MeV, fBs/ fB = 1.27(5). They are in good agreement with those obtained with a novel approach, recently proposed by our Collaboration (ETMC), based on the use of suitable ratios having an exactly known static limit
Isospin-breaking corrections to the muon magnetic anomaly in Lattice QCD
In this contribution we present a lattice calculation of the leading-order
electromagnetic and strong isospin-breaking (IB) corrections to the
quark-connected hadronic-vacuum-polarization (HVP) contribution to the
anomalous magnetic moment of the muon. The results are obtained adopting the
RM123 approach in the quenched-QED approximation and using the QCD gauge
configurations generated by the ETM Collaboration with dynamical
quarks, at three values of the lattice spacing (
fm), at several lattice volumes and with pion masses between and
MeV. After the extrapolations to the physical pion mass and to the
continuum and infinite-volume limits the contributions of the light, strange
and charm quarks are respectively equal to , and . At
leading order in and we obtain
, which is currently
the most accurate determination of the IB corrections to .Comment: Invited talk at the 9th International Workshop on Chiral Dynamics
(CD18), Durham, North Carolina (USA), 17-21 September 2018. 11 pages, 4
figure
HVP contribution of the light quarks to the muon including isospin-breaking corrections with Twisted-Mass fermions
We present a preliminary lattice calculation of the leading-order
electromagnetic and strong isospin-breaking corrections to the Hadronic Vacuum
Polarization (HVP) contribution of the light quarks to the anomalous magnetic
moment of the muon. The results are obtained in the quenched-
approximation using the gauge configurations generated by the European
Twisted Mass Collaboration (ETMC) with dynamical quarks, at
three values of the lattice spacing varying from to , at several lattice volumes and with pion masses in the range
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