3,017 research outputs found
Maximum Entropy Analysis of the Spectral Functions in Lattice QCD
First principle calculation of the QCD spectral functions (SPFs) based on the
lattice QCD simulations is reviewed. Special emphasis is placed on the Bayesian
inference theory and the Maximum Entropy Method (MEM), which is a useful tool
to extract SPFs from the imaginary-time correlation functions numerically
obtained by the Monte Carlo method. Three important aspects of MEM are (i) it
does not require a priori assumptions or parametrizations of SPFs, (ii) for
given data, a unique solution is obtained if it exists, and (iii) the
statistical significance of the solution can be quantitatively analyzed.
The ability of MEM is explicitly demonstrated by using mock data as well as
lattice QCD data. When applied to lattice data, MEM correctly reproduces the
low-energy resonances and shows the existence of high-energy continuum in
hadronic correlation functions. This opens up various possibilities for
studying hadronic properties in QCD beyond the conventional way of analyzing
the lattice data. Future problems to be studied by MEM in lattice QCD are also
summarized.Comment: 51 pages, 17 figures, typos corrected, discussions on the boundary
conditions and renormalization constants added. To appear in Progress in
Particle and Nuclear Physics, Vol.4
Hadronic Spectral Functions above the QCD Phase Transition
We extract the spectral functions in the scalar, pseudo-scalar, vector, and
axial vector channels above the deconfinement phase transition temperature (Tc)
using the maximum entropy method (MEM). We use anisotropic lattices, 32^3 * 32,
40, 54, 72, 80, and 96 (corresponding to T = 2.3 Tc --> 0.8 Tc), with the
renormalized anisotropy xi = 4.0 to have enough temporal data points to carry
out the MEM analysis. Our result suggests that the spectral functions continue
to possess non-trivial structures even above Tc and in addition that there is a
qualitative change in the state of the deconfined matter between 1.5 Tc and 2
Tc.Comment: 3 pages, 4 figures, Lattice2002(nonzerot
Quantum knots in Bose-Einstein condensates created by counterdiabatic control
We theoretically study the creation of knot structures in the polar phase of
spin-1 BECs using the counterdiabatic protocol in an unusual fashion. We
provide an analytic solution to the evolution of the external magnetic field
that is used to imprint the knots. As confirmed by our simulations using the
full three-dimensional spin-1 Gross-Pitaevskii equation, our method allows for
the precise control of the Hopf charge as well as the creation time of the
knots. The knots with Hopf charge exceeding unity display multiple nested Hopf
links.Comment: 7 pages, 6 figure
On the zero of the fermion zero mode
We argue that the fermionic zero mode in non-trivial gauge field backgrounds
must have a zero. We demonstrate this explicitly for calorons where its
location is related to a constituent monopole. Furthermore a topological
reasoning for the existence of the zero is given which therefore will be
present for any non-trivial configuration. We propose the use of this property
in particular for lattice simulations in order to uncover the topological
content of a configuration.Comment: 6 pages, 3 figures in 5 part
Designing Robust Unitary Gates: Application to Concatenated Composite Pulse
We propose a simple formalism to design unitary gates robust against given
systematic errors. This formalism generalizes our previous observation [Y.
Kondo and M. Bando, J. Phys. Soc. Jpn. 80, 054002 (2011)] that vanishing
dynamical phase in some composite gates is essential to suppress amplitude
errors. By employing our formalism, we naturally derive a new composite unitary
gate which can be seen as a concatenation of two known composite unitary
operations. The obtained unitary gate has high fidelity over a wider range of
the error strengths compared to existing composite gates.Comment: 7 pages, 4 figures. Major revision: improved presentation in Sec. 3,
references and appendix adde
Fermionic Hopf solitons and Berry's phase in topological surface superconductors
A central theme in many body physics is emergence - new properties arise when
several particles are brought together. Particularly fascinating is the idea
that the quantum statistics may be an emergent property. This was first noted
in the Skyrme model of nuclear matter, where a theory formulated entirely in
terms of a bosonic order parameter field contains fermionic excitations. These
excitations are smooth field textures, and believed to describe neutrons and
protons. We argue that a similar phenomenon occurs in topological insulators
when superconductivity gaps out their surface states. Here, a smooth texture is
naturally described by a three component real vector. Two components describe
superconductivity, while the third captures the band topology. Such a vector
field can assume a 'knotted' configuration in three dimensional space - the
Hopf texture - that cannot smoothly be unwound. Here we show that the Hopf
texture is a fermion. To describe the resulting state, the regular
Landau-Ginzburg theory of superconductivity must be augmented by a topological
Berry phase term. When the Hopf texture is the cheapest fermionic excitation,
striking consequences for tunneling experiments are predicted
Higgs triplets at like-sign linear colliders and neutrino mixing
We study the phenomenology of the type-II seesaw model at a linear e^-e^-
collider. We show that the process e^-e^- \rightarrow alpha^-beta^- (alpha,
beta = e, mu, tau being charged leptons) mediated by a doubly charged scalar is
very sensitive to the neutrino parameters, in particular the absolute neutrino
mass scale and the Majorana CP-violating phases. We identify the regions in
parameter space in which appreciable collider signatures in the channel with
two like-sign muons in the final state are possible. This includes Higgs
triplet masses beyond the reach of the LHC.Comment: 8 pages, 6 figure
Cutoff effects in meson spectral functions
We study the lattice spacing dependence of meson spectral functions
calculated in quenched QCD with domain wall fermions as well as clover Wilson
fermions in quenched and partially-quenched QCD. We conclude that for lattice
spacing GeV all excited states appearing in the spectral functions
are lattice artifacts.Comment: Lattice 2004 (non-zero), 3 pages, 3 figures, uses espcrc2 packag
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