10,238 research outputs found
The Hubbard model on a complete graph: Exact Analytical results
We derive the analytical expression of the ground state of the Hubbard model
with unconstrained hopping at half filling and for arbitrary lattice sites.Comment: Email:[email protected]
Extraction of and from experimental decay rates using lattice QCD form factors
We present a determination of the Cabibbo-Kobayashi-Maskawa matrix elements
and obtained by combining the momentum dependence of the
semileptonic vector form factors and , recently determined from lattice QCD simulations, with the
differential rates measured for the semileptonic and decays. Our analysis is based on the results for the
semileptonic form factors produced by the European Twisted Mass Collaboration
with flavors of dynamical quarks in the whole range of values
of the squared 4-momentum transfer accessible in the experiments. The
statistical and systematic correlations between the lattice data as well as
those present in the experimental data are properly taken into account. With
respect to the standard procedure based on the use of only the vector form
factor at zero 4-momentum transfer, we obtain more precise and consistent
results: and . The
second-row CKM unitarity is fulfilled within the current uncertainties:
. Moreover, using for the
first time hadronic inputs determined from first principles, we have calculated
the ratio of the semileptonic decay rates into muons and
electrons, which represent a test of lepton universality within the SM,
obtaining in the isospin-symmetric limit of QCD: and .Comment: 8 pages, 2 figures, 8 tables. Version to appear in EPJ
Domain walls and bubble-droplets in immiscible binary Bose gases
The existence and stability of domain walls (DWs) and bubble-droplet (BD)
states in binary mixtures of quasi-one-dimensional ultracold Bose gases with
inter- and intra-species repulsive interactions is considered. Previously, DWs
were studied by means of coupled systems of Gross-Pitaevskii equations (GPEs)
with cubic terms, which model immiscible binary Bose-Einstein condensates
(BECs). We address immiscible BECs with two- and three-body repulsive
interactions, as well as binary Tonks--Girardeau (TG) gases, using systems of
GPEs with cubic and quintic nonlinearities for the binary BEC, and coupled
nonlinear Schr\"{o}dinger equations with quintic terms for the TG gases. Exact
DW\ solutions are found for the symmetric BEC mixture, with equal intra-species
scattering lengths. Stable asymmetric DWs in the BEC mixtures with dissimilar
interactions in the two components, as well as of symmetric and asymmetric DWs
in the binary TG gas, are found by means of numerical and approximate
analytical methods. In the BEC system, DWs can be easily put in motion by phase
imprinting. Combining a DW and anti-DW on a ring, we construct BD states for
both the BEC and TG models. These consist of a dark soliton in one component
(the "bubble"), and a bright soliton (the "droplet") in the other. In the BEC
system, these composite states are mobile too.Comment: Phys. Rev. A, in pres
Quantum-tunneling dynamics of a spin-polarized Fermi gas in a double-well potential
We study the exact dynamics of a one-dimensional spin-polarized gas of
fermions in a double-well potential at zero and finite temperature. Despite the
system is made of non-interacting fermions, its dynamics can be quite complex,
showing strongly aperiodic spatio-temporal patterns during the tunneling. The
extension of these results to the case of mixtures of spin-polarized fermions
in interaction with self-trapped Bose-Einstein condensates (BECs) at zero
temperature is considered as well. In this case we show that the fermionic
dynamics remains qualitatively similar to the one observed in absence of BEC
but with the Rabi frequencies of fermionic excited states explicitly depending
on the number of bosons and on the boson-fermion interaction strength. From
this, the possibility to control quantum fermionic dynamics by means of
Feshbach resonances is suggested.Comment: Accepted for publication in Phys. Rev.
Hypercubic effects in semileptonic decays of heavy mesons, toward , with Twisted fermions
We present a preliminary study toward a lattice determination of the vector
and scalar form factors of the semileptonic decays. We
compute the form factors relative to the transition between heavy-light
pseudoscalar mesons, with masses above the physical D-mass, and the pion. We
simulate heavy-quark masses in the range .
Lorentz symmetry breaking due to hypercubic effects is clearly observed in the
data, and included in the decomposition of the current matrix elements in terms
of additional form factors. We discuss the size of this breaking as the
parent-meson mass increases. Our analysis is based on the gauge configurations
produced by the European Twisted Mass Collaboration with
flavors of dynamical quarks at three different values of the lattice spacing
and with pion masses as small as MeV.Comment: 7 pages, 5 figures; contribution to the XXXVI International Symposium
on Lattice Field Theory (LATTICE2018), East Lansing (Michigan State
University, USA), July 22-28, 201
Landau-Zener Tunneling of Bose-Einstein Condensates in an Optical Lattice
A theory of the non-symmetric Landau-Zener tunneling of Bose-Einstein
condensates in deep optical lattices is presented. It is shown that periodic
exchange of matter between the bands is described by a set of linearly coupled
nonlinear Schr\"{o}dinger equations. The key role of the modulational
instability in rendering the inter-band transitions irreversible is
highlighted.Comment: 4 pages, 3 figure
Il dovere di fedelt\ue0 tra simbolismo costituzionale e patriottismo repubblicano
Nel saggio si analizza il dovere di fedelt\ue0 alla Repubblica, sia dal punto di vista dell'aspetto simbolico che tale dovere riveste nell'ambito dell'ordinamento costituzionale, sia dal punto di vista della categoria dei doveri costituzionali. Dopo una disamina delle principali opinioni dottrinali sulle predette questioni, si prospetta una configurazione volta a rafforzare ed estendere il valore deontologico di tale dovere
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