451 research outputs found
Hadron masses in QCD with one quark flavour
One-flavour QCD - a gauge theory with SU(3) colour gauge group and a fermion
in the fundamental representation - is studied by Monte Carlo simulations. The
mass spectrum of hadronic bound states is investigated in a volume with
extensions of L ~ 4.4r_0 (~2.2fm) at two different lattice spacings: a ~
0.37r_0 (~0.19fm) and a ~ 0.27r_0 (~0.13fm). The lattice action is Symanzik
tree-level-improved Wilson action for the gauge field and (unimproved) Wilson
action for the fermion.Comment: 21 pages, 4 figures; further references adde
Structure of penetrable-rod fluids: Exact properties and comparison between Monte Carlo simulations and two analytic theories
Bounded potentials are good models to represent the effective two-body
interaction in some colloidal systems, such as dilute solutions of polymer
chains in good solvents. The simplest bounded potential is that of penetrable
spheres, which takes a positive finite value if the two spheres are overlapped,
being 0 otherwise. Even in the one-dimensional case, the penetrable-rod model
is far from trivial, since interactions are not restricted to nearest neighbors
and so its exact solution is not known. In this paper we first derive the exact
correlation functions of penetrable-rod fluids to second order in density at
any temperature, as well as in the high-temperature and zero-temperature limits
at any density. Next, two simple analytic theories are constructed: a
high-temperature approximation based on the exact asymptotic behavior in the
limit and a low-temperature approximation inspired by the exact
result in the opposite limit . Finally, we perform Monte Carlo
simulations for a wide range of temperatures and densities to assess the
validity of both theories. It is found that they complement each other quite
well, exhibiting a good agreement with the simulation data within their
respective domains of applicability and becoming practically equivalent on the
borderline of those domains. A perspective on the extension of both approaches
to the more realistic three-dimensional case is provided.Comment: 19 pages, 11 figures, 4 tables: v2: minor changes; published final
versio
Monte Carlo simulation of SU(2) Yang-Mills theory with light gluinos
In a numerical Monte Carlo simulation of SU(2) Yang-Mills theory with light
dynamical gluinos the low energy features of the dynamics as confinement and
bound state mass spectrum are investigated. The motivation is supersymmetry at
vanishing gluino mass. The performance of the applied two-step multi-bosonic
dynamical fermion algorithm is discussed.Comment: latex, 48 pages, 16 figures with epsfi
Gribov no-pole condition, Zwanziger horizon function, Kugo-Ojima confinement criterion, boundary conditions, BRST breaking and all that
We aim to offer a kind of unifying view on two popular topics in the studies
of nonperturbative aspects of Yang-Mills theories in the Landau gauge: the
so-called Gribov-Zwanziger approach and the Kugo-Ojima confinement criterion.
Borrowing results from statistical thermodynamics, we show that imposing the
Kugo-Ojima confinement criterion as a boundary condition leads to a modified
yet renormalizable partition function. We verify that the resulting partition
function is equivalent with the one obtained by Gribov and Zwanziger, which
restricts the domain of integration in the path integral within the first
Gribov horizon. The construction of an action implementing a boundary condition
allows one to discuss the symmetries of the system in the presence of the
boundary. In particular, the conventional BRST symmetry is softly broken.Comment: 5 pages. v2 matches version to appear in PhysRevD (RC
The supersymmetric Ward identities on the lattice
Supersymmetric (SUSY) Ward identities are considered for the N=1 SU(2) SUSY
Yang Mills theory discretized on the lattice with Wilson fermions (gluinos).
They are used in order to compute non-perturbatively a subtracted gluino mass
and the mixing coefficient of the SUSY current. The computations were performed
at gauge coupling =2.3 and hopping parameter =0.1925, 0.194,
0.1955 using the two-step multi-bosonic dynamical-fermion algorithm. Our
results are consistent with a scenario where the Ward identities are satisfied
up to O(a) effects. The vanishing of the gluino mass occurs at a value of the
hopping parameter which is not fully consistent with the estimate based on the
chiral phase transition. This suggests that, although SUSY restoration appears
to occur close to the continuum limit of the lattice theory, the results are
still affected by significant systematic effects.Comment: 34 pages, 7 figures. Typo corrected, last sentence reformulated,
reference added. To appear in Eur. Phys. J.
Mass Spectrum and Bounds on the Couplings in Yukawa Models With Mirror-Fermions
The symmetric Yukawa model with mirror-fermions
in the limit where the mirror-fermion is decoupled is studied both analytically
and numerically. The bare scalar self-coupling is fixed at zero and
infinity. The phase structure is explored and the relevant phase transition is
found to be consistent with a second order one. The fermionic mass spectrum
close to that transition is discussed and a first non-perturbative estimate of
the influence of fermions on the upper and lower bounds on the renormalized
scalar self-coupling is given. Numerical results are confronted with
perturbative predictions.Comment: 7 (Latex) page
DIGITAL CULTURAL HERITAGE MEETS DIGITAL HUMANITIES
Digital Cultural Heritage and Digital Humanities are, historically seen, in focus of different communities as well as approaching different research topics and - from an organizational point of view - departments. However, are they that different? The idea of this joint article involving digital humanists and heritage researchers is to examine communities, concepts and research applications as well as shared challenges. Beyond a collection of problem-centred essays this is intended to initiate a fruitful discussion about commonalities and differences between both scholarly fields as well as to assess to which extent they are two sides of the same medal
Bubble formation in potential
Scalar field theory with an asymmetric potential is studied at zero
temperature and high-temperature for potential. The equations of
motion are solved numerically to obtain O(4) spherical symmetric and O(3)
cylindrical symmetric bounce solutions. These solutions control the rates for
tunneling from the false vacuum to the true vacuum by bubble formation. The
range of validity of the thin-wall approximation (TWA) is investigated. An
analytical solution for the bounce is presented, which reproduces the action in
the thin-wall as well as the thick-wall limits.Comment: 22 pag
On a new definition of quantum entropy
It is proved here that, as a consequence of the unitary quantum evolution,
the expectation value of a properly defined quantum entropy operator (as
opposed to the non-evolving von Neumann entropy) can only increase during non
adiabatic transformations and remains constant during adiabatic ones. Thus
Clausius formulation of the second law is established as a theorem in quantum
mechanics, in a way that is equivalent to the previously established
formulation in terms of minimal work principle [A. E. Allahverdyan and T. M.
Nieuwenhuizen, Phys. Rev. E 71, 046107 (2005)]. The corresponding Quantum
Mechanical Principle of Entropy Increase is then illustrated with an exactly
solvable example, namely the driven harmonic oscillator. Attention is paid to
both microcanonical and canonical initial condition. The results are compared
to their classical counterparts.Comment: 4 pages, 3 figure
Abstract: Structural changes of the electricity market:Regulatory approaches under increasing shares of renewables
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