375 research outputs found
Magnetic permeability of near-critical 3d abelian Higgs model and duality
The three-dimensional abelian Higgs model has been argued to be dual to a
scalar field theory with a global U(1) symmetry. We show that this duality,
together with the scaling and universality hypotheses, implies a scaling law
for the magnetic permeablity chi_m near the line of second order phase
transition: chi_m ~ t^nu, where t is the deviation from the critical line and
nu ~ 0.67 is a critical exponent of the O(2) universality class. We also show
that exactly on the critical lines, the dependence of magnetic induction on
external magnetic field is quadratic, with a proportionality coefficient
depending only on the gauge coupling. These predictions provide a way for
testing the duality conjecture on the lattice in the Coulomb phase and at the
phase transion.Comment: 11 pages; updated references and small changes, published versio
The impact of QCD plasma instabilities on bottom-up thermalization
QCD plasma instabilities, caused by an anisotropic momentum distributions of
the particles in the plasma, are likely to play an important role in
thermalization in heavy ion collisions. We consider plasmas with two different
components of particles, one strongly anisotropic and one isotropic or nearly
isotropic. The isotropic component does not eliminate instabilities but it
decreases their growth rates. We investigate the impact of plasma instabilities
on the first stage of the ``bottom-up'' thermalization scenario in which such a
two-component plasma emerges, and find that even in the case of non-abelian
saturation instabilities qualitatively change the bottom-up picture.Comment: 12 pages, latex, one typo corrected, several minor changes in the
abstract and the text, to appear in JHE
On the Chiral Phase Transition in the Linear Sigma Model
The Cornwall-Jackiw-Tomboulis (CJT) effective action for composite operators
at finite temperature is used to investigate the chiral phase transition within
the framework of the linear sigma model as the low-energy effective model of
quantum chromodynamics (QCD). A new renormalization prescription for the CJT
effective action in the Hartree-Fock (HF) approximation is proposed. A
numerical study, which incorporates both thermal and quantum effect, shows that
in this approximation the phase transition is of first order. However, taking
into account the higher-loop diagrams contribution the order of phase
transition is unchanged.Comment: 12 pages, 4 figure
Thermal production of ultrarelativistic right-handed neutrinos: Complete leading-order results
The thermal production of relativistic right-handed Majorana neutrinos is of
importance for models of thermal leptogenesis in the early Universe.
Right-handed neutrinos can be produced both by 1 2 decay or inverse decay
and by 2 -> 2 scattering processes. In a previous publication, we have studied
the production via 1 2 (inverse) decay processes. There we have shown that
multiple scattering mediated by soft gauge boson exchange also contributes to
the production rate at leading order, and gives a strong enhancement. Here we
complete the leading order calculation by adding 2 -> 2 scattering processes
involving either electroweak gauge bosons or third-generation quarks. We find
that processes with gauge interactions give the most important contributions.
We also obtain a new sum rule for the Hard Thermal Loop resummed fermion
propagator.Comment: 27 pages, 7 figures. Error in the matrix element for the
(subdominant) subprocess with s-channel fermion exchange corrected. This
changes the corresponding phase space integral and the constant c_V.
Numerically it increases the total 2 -> 2 rate by about 2 percent and the
complete rate by about 1 percent. The main results and conclusions are
unaffecte
The stochastic gravitational wave background from turbulence and magnetic fields generated by a first-order phase transition
We analytically derive the spectrum of gravitational waves due to
magneto-hydrodynamical turbulence generated by bubble collisions in a
first-order phase transition. In contrast to previous studies, we take into
account the fact that turbulence and magnetic fields act as sources of
gravitational waves for many Hubble times after the phase transition is
completed. This modifies the gravitational wave spectrum at large scales. We
also model the initial stirring phase preceding the Kolmogorov cascade, while
earlier works assume that the Kolmogorov spectrum sets in instantaneously. The
continuity in time of the source is relevant for a correct determination of the
peak position of the gravitational wave spectrum. We discuss how the results
depend on assumptions about the unequal-time correlation of the source and
motivate a realistic choice for it. Our treatment gives a similar peak
frequency as previous analyses but the amplitude of the signal is reduced due
to the use of a more realistic power spectrum for the magneto-hydrodynamical
turbulence. For a strongly first-order electroweak phase transition, the signal
is observable with the space interferometer LISA.Comment: 46 pages, 17 figures. Replaced with revised version accepted for
publication in JCA
Comparative Study between the Overall Production Time of Digitally Versus Conventionally Produced Indirect Orthodontic Bonding Trays
Objective:The purpose of this study was to compare the production time for indirect digitally and laboratory-produced orthodontic bonding trays.Methods:Orthodontic study casts were used in this study (n=40). The specimens were equally and randomly divided. In the digitally produced indirect bonding tray (DIBT) group (n=20), the brackets were set virtually using the Orthoanalyzer program (3Shape, Copenhagen, Denmark) to produce an indirect bonding tray that was virtually designed and 3D printed using VarseoWax® Splint material with a Varseo S 3D printer (Bego, Bremen, Germany). In the laboratory-produced indirect bonding tray (LIBT) group, the brackets were adhesively bonded to the study casts in the dental laboratory (Danube Private University, Krems, Austria), and a transfer bonding silicone tray was manufactured.Results:The t-test results showed a significant difference between the passive time during the production of DIBTs (153.8±32.8 min) and LIBTs (7 min). However, the active production time was 13.6±0.8 min for DIBTs and 17.7±1.9 min for LIBTs. Every individual process step in both groups was measured in minutes, and statistical analysis was performed.Conclusion:The total production time, including active working and passive non-working time, was higher for DIBTs than for LIBTs. However, the actual active production time for DIBTs was shorter than that for LIBTs. Within the study limitations, the digital planning and production of indirect orthodontic trays can be considered a time-efficient production method
Three Dimensional N=2 Supersymmetry on the Lattice
We show how 3-dimensional, N=2 supersymmetric theories, including super QCD
with matter fields, can be put on the lattice with existing techniques, in a
way which will recover supersymmetry in the small lattice spacing limit.
Residual supersymmetry breaking effects are suppressed in the small lattice
spacing limit by at least one power of the lattice spacing a.Comment: 21 pages, 2 figures, typo corrected, reference adde
Thermal production of relativistic Majorana neutrinos: Strong enhancement by multiple soft scattering
The production rate of heavy Majorana neutrinos is relevant for models of
thermal leptogenesis in the early Universe. In the high temperature limit the
production can proceed via the 1 2 (inverse) decays which are allowed by
the thermal masses. We consider new production mechanisms which are obtained by
including additional soft gauge interactions with the plasma. We show that an
arbitrary number of such interactions gives leading order contributions, and we
sum all of them. The rate turns out to be smooth in the region where the 1
2 processes are kinematically forbidden. At higher temperature it is enhanced
by a factor 3 compared to the 1 2 rate.Comment: 26 pages, 8 figures; added references, added comments on 2 to 2
scattering processes, improved appearance of fig. 8, corrected typos; matches
published versio
Quasiparticle Description of the QCD Plasma, Comparison with Lattice Results at Finite T and Mu
We compare our 2+1 flavor, staggered QCD lattice results with a quasiparticle
picture. We determine the pressure, the energy density, the baryon density, the
speed of sound and the thermal masses as a function of T and . For the
available thermodynamic quantities the difference is a few percent between the
results of the two approaches. We also give the phase diagram on the --T
plane and estimate the critical chemical potential at vanishing temperature.Comment: 13 pages, 10 figure
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