130,937 research outputs found

### Lattice study of the Kink soliton and the zero-mode problem for phi4 in two dimensions

We study the $\lambda\phi^4_{1+1}$ kink solion and the zero-mode contribution
to the Kink soliton mass in regions beyond the semiclassical regime. The
calculations are done in the non-trivial scaling region and where appropriate
the results are compared with the continuum, semiclassical values. We show, as
a function of parameter space, where the zero-mode contributions become
significant.Comment: 10 pages, LaTeX; typos adde

### Vortex Fluctuations in the Critical Casimir Effect of Superfluid and Superconducting Films

Vortex-loop renormalization techniques are used to calculate the magnitude of
the critical Casimir forces in superfluid films. The force is found to become
appreciable when size of the thermal vortex loops is comparable to the film
thickness, and the results for T < Tc are found to match very well with
perturbative renormalization theories that have only been carried out for T >
Tc. When applied to a high-Tc superconducting film connected to a bulk sample,
the Casimir force causes a voltage difference to appear between the film and
bulk, and estimates show that this may be readily measurable.Comment: 4 pages, 5 figures, Revtex 4, typo correctio

### Pion Form Factors at Intermediate Momentum Transfer in a Covariant Approach

We study the pion electromagnetic and $\gamma^* + \pi^0 \to \gamma$
transition form factors at intermediate momentum transfer. We calculate soft,
nonperturbative corrections to the leading perturbative amplitudes which arise
from the $q\bar q$-component of the pion wave function. We work in Minkowski
space and use a Lorentz covariant, gauge-invariant generalized perturbative
integral representation for the $q\bar q$ amplitudes. For the transition form
factor we find relative insensitivity to the detailed nonperturbative structure
of the wavefunction for |q^2|\gsim 10~GeV$^2$, whereas considerable
sensitivity is found for the electromagnetic form factor.Comment: 21 pages, REVTeX 3.0 file, (uuencoded postscript files of 10 figures
appended), ADP-93-216/T13

### Vortex Loop Phase Transitions in Liquid Helium, Cosmic Strings, and High-T_c Superconductors

The distribution of thermally excited vortex loops near a superfluid phase
transition is calculated from a renormalized theory. The number density of
loops with a given perimeter is found to change from exponential decay with
increasing perimeter to algebraic decay as T_c is approached, in agreement with
recent simulations of both cosmic strings and high-T_c superconductors.
Predictions of the value of the exponent of the algebraic decay at T_c and of
critical behavior in the vortex density are confirmed by the simulations,
giving strong support to the vortex-folding model proposed by Shenoy.Comment: Version to appear in Phys. Rev. Lett, with a number of corrections
and addition

### Z' mass limits and the naturalness of supersymmetry

The discovery of a 125 GeV Higgs boson and rising lower bounds on the masses
of superpartners have lead to concerns that supersymmetric models are now fine
tuned. Large stop masses, required for a 125 GeV Higgs, feed into the
electroweak symmetry breaking conditions through renormalisation group
equations forcing one to fine tune these parameters to obtain the correct
electroweak vacuum expectation value. Nonetheless this fine tuning depends
crucially on our assumptions about the supersymmetry breaking scale. At the
same time $U(1)$ extensions provide the most compelling solution to the
$\mu$-problem, which is also a naturalness issue, and allow the tree level
Higgs mass to be raised substantially above $M_Z$. These very well motivated
supersymmetric models predict a new $Z'$ boson which could be discovered at the
LHC and the naturalness of the model requires that the $Z'$ boson mass should
not be too far above the TeV scale. Moreover this fine tuning appears at the
tree level, making it less dependent on assumptions about the supersymmetry
breaking mechanism. Here we study this fine tuning for several $U(1)$
supersymmetric extensions of the Standard Model and compare it to the situation
in the MSSM where the most direct tree level fine tuning can be probed through
chargino mass limits. We show that future LHC $Z'$ searches are extremely
important for challenging the most natural scenarios in these models.Comment: 58 pages, 5 figures; typos corrected, references added; matches
version to be published in Phys. Rev.

### Quick-change absorption column

Column has end caps held in place by springs; prefilled packs of absorbent can be exchanged quickly. Both ends of metal or plastic body tube of size which can hold adequate amount of absorbent are machined to provide seat for perforated plate and groove for its spring retainer ring

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