Prospects of searches for long-lived charged particles with MoEDAL

We study the prospects of searches for exotic long-lived particles with the MoEDAL detector at the LHC, assuming the integrated luminosity of 30 fb$^{-1}$ that is expected at the end of Run 3. MoEDAL incorporates nuclear track detectors deployed a few metres away from the interaction point, which are sensitive to any highly-ionizing particles. Hence MoEDAL is able to detect singly- or doubly-charged particles with low velocities $\beta < 0.15$ or $< 0.3$, respectively, and lifetimes larger than ${\cal O}(1) \,{\rm m}/c$. We examine the MoEDAL sensitivity to various singly-charged supersymmetric particles with long lifetimes and to several types of doubly-charged long-lived particles with different spins and SU(2) charges. We compare the prospective MoEDAL mass reaches to current limits from ATLAS and CMS, which involve auxiliary analysis assumptions. MoEDAL searches for doubly-charged fermions are particularly competitive.Comment: 19 pages, 5 figure

Nonadiabatic transitions in a Stark decelerator

In a Stark decelerator, polar molecules are slowed down and focussed by an inhomogeneous electric field which switches between two configurations. For the decelerator to work, it is essential that the molecules follow the changing electric field adiabatically. When the decelerator switches from one configuration to the other, the electric field changes in magnitude and direction, and this can cause molecules to change state. In places where the field is weak, the rotation of the electric field vector during the switch may be too rapid for the molecules to maintain their orientation relative to the field. Molecules that are at these places when the field switches may be lost from the decelerator as they are transferred into states that are not focussed. We calculate the probability of nonadiabatic transitions as a function of position in the periodic decelerator structure and find that for the decelerated group of molecules the loss is typically small, while for the un-decelerated group of molecules the loss can be very high. This loss can be eliminated using a bias field to ensure that the electric field magnitude is always large enough. We demonstrate our findings by comparing the results of experiments and simulations for the Stark deceleration of LiH and CaF molecules. We present a simple method for calculating the transition probabilities which can easily be applied to other molecules of interest.Comment: 12 pages, 9 figures, minor revisions following referee suggestion

Radio Properties of z>4 Optically-Selected Quasars

We report on two programs to address differential evolution between the radio-loud and radio-quiet quasar populations at high (z>4) redshift. Both programs entail studying the radio properties of optically-selected quasars. First, we have observed 32 optically-selected, high-redshift (z>4) quasars with the VLA at 6 cm (5 GHz). These sources comprise a statistically complete and well-understood sample. We detect four quasars above our 3-sigma limit of ~0.15 mJy, which is sufficiently sensitive to detect all radio-loud quasars at the probed redshift range. Second, we have correlated 134 z>4 quasars, comprising all such sources that we are aware of as of mid-1999, with FIRST and NVSS. These two recent 1.4 GHz VLA sky surveys reach 3-sigma limits of approximately 0.6 mJy and 1.4 mJy respectively. We identify a total of 15 z>4 quasars, of which six were not previously known to be radio-loud. The depth of these surveys does not reach the radio-loud/radio-quiet demarcation luminosity density (L(1.4 GHz) = 10^32.5 h(50)^(-2) ergs/s/Hz) at the redshift range considered; this correlation therefore only provides a lower limit to the radio-loud fraction of quasars at high-redshift. The two programs together identify eight new radio-loud quasars at z>4, a significant increase over the seven currently in the published literature. We find no evidence for radio-loud fraction depending on optical luminosity for -25 > M_B > -28 at z~2, or for -26>M_B>-28 at z>4. Our results also show no evolution in the radio-loud fraction between z~2 and z>4 (-26>M_B>-28).Comment: 19 pages, 7 figures; to appear in The Astronomical Journal (April 2000

Stark deceleration of CaF molecules in strong- and weak-field seeking states

We report the Stark deceleration of CaF molecules in the strong-field seeking ground state and in a weak-field seeking component of a rotationally-excited state. We use two types of decelerator, a conventional Stark decelerator for the weak-field seekers, and an alternating gradient decelerator for the strong-field seekers, and we compare their relative merits. We also consider the application of laser cooling to increase the phase-space density of decelerated molecules.Comment: 10 pages, 8 figure

A 43-GHz Survey in the ELAIS N2 Area

We describe a survey in the ELAIS N2 region with the VLA at 43.4 GHz, carried out with 1627 independent snapshot observations in D-configuration and covering about 0.5 square degrees. One certain source is detected, a previously-catalogued flat-spectrum QSO at z=2.2. A few (<5) other sources may be present at about the 3sigma level, as determined from positions of source-like deflections coinciding with blue stellar objects, or with sources from lower-frequency surveys. Independently we show how all the source-like detections identified in the data can be used with a maximum-likelihood technique to constrain the 43-GHz source counts at a level of ~7 mJy. Previous estimates of the counts at 43 GHz, based on lower-frequency counts and spectral measurements, are consistent with these constraints, although the present results are suggestive of somewhat higher surface densities at the 7 mJy level. They do not provide direct evidence of intrusion of a previously unknown source population, although the several candidate sources need examination before such a population can be ruled out.Comment: 13 pages, 11 figures, 1 table; accepted for publication in Mon. Not R. Astr. So

Aromatic oligoesters as novel helix mimetic scaffolds

The design, synthesis, and conformational analysis of a novel aromatic oligoester helix mimetic scaffold is reported. A range of amino acid-type side-chain functionality can be readily incorporated into monomer building blocks over three facile synthetic steps. Analysis of representative dimers revealed a stable conformer capable of effective mimicry of a canonical α-helix and the scaffold was found to be surprisingly stable to degradation in aqueous solutions at acidic and neutral pH

The final two redshifts for radio sources from the equatorial BRL sample

Best, Rottgering and Lehnert (1999, 2000a) defined a new sample of powerful radio sources from the Molonglo Reference Catalogue, for which redshifts were compiled or measured for 177 of the 178 objects. For the final object, MRC1059-010 (3C249), the host galaxy is here identified using near-infrared imaging, and the redshift is determined from VLT spectroscopy. For one other object in the sample, MRC0320+053 (4C05.14), the literature redshift has been questioned: new spectroscopic observations of this object are presented, deriving a corrected redshift. With these two results, the spectroscopic completeness of this sample is now 100%. New redshifts are also presented for PKS0742+10 from the Wall & Peacock 2.7 GHz catalogue, and PKS1336+003 from the Parkes Selected Regions. PKS0742+10 shows a strong neutral hydrogen absorption feature in its Lyman-alpha emission profile.Comment: 4 pages. LaTeX. Accepted for publication in MNRA

Semiclassical time--dependent propagation in three dimensions: How accurate is it for a Coulomb potential?

A unified semiclassical time propagator is used to calculate the semiclassical time-correlation function in three cartesian dimensions for a particle moving in an attractive Coulomb potential. It is demonstrated that under these conditions the singularity of the potential does not cause any difficulties and the Coulomb interaction can be treated as any other non-singular potential. Moreover, by virtue of our three-dimensional calculation, we can explain the discrepancies between previous semiclassical and quantum results obtained for the one-dimensional radial Coulomb problem.Comment: 8 pages, 4 figures (EPS

Canonical Melnikov theory for diffeomorphisms

We study perturbations of diffeomorphisms that have a saddle connection between a pair of normally hyperbolic invariant manifolds. We develop a first-order deformation calculus for invariant manifolds and show that a generalized Melnikov function or Melnikov displacement can be written in a canonical way. This function is defined to be a section of the normal bundle of the saddle connection. We show how our definition reproduces the classical methods of Poincar\'{e} and Melnikov and specializes to methods previously used for exact symplectic and volume-preserving maps. We use the method to detect the transverse intersection of stable and unstable manifolds and relate this intersection to the set of zeros of the Melnikov displacement.Comment: laTeX, 31 pages, 3 figure

Phase Transitions of Single Semi-stiff Polymer Chains

We study numerically a lattice model of semiflexible homopolymers with nearest neighbor attraction and energetic preference for straight joints between bonded monomers. For this we use a new algorithm, the "Pruned-Enriched Rosenbluth Method" (PERM). It is very efficient both for relatively open configurations at high temperatures and for compact and frozen-in low-T states. This allows us to study in detail the phase diagram as a function of nn-attraction epsilon and stiffness x. It shows a theta-collapse line with a transition from open coils to molten compact globules (large epsilon) and a freezing transition toward a state with orientational global order (large stiffness x). Qualitatively this is similar to a recently studied mean field theory (Doniach et al. (1996), J. Chem. Phys. 105, 1601), but there are important differences. In contrast to the mean field theory, the theta-temperature increases with stiffness x. The freezing temperature increases even faster, and reaches the theta-line at a finite value of x. For even stiffer chains, the freezing transition takes place directly without the formation of an intermediate globule state. Although being in contrast with mean filed theory, the latter has been conjectured already by Doniach et al. on the basis of low statistics Monte Carlo simulations. Finally, we discuss the relevance of the present model as a very crude model for protein folding.Comment: 11 pages, Latex, 8 figure