Advances in atomic physics, such as cooling and trapping of atoms and molecules and developments in frequency metrology, have added orders of magnitude to the precision of atom-based clocks and sensors. Applications extend beyond atomic physics and this article reviews using these new techniques to address important challenges in physics and to look for variations in the fundamental constants, search for interactions beyond the standard model of particle physics, and test the principles of general relativity.

Search for New Physics with Atoms and Molecules

Polymerizations of trityl (TMA), diphenylmethyl (DMA) and benzyl (BMA) methacrylates were carried out mainly by n-butyllithium (n-BuLi) and the tacticities of the polymers were studied by NMR spectroscopy. Polymerization of TMA by n-BuLi gave a highly isotactic polymer in toluene as well as in tetrahydrofuran (THF). The polymer obtained in radical polymerization by AIBN catalyst had about 60% isotacticity in triads. From these results the growing-chain-controlled mechanism was proposed to this polymerization. In the polymerization of DMA by n-BuLi a highly isotactic polymer was obtained in toluene at lower temperatures and a highly syndiotactic one in THF. The radical polymerization gave a predominantly syndiotactic polymer. Temperature dependence of the NMR signal-width of the isotactic polymer indicates that the conformational arrangement of the polymer chain in solution is much rigid up to a fairly higher temperature. These results suggest that the growing-chain-controlled mechanism may contribute to some extent to the stereoregulation of DMA in toluene. BMA behaved very similarly to methyl methacrylate in the polymerization by n-BuLi. Probably the same polymerization mechanisms can be applied for both monomers. Polymerization of TMA, DMA and BMA by phenylmagnesium bromide or diethylaluminum diphenylamide was also investigated.

/pdf/stereospecific-polymerization-of-trityl-diphenylmethyl-and-2s90ddcfqm.pdf

Stereospecific Polymerization of Trityl, Diphenylmethyl and Benzyl Methacrylates

The high resolution nuclear magnetic resonance spectroscopy of polymers

A sharp and spatially extended peak in an astrophysical gamma ray spectrum would provide very strong evidence for the existence of dark matter (DM), given that there are no known astrophysical processes that could mimic such a signal From the particle physics perspective, perhaps the simplest explanation for a gamma ray peak is internal bremsstrahlung in DM annihilation through a charged t-channel mediator eta close in mass to the DM particle chi Since DM annihilation to quarks is already tightly constrained in this scenario, we focus here on the leptophilic case We compute the electromagnetic anapole and dipole moments that DM acquires at 1-loop, and we find an interesting enhancement of these moments if the DM particle and the mediator are close in mass We constrain the DM anapole and dipole moments using direct detection data, and then translate these limits into bounds on the DM annihilation cross section Our bounds are highly competitive with those from astrophysical gamma ray searches In the second part of the paper, we derive complementary constraints on internal bremsstrahlung in DM annihilation using LEP mono-photon data, measurements of the anomalous magnetic moments of the electron and the muon, and searches for lepton flavor violation We also comment on the impact of the internal bremsstrahlung scenario on the hyperfine splitting of true muonium

Loopy Constraints on Leptophilic Dark Matter and Internal Bremsstrahlung

Progress in the structure control of polymethacrylates and polyacrylates through stereospecific living polymerization are described. Three types of stereospecific living polymerizations have been developed for methacrylate polymerization: isotactic with t-C4H9MgBr, syndiotactic with ­t-C4H9Li/R3Al, and heterotactic with t-C4H9Li/bis(2,6-di-t-butylphenoxy)methylaluminium [MeAl(ODBP)2]. The last initiator system has been proved effective for monomer-selective living copolymerization of methacrylates. The living nature of these polymerizations allows extensive use for the syntheses of stereoregular block polymers and copolymers, and end-functionalized polymers such as macromonomers. Through stereospecific polymerizations and copolymerizations of macromonomers, comb polymers and graft copolymers with defined stereoregularities in the main chain and side chains could be obtained. Some properties of these stereoregular polymers are also described, including stereocomplex formation and solution viscosity. Stereospecific polymerizations of crotonates leading to diisotactic, diheterotactic and disyndiotactic polymers are also discussed. Supercritical fluid chromatography (SFC) has been proven to be useful for isolating uniform polymers from stereoregular poly(methyl methacrylate)s (PMMAs) with narrow molecular weight distribution. Uniform end-functionalized polymers have been used to construct more elaborate uniform polymer architectures such as stereoblock, star, and comb polymers, and copolymers. The uniform polymers have been proven quite useful for the studies of the relationship between structures and properties such as glass transition temperature, melting temperature and solution viscosity. Particularly interesting is the use of isotactic and syndiotactic uniform PMMAs for the understanding of stereocomplex formation in certain solvents such as acetone. Furthermore, a uniform stereoblock PMMA was found to undergo intramolecular complexation in addition to intermolecular complexation in acetone. Uniform star and comb PMMAs were also prepared and found useful for discussing the effect of branching on the solution viscosity.



© 2000 Society of Chemical Industry

Structurally controlled polymerizations of methacrylates and acrylates

The stereoregularity of poly(methyl acrylate) and poly(methyl acrylate-αd) was determined from the NMR spectra. A method of quantitative determination of stereoregularity of poly(methyl acrylate) proposed in this paper is based on the fact that in the 100 Mc./sec. NMR spectrum the absorption peaks due to methylene protons in syndiotactic configurations overlap absorptions due to only one of two methylene protons in isotactic configurations. The stereostructure of poly(methy1 acrylates) polymerized with anionic catalysts such as Grignard reagents, n-butyllithium, and LiAlH4 is generally richer in isotactic diads than in syndiotactic diads. For example, poly(methyl acrylate) polymerized with phenylmagnesium bromide as catalyst at −20°C. consists of 99% isotactic and 1% syndiotactic diads. In radical polymerization, the isotacticity of poly(methyl acrylate) is independent of polymerization temperature. Poly(methyl acrylates) polymerized with a Ziegler-Natta catalyst consisting of Al(C2H5)2Cl and VCl4 have configurations similar to those polymerized by radical initiators. The stereoregularity of poly(methyl acrylate-α-d) resembled that of poly(methyl acrylate) polymerized under the same conditions.

Stereoregularity of poly(methyl acrylate)

Positronium is an ideal system for precision tests of bound-state quantum electrodynamics (QED). One of the most precisely tested quantities of positronium is the ground-state hyperfine splitting (HFS). Recent progress on theoretical calculation revealed that there was a 16.0 ± 3.5 ppm (4.5 σ) discrepancy between the old experimental value and the theoretical calculation. We performed a new measurement which took into account the positronium thermalization effect for the first time. The result was HFS = 203.3942 ± 0.0016 (stat., 8.0 ppm) ± 0.0013 (syst., 6.4 ppm) GHz, which was consistent with the QED calculation within 1.1 σ, whereas it disfavored the old experimental values by 2.6 σ. It also showed that the positronium thermalization effect on HFS was as large as 10 ± 2 ppm, which was consistent with the discrepancy level within 1.5 σ, which could be the reason of the discrepancy. We are planning to preform a new experiment which uses a slow positron beam and perform HFS measurement in vacuum, instead of using gas as all of the other precision measurements. It will be completely free from material effect on HFS, including the thermalization effect. In this proceeding, summary of our previous work and details of the future new experiment are discussed.

New Precision Measurement of Hyperfine Splitting of Positronium

l-Menthyl methacrylate (l-MnMA) and dl-MnMA and their mixtures were poly merized with benzoyl peroxide (BPO), phenylmagnesium bromide (PhMgBr), and lithium aluminum hydride (LiAlH4), as catalyst. The isotacticity of the polymers of dl-MnMA polymerized with PhMgBr was independent of the polymerization temperature and low. The tacticity of the polymers from the mixtures of l- and dl-MnMA's polymerized with BPO hardly changed with monomer compositions, while that with LiAlH4 showed increase with the increase of l-monomer contents. Thechange of the optical activity of PMnMA's with the stereoregularity is slight as compared with large variation of the tacticity of the polymers. Although both in radical and anionic polymerizations preference of one monomer to another monomer does not occur, in isotactic polymerization with LiAlH4 asymmetric induction of menthyl groups on the main chain configurations takes place. The tacticities of some poly(methacrylic acid esters) polymerized with PhMgBr under similar conditions were compared.

Stereoregularity of poly(methacrylic acid esters)

Stereoregularity of polymethyl acrylate and polyacrylonitrile

Positronium is an ideal system for the research of the quantum electrodynamics (QED) in bound state. The hyperfine splitting (HFS) of positronium, ΔHFS, gives a good test of the bound state calculations and probes new physics beyond the Standard Model. A new method of QED calculations has revealed the discrepancy by 15 ppm (3.9σ) of ΔHFS between the QED prediction and the experimental average. There would be possibility of new physics or common systematic uncertainties in the previous all experiments. We describe a new experiment to reduce possible systematic uncertainties and will provide an independent check of the discrepancy. We are now taking data and the current result of ΔHFS = 203.395 1 ±0.002 4 (stat., 12 ppm) ±0.001 9 (sys., 9.5 ppm) GHz has been obtained so far. A measurement with a precision of O(ppm) is expected within a year.

Precise measurement of positronium hyperfine splitting using the Zeeman effect

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