Isospin splittings of doubly heavy baryons

The SELEX Collaboration has reported a very large isospin splitting of doubly charmed baryons. We show that this effect would imply that the doubly charmed baryons are very compact. One intriguing possibility is that such baryons have a linear geometry Q–q–Q$Q\text{–}q\text{–}Q$ where the light quark q oscillates between the two heavy quarks Q  , analogous to a linear molecule such as carbon dioxide. However, using conventional arguments, the size of a heavy-light hadron is expected to be around 0.5 fm, much larger than the size needed to explain the observed large isospin splitting. Assuming the distance between two heavy quarks is much smaller than that between the light quark and a heavy one, the doubly heavy baryons are related to the heavy mesons via heavy quark–diquark symmetry. Based on this symmetry, we predict the isospin splittings for doubly heavy baryons including Ξ_cc${\Xi }_{cc}$, Ξ_bb${\Xi }_{bb}$ and Ξ_bc${\Xi }_{bc}$. The prediction for the Ξ_cc${\Xi }_{cc}$ is much smaller than the SELEX value. On the other hand, the Ξ_bb${\Xi }_{bb}$ baryons are predicted to have an isospin splitting as large as (6.3±1.7) MeV$(6.3\pm 1.7)\text{MeV}$. An experimental study of doubly bottomed baryons is therefore very important to better understand the structure of baryons with heavy quarks.     

High-energy QCD asymptotic behavior of photon-photon collisions

Complex quasienergy and level width are calculated for a weakly bound atomic state in an intense circularly polarized monochromatic laser field using the method suggested by Zel’dovich for the regularization of divergent integrals with the Gamow wave function. It is demonstrated that this method converges, and the conditions for its applicability are indicated. These results are used to discuss the accuracy of the semiclassical approximation in the problems of ionization theory.     

Green microfluidic devices made of corn proteins

An alternative green microfluidic device made of zein, a prolamin of corn, can be utilized as a disposable environmentally friendly microchip especially in agriculture applications. Using standard soft lithography and stereo lithography techniques, we fabricated thin zein films with microfluidic chambers and channels. These were bonded to both a glass slide and another zein film. The zein film with microfluidic features bonds irreversibly with other surfaces by vapor-deposition of ethanol to create an adhesive layer resulting in very little or no trapped air and small shape distortion. Zein-zein and zein-glass microfluidic devices demonstrated sufficient strength to facilitate fluid flow in a complex microfluidic design that showed no leakage under high hydraulic pressure. Zein-glass microfluidic devices with serpentine mixing design showed successful fluid manipulation as a concentration gradient of Rhodamine B solution was generated. The ease of fabrication and bonding and the flexibility and moldability of zein offer attractive possibilities for microfluidic device design and manufacturing. These devices can include several unit operations with mixing being one of the most commonly used. The zein-based microfluidic devices, made entirely from a biopolymer from agricultural origin, offer alternative environmentally friendly material choices that are less dependent on limited petroleum based polymer resources.     

The universal torsion-free image of a group

We show that the universal torsion free homomorphic image of any group given by a sufficiently ‘small’ presentation is locally indicable, and give an application to a conjecture of Levin about equations over torsion free groups. Supported by SERC Visiting Fellowship GR/F 97355.     

<Emphasis Type="Italic">N</Emphasis>-arachidonoyl glycine,an abundant endogenous lipid,potently drives directed cellular migration through GPR18, the putative abnormal cannabidiol receptor

Background  

Microglia provide continuous immune surveillance of the CNS and upon activation rapidly change phenotype to express receptors that respond to chemoattractants during CNS damage or infection. These activated microglia undergo directed migration towards affected tissue. Importantly, the molecular species of chemoattractant encountered determines if microglia respond with pro- or anti-inflammatory behaviour, yet the signaling molecules that trigger migration remain poorly understood. The endogenous cannabinoid system regulates microglial migration via CB₂ receptors and an as yet unidentified GPCR termed the 'abnormal cannabidiol' (Abn-CBD) receptor. Abn-CBD is a synthetic isomer of the phytocannabinoid cannabidiol (CBD) and is inactive at CB₁ or CB₂ receptors, but functions as a selective agonist at this G_i/o-coupled GPCR. N-arachidonoyl glycine (NAGly) is an endogenous metabolite of the endocannabinoid anandamide and acts as an efficacious agonist at GPR18. Here, we investigate the relationship between NAGly, Abn-CBD, the unidentified 'Abn-CBD' receptor, GPR18, and BV-2 microglial migration.     

Interferometric optical signal-to-noise ratio measurements of telecom signals with degraded extinction ratio

We measure full interferograms of telecom signals impaired by noise and investigate their applicability to in-band optical signal-to-noise ratio (OSNR) monitoring in practical systems. We experimentally establish that the dependence of overall shape of the interferogram on a signal's extinction ratio (ER) is strong but not unique. As the ER is being degraded the interferogram evolves in two distinct ways depending on the modulation conditions. The resulting ambiguity in the interferogram shape prevents OSNR measurements on completely unknown signals and necessitates a calibration for each modulator condition. With appropriate calibration, we experimentally demonstrate reliable OSNR measurements in the 5 to 25 dB range for 42.8 Gb/s nonreturn-to-zero, return-to-zero, and carrier-suppressed return-to-zero on-off-keyed signals.     

Light-Front Holography,Color Confinement,and Supersymmetric Features of QCD

Light-Front Quantization—Dirac’s “Front Form”—provides a physical, frame-independent formalism for hadron dynamics and structure. Observables such as structure functions, transverse momentum distributions, and distribution amplitudes are defined from the hadronic light-front wavefunctions. One obtains new insights into the hadronic spectrum, light-front wavefunctions, and the functional form of the QCD running coupling in the nonperturbative domain using light-front holography—the duality between the front form and AdS₅, the space of isometries of the conformal group. In addition, superconformal algebra leads to remarkable supersymmetric relations between mesons and baryons of the same parity. The mass scale \({\kappa}\) underlying confinement and hadron masses can be connected to the parameter \({\Lambda_{\overline {MS}}}\) in the QCD running coupling by matching the nonperturbative dynamics, as described by the effective conformal theory mapped to the light-front and its embedding in AdS space, to the perturbative QCD regime. The result is an effective coupling defined at all momenta. This matching of the high and low momentum transfer regimes determines a scale Q₀ which sets the interface between perturbative and nonperturbative hadron dynamics. The use of Q₀ to resolve the factorization scale uncertainty for structure functions and distribution amplitudes, in combination with the principle of maximal conformality for setting the renormalization scales, can greatly improve the precision of perturbative QCD predictions for collider phenomenology. The absence of vacuum excitations of the causal, frame-independent front form vacuum has important consequences for the cosmological constant. I also discuss evidence that the antishadowing of nuclear structure functions is non-universal; i.e., flavor dependent, and why shadowing and antishadowing phenomena may be incompatible with the momentum and other sum rules for nuclear parton distribution functions.     

The mass renormalization of nonperturbative light-front Hamiltonian theory: an illustration using truncated, Pauli-Villars-regulated Yukawa interactions

We obtain analytic, nonperturbative, approximate solutions of Yukawa theory in the one-fermion sector using light-front quantization. The theory is regulated in the ultraviolet by the introduction of heavy Pauli-Villars scalar and fermion fields, each with negative norm. In order to obtain a directly soluble problem, fermion-pair creation and annihilation are neglected, and the number of bosonic constituents is limited to one of either type. We discuss some of the features of the wave function of the eigensolution, including its endpoint behavior and spin and orbital angular momentum content. The limit of infinite Pauli-Villars mass receives special scrutiny.