On the non-vanishing of the Collins mechanism for single spin asymmetries

The Collins mechanism provides a non-perturbative explanation for the large single spin asymmetries found in hard semi-inclusive reactions involving a transversely polarized nucleon. However, there are seemingly convincing reasons to suspect that the mechanism vanishes, and indeed it does vanish in the naive parton model where a quark is regarded as an essentially 'free' particle. We give an intuitive analysis which highlights the difference between the naive picture and the realistic one, and shows how the Collins mechanism arises when the quark is described as an off-shell particle by a field in interaction. A typographical error is corrected in this version.Comment: 15 pages, 2 figure

General U(N) gauge transformations in the realm of covariant Hamiltonian field theory

A consistent, local coordinate formulation of covariant Hamiltonian field theory is presented. While the covariant canonical field equations are equivalent to the Euler-Lagrange field equations, the covariant canonical transformation theory offers more general means for defining mappings that preserve the action functional - and hence the form of the field equations - than the usual Lagrangian description. Similar to the well-known canonical transformation theory of point dynamics, the canonical transformation rules for fields are derived from generating functions. As an interesting example, we work out the generating function of type F_2 of a general local U(N) gauge transformation and thus derive the most general form of a Hamiltonian density that is form-invariant under local U(N) gauge transformations.Comment: 36 pages, Symposium on Exciting Physics: Quarks and gluons/atomic nuclei/biological systems/networks, Makutsi Safari Farm, South Africa, 13-20 November 2011; Exciting Interdisciplinary Physics, Walter Greiner, Ed., FIAS Interdisciplinary Science Series, Springer International Publishing Switzerland, 201

Ringing the Randall-Sundrum braneworld: metastable gravity wave bound states

In the Randall-Sundrum scenario, our universe is a 4-dimensional `brane' living in a 5-dimensional bulk spacetime. By studying the scattering of bulk gravity waves, we show that this brane rings with a characteristic set of complex quasinormal frequencies, much like a black hole. To a bulk observer these modes are interpreted as metastable gravity wave bound states, while a brane observer views them as a discrete spectrum of decaying massive gravitons. Potential implications of these scattering resonances are discussed.Comment: References and misc. comments added. "Implications" section expanded. REVTeX4, 5 pages, 4 figure

Spherically symmetric spacetimes in f(R) gravity theories

We study both analytically and numerically the gravitational fields of stars in f(R) gravity theories. We derive the generalized Tolman-Oppenheimer-Volkov equations for these theories and show that in metric f(R) models the Parameterized Post-Newtonian parameter $\gamma_{\rm PPN} = 1/2$ is a robust outcome for a large class of boundary conditions set at the center of the star. This result is also unchanged by introduction of dark matter in the Solar System. We find also a class of solutions with $\gamma_{\rm PPN} \approx 1$ in the metric $f(R)=R-\mu^4/R$ model, but these solutions turn out to be unstable and decay in time. On the other hand, the Palatini version of the theory is found to satisfy the Solar System constraints. We also consider compact stars in the Palatini formalism, and show that these models are not inconsistent with polytropic equations of state. Finally, we comment on the equivalence between f(R) gravity and scalar-tensor theories and show that many interesting Palatini f(R) gravity models can not be understood as a limiting case of a Jordan-Brans-Dicke theory with $\omega \to -3/2$.Comment: Published version, 12 pages, 7 figure

WKB approximation for multi-channel barrier penetrability

Using a method of local transmission matrix, we generalize the well-known WKB formula for a barrier penetrability to multi-channel systems. We compare the WKB penetrability with a solution of the coupled-channels equations, and show that the WKB formula works well at energies well below the lowest adiabatic barrier. We also discuss the eigen-channel approach to a multi-channel tunneling, which may improve the performance of the WKB formula near and above the barrier.Comment: 15 pages, 4 eps figure

Baryon Fields with U_L(3) \times U_R(3) Chiral Symmetry: Axial Currents of Nucleons and Hyperons

We use the conventional F and D octet and decimet generator matrices to reformulate chiral properties of local (non-derivative) and one-derivative non-local fields of baryons consisting of three quarks with flavor SU(3) symmetry that were expressed in SU(3) tensor form in Ref. [12]. We show explicitly the chiral transformations of the [(6,3)\oplus(3,6)] chiral multiplet in the "SU(3) particle basis", for the first time to our knowledge, as well as those of the (3,\bar{3}) \oplus (\bar{3}, 3), (8,1) \oplus (1,8) multiplets, which have been recorded before in Refs. [4,5]. We derive the vector and axial-vector Noether currents, and show explicitly that their zeroth (charge-like) components close the SU_L(3) \times SU_R(3) chiral algebra. We use these results to study the effects of mixing of (three-quark) chiral multiplets on the axial current matrix elements of hyperons and nucleons. We show, in particular, that there is a strong correlation, indeed a definite relation between the flavor-singlet (i.e. the zeroth), the isovector (the third) and the eighth flavor component of the axial current, which is in decent agreement with the measured ones.Comment: one typo correction, and accepted by PR

Time-dependent approach to many-particle tunneling in one-dimension

Employing the time-dependent approach, we investigate a quantum tunneling decay of many-particle systems. We apply it to a one-dimensional three-body problem with a heavy core nucleus and two valence protons. We calculate the decay width for two-proton emission from the survival probability, which well obeys the exponential decay-law after a sufficient time. The effect of the correlation between the two emitted protons is also studied by observing the time evolution of the two-particle density distribution. It is shown that the pairing correlation significantly enhances the probability for the simultaneous diproton decay.Comment: 9 pages, 10 eps figure

Covariant Hamiltonian Field Theory

A consistent, local coordinate formulation of covariant Hamiltonian field theory is presented. Whereas the covariant canonical field equations are equivalent to the Euler-Lagrange field equations, the covariant canonical transformation theory offers more general means for defining mappings that preserve the form of the field equations than the usual Lagrangian description. It is proved that Poisson brackets, Lagrange brackets, and canonical 2-forms exist that are invariant under canonical transformations of the fields. The technique to derive transformation rules for the fields from generating functions is demonstrated by means of various examples. In particular, it is shown that the infinitesimal canonical transformation furnishes the most general form of Noether's theorem. We furthermore specify the generating function of an infinitesimal space-time step that conforms to the field equations.Comment: 93 pages, no figure

Giant Stark effect in the emission of single semiconductor quantum dots

We study the quantum-confined Stark effect in single InAs/GaAs quantum dots embedded within a AlGaAs/GaAs/AlGaAs quantum well. By significantly increasing the barrier height we can observe emission from a dot at electric fields of -500 kV/cm, leading to Stark shifts of up to 25 meV. Our results suggest this technique may enable future applications that require self-assembled dots with transitions at the same energy

A T-odd observable sensitive to CP violating phases in squark decay

We present a new observable sensitive to a certain combination of CP violating phases in supersymmetric extensions of the Standard Model, viz. a triple product of momenta in the cascade decay of a heavy squark via an on-shell neutralino and off-shell slepton. We investigate the regions of parameter space in which the signal is strong enough to be detectable at the LHC with $\sim \bigl(10^2-10^3\bigr)/\sin^2(2\Delta\phi)$ identified events, where $\Delta\phi$ is a certain combination of phases in the MSSM presented in the text.Comment: Several references adde