Space-time compactification induced by nonlinear sigma models,gauge fields and submersions

The nonlinear sigma model coupled to gravity in (4+K) dimensions is used to trigger the compactification of space-time. A very general class of solutions is given by submersions from the extradimensional space onto the space in which the scalar fields take values. The existence of some vertical Killing vectors on the extra space can produce massless gauge bosons.Presented at the International Conference Selected Topics in Quantum Field Theory and Mathematical Physics, Bechyn, Czechoslovakia, June 23–27, 1986.     

Observing the geometry of warped compactification via cosmic inflation

Using Dirac-Born-Infeld inflation as an example, we demonstrate that the detailed geometry of warped compactification can leave an imprint on the cosmic microwave background. We compute cosmic microwave background observables for Dirac-Born-Infeld inflation in a generic class of warped throats and find that the results (such as the sign of the tilt of the scalar perturbations and its running) depend sensitively on the precise shape of the warp factor. In particular, we analyze the warped deformed conifold and find that the results can differ from those of other warped geometries, even when these geometries approximate well the exact metric of the warped deformed conifold.     

Space-time phase transitions in driven kinetically constrained lattice models

Kinetically constrained models (KCMs) have been widely used to study and understand the origin of glassy dynamics. These models show an ergodic-nonergodic first-order phase transition between phases of distinct dynamical “activity”. We introduce driven variants of two popular KCMs, the FA model and the (2)-TLG, as models for driven supercooled liquids. By classifying trajectories through their entropy production we prove that driven KCMs display an analogous first-order space-time transition between dynamical phases of finite and vanishing entropy production. We discuss how trajectories with rare values of entropy production can be realized as typical trajectories of a mapped system with modified forces.     

Space-time description of colour screening via jet calculus techniques

The branching process characterizing the perturbative development of a chromodynamic jet up to the formation of colour singlet clusters is studied in real space-time with jet calculus techniques. Whereas the space-time separation of generic partons increases indefinitely with energy (or momentum transfer), such a separation remains finite within each colour singlet system in its own rest frame. These results add further appeal and overall consistency to the preconfinement picture.     

Localization of five-dimensional Elko spinors on dS/AdS thick branes

Owing to the special structure of a five-dimensional Elko spinor, its localization on a brane with codimension one becomes completely different from that of a Dirac spinor. By introducing the coupling between the Elko spinor and the scalar field that can generate the brane, we have two types of localization mechanism for the five-dimensional Elko spinor zero mode on a brane. One is the Yukawa-type coupling, and the other is the non-minimal coupling. In this study, we investigate the localization of the Elko zero mode on de Sitter and Anti-de Sitter thick branes with the two localization mechanisms, respectively. The results show that both the mechanisms can achieve localization. The forms of the scalar coupling function in both localization mechanisms have similar properties, and they play a similar role in localization.     

Nuclear excitation via free-bound muon atomic transitions

We have examined the probability of the excitation of the giant nuclear dipole resonance through the radiationless capture of a free muon into a bound orbit. Our calculation predicts that the probability is extremely small, about 4 × 10^?5 per stopping muon in lead in the surface transition model.     

Green functions and twist correlators for N branes at angles

We compute the Green functions and correlator functions for N   twist fields for branes at angles on T²$T^2$ and we show that there are N−2$N-2$ different configurations labeled by an integer M   which is roughly associated with the number of reflex angles of the configuration. In order to perform this computation we use an SL(2,R)$\mathit{SL}(2,\mathbb{R})$ invariant formulation and geometric constraints instead of Pochammer contours. In particular the M=1$M=1$ or M=N−1$M=N-1$ amplitude can be expressed without using transcendental functions. We determine the amplitudes normalization from N→N−1$N\to N-1$ reduction without using the factorization into the untwisted sector. Both the amplitudes normalization and the OPE of two twist fields are unique (up to one constant) when the ?↔1−?$?\leftrightarrow 1-?$ symmetry is imposed. For consistency we find also an infinite number of relations among Lauricella hypergeometric functions.     

Space-time resolved reflectivity measurements of picosecond laser-pulse induced phase transitions in (111) silicon surface layers

The changes in reflectivity of a silicon surface, irradiated by a green picosecond pulse, are probed during and following that pulse with a spatial resolution of 10 m. The data indicate the development of a liquid phase, and a resolidification either into a single crystal or an amorphous phase. The latter has a characteristic ring-type pattern, and occurs only at locations where the incident picosecond laser fluence lies between 0.2 and 0.26 J/cm². The reflectivity data appear to be in good quantitative agreement with a simple heating model, in which the electrons and phonons maintain a local thermodynamic equilibrium on a picosecond time scale.On leave from Philips Research Laboratories, D-2000 Hamburg 54, F. R. Germany     

Characteristics of phase transitions via intervention in random networks

We present a percolation process in which the classical Erdo¨s–Re′nyi(ER) random evolutionary network is intervened by the product rule(PR) from some moment t0. The parameter t0is continuously tunable over the real interval [0, 1].This model becomes the random network under the Achlioptas process at t0= 0 and the ER network at t0= 1. For the percolation process at t0≤ 1, we introduce a relatively slow-growing point, after which the largest cluster begins growing faster than that in the ER model. A weakly discontinuous transition is generated in the percolation process at t0≤ 0.5.We take the relatively slow-growing point as the lower pseudotransition point and the maximum gap point of the order parameter as the upper pseudotransition point. The critical point can be approximately predicted by each fitting function of the two points about t0. This contributes to understanding the rapid mergence of the large clusters at the critical point.The numerical simulations indicate that the lower pseudotransition point and the upper pseudotransition point are equal in the thermodynamic limit. When t0> 0.5, the percolation processes generate a continuous transition. The scaling analyses of several quantities are presented, including the relatively slow-growing point, the duration of the relatively slow-growing process, as well as the relatively maximum strength between the percolation percolation at t0< 1 and the ER network about different t0. The presented mechanism can be viewed as a two-stage percolation process that has many potential applications in the growth processes of real networks.     

Self-broadening of water vapor transitions via the complex Robert-Bonamy theory

Calculations of self-broadened half-widths and self-induced pressure shifts are made using the complex Robert-Bonamy formalism. The results of calculations using different approximations of the intermolecular potential indicate that this is a strong collision system. The effects of the imaginary components on the half-widths are studied. The temperature, vibrational, and rotational state dependence of the half-width are investigated. Results are compared with measurements from the database of self-broadening of water vapor [Gamache RR, Hartmann J-M. An intercomparison of measured pressure-broadening and pressure-shifting parameters of water vapor. Can J Chem 2004; 82: 1013-27].     

N = 2, D = 10 non-chiral supergravity and its spontaneous compactification

The non-chiral N = 2, D = 10 supergravity theory is constructed using dimensional reduction from N = 1, D = 11 supergravity. It is shown that this theory may spontaneously compactify, yielding S⁴ × S², CP² × S² and S² × S² × S² spaces for the extra dimensions.     

Inter and intrasubband transitions via LO phonons in quantum wires

We investigate the effects of the finite confining potential V₀ on the absorption and emission scattering rates of electrons interacting with LO phonons for a cylindrical GaAs quantum wire. The emission rates are qualitatively similar to those of the 2D case. The absorption rates on the other hand exhibit two different regimes: 1) for a wire radius smaller than a certain value (80 Å in the case where V₀ = 190 meV) the behavior is similar to the 2D and 3D analogues, but 2) for larger radius the absorption rates initially increase with increasing energy, reach a maximum value and then decrease monotonicaly. A complete study is made as a function of wire radius, and electron energy.     

Structural transitions in NaNH_2 via recrystallization under high pressure

Multiple phase transitions are detected in sodium amide(NaNH_2), an important hydrogen storage material, upon compression in diamond anvil cells(DAC) by using Raman spectroscopy and x-ray diffraction(XRD) measurements.Additional Bragg reflections appear on lower and higher angle sides of the original ones at ～1.07 GPa and 1.84 GPa,accompanied by obvious changes in Raman spectroscopy, respectively.It reveals that NaNH_2 undergoes the high-pressure phase sequence(α–β–γ) up to 20 GPa at room temperature.Spectral analysis indicates an orthorhombic structure with PBAN space group for the γ phase.We also experimentally observe high pressure induced recrystallization in alkaline amide compounds for the first time.     

Hyperfine transitions and fusion in flight via the Faddeev approach

The Faddeev approach, modified for long-range Coulomb forces, is used to study the s-wave scattering states of the muonic atomic systems p+pµ, d+dµ, t+tµ, t+dµ and d+tµ. Elastic and hyperfine-transition cross sections of p+pµ are calculated with and without the hyperfme splitting. Fusion-in-flight reactions are studied. A sharp resonance of the rate of fusion-in-flight is observed for d+tµ atE=76.3 eV. A similar resonance-like behavior of the fusion-in-flight is also obtained in the symmetric mesic atomic collisions.     

Lifshitz transitions via the type-II dirac and type-II Weyl points

The type-II Weyl and type-II Dirac points emerge in semimetals and in relativistic systems. In particular, the type-II Weyl fermions may emerge behind the event horizon of black holes. The type-II Weyl and Dirac points also emerge as the intermediate states of the topological Lifshitz transitions. In one case, the type-II Weyl point connects the Fermi pockets, and the Lifshitz transition corresponds to the transfer of the Berry flux between the Fermi pockets. In the other case, the type-II Weyl point connects the outer and inner Fermi surfaces. At the Lifshitz transition, the Weyl point is released from both Fermi surfaces. They loose their Berry flux, which guarantees the global stability, and without the topological support, the inner surface disappears after shrinking to a point at the second Lifshitz transition. These examples reveal the complexity and universality of topological Lifshitz transitions, which originate from the ubiquitous interplay of a variety of topological characters of the momentum-space manifolds.