9,144 research outputs found
Dirac points with giant spin-orbit splitting in the electronic structure of two-dimensional transition-metal carbides
Two-dimensional (2D) materials, especially their most prominent member,
graphene, have greatly influenced many scientific areas. Moreover, they have
become a base for investigating the relativistic properties of condensed matter
within the emerging field of Dirac physics. This has ignited an intense search
for new materials where charge carriers behave as massless or massive Dirac
fermions. Here, we theoretically show the existence of Dirac electrons in a
series of 2D transition-metal carbides, known as MXenes. They possess twelve
conical crossings in the 1st Brillouin zone with giant spin-orbit splitting.
Our findings indicate that the 2D band structure of MXenes is protected against
external perturbations and preserved even in multilayer phases. These results,
together with the broad possibilities to engineer the properties of these
materials phases, make Dirac MXenes a potential candidate for studying and
developing novel Dirac-physics-based technologies.Comment: 4 figures and supplementar
Coherent QCD phenomena in the Coherent Pion-Nucleon and Pion-Nucleus Production of Two Jets at High Relative Momenta
We use QCD to compute the cross section for coherent production of a di-jet
(treated as a moving at high relative transverse momentum,). In the target rest frame,the space-time evolution of this reaction is
dominated by the process in which the high component of
the pion wave function is formed before reaching the target. It then interacts
through two gluon exchange. In the approximation of keeping the leading order
in powers of and all orders in
the amplitudes for other processes are
shown to be smaller at least by a power of . The resulting dominant
amplitude is proportional to ( is the fraction
light-cone(+)momentum carried by the quark in the final state) times the skewed
gluon distribution of the target. For the pion scattering by a nuclear target,
this means that at fixed (but ) the nuclear process in which there is only a single interaction is the
most important one to contribute to the reaction. Thus in this limit color
transparency phenomena should occur.These findings are in accord with E971
experiment at FNAL. We also re-examine a potentially important nuclear multiple
scattering correction which is positive and . The
meaning of the signal obtained from the experimental measurement of pion
diffraction into two jets is also critically examined and significant
corrections are identified.We show also that for values of achieved
at fixed target energies, di-jet production by the e.m. field of the nucleus
leads to an insignificant correction which gets more important as
increases.Comment: 23 pages, 9 figure
Quantum collisions of finite-size ultrarelativistic nuclei
We show that the boost variable, the conjugate to the coordinate rapidity,
which is associated with the center-of-mass motion, encodes the information
about the finite size of colliding nuclei in a Lorentz-invariant way. The
quasi-elastic forward color-changing scattering between the quantum boost
states rapidly grows with the total energy of the collision and leads to an
active breakdown of the color coherence at the earliest moments of the
collision. The possible physical implications of this result are discussed.Comment: 23 pages, RevTeX. New references and two figures added. Final version
accepted for publication in Physical Review
Gravitational dynamics for all tensorial spacetimes carrying predictive, interpretable and quantizable matter
Only a severely restricted class of tensor fields can provide classical
spacetime geometries, namely those that can carry matter field equations that
are predictive, interpretable and quantizable. These three conditions on matter
translate into three corresponding algebraic conditions on the underlying
tensorial geometry, namely to be hyperbolic, time-orientable and
energy-distinguishing. Lorentzian metrics, on which general relativity and the
standard model of particle physics are built, present just the simplest
tensorial spacetime geometry satisfying these conditions. The problem of
finding gravitational dynamics---for the general tensorial spacetime geometries
satisfying the above minimum requirements---is reformulated in this paper as a
system of linear partial differential equations, in the sense that their
solutions yield the actions governing the corresponding spacetime geometry.
Thus the search for modified gravitational dynamics is reduced to a clear
mathematical task.Comment: 47 pages, no figures, minor update
On integrable boundaries in the 2 dimensional -models
We make an attempt to map the integrable boundary conditions for 2
dimensional non-linear O(N) -models. We do it at various levels:
classically, by demanding the existence of infinitely many conserved local
charges and also by constructing the double row transfer matrix from the Lax
connection, which leads to the spectral curve formulation of the problem; at
the quantum level, we describe the solutions of the boundary Yang-Baxter
equation and derive the Bethe-Yang equations. We then show how to connect the
thermodynamic limit of the boundary Bethe-Yang equations to the spectral curve.Comment: Dedicated to the memory of Petr Kulish, 31 pages, 1 figure, v2:
conformality and integrability of the boundary conditions are distinguishe
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