144,432 research outputs found
Spin-Spin Interactions in Gauge Theory of Gravity, Violation of Weak Equivalence Principle and New Classical Test of General Relativity
For a long time, it is generally believed that spin-spin interactions can
only exist in a theory where Lorentz symmetry is gauged, and a theory with
spin-spin interactions is not perturbatively renormalizable. But this is not
true. By studying the motion of a spinning particle in gravitational field, it
is found that there exist spin-spin interactions in gauge theory of gravity.
Its mechanism is that a spinning particle will generate gravitomagnetic field
in space-time, and this gravitomagnetic field will interact with the spin of
another particle, which will cause spin-spin interactions. So, spin-spin
interactions are transmitted by gravitational field. The form of spin-spin
interactions in post Newtonian approximations is deduced. This result can also
be deduced from the Papapetrou equation. This kind of interactions will not
affect the renormalizability of the theory. The spin-spin interactions will
violate the weak equivalence principle, and the violation effects are
detectable. An experiment is proposed to detect the effects of the violation of
the weak equivalence principle.Comment: 17 pages, no figur
Recent advances in 3D printing of biomaterials.
3D Printing promises to produce complex biomedical devices according to computer design using patient-specific anatomical data. Since its initial use as pre-surgical visualization models and tooling molds, 3D Printing has slowly evolved to create one-of-a-kind devices, implants, scaffolds for tissue engineering, diagnostic platforms, and drug delivery systems. Fueled by the recent explosion in public interest and access to affordable printers, there is renewed interest to combine stem cells with custom 3D scaffolds for personalized regenerative medicine. Before 3D Printing can be used routinely for the regeneration of complex tissues (e.g. bone, cartilage, muscles, vessels, nerves in the craniomaxillofacial complex), and complex organs with intricate 3D microarchitecture (e.g. liver, lymphoid organs), several technological limitations must be addressed. In this review, the major materials and technology advances within the last five years for each of the common 3D Printing technologies (Three Dimensional Printing, Fused Deposition Modeling, Selective Laser Sintering, Stereolithography, and 3D Plotting/Direct-Write/Bioprinting) are described. Examples are highlighted to illustrate progress of each technology in tissue engineering, and key limitations are identified to motivate future research and advance this fascinating field of advanced manufacturing
Topological insulators are tunable waveguides for hyperbolic polaritons
Layered topological insulators, for example, BiSe are optically
hyperbolic materials in a range of THz frequencies. Such materials possess
deeply subdiffractional, highly directional collective modes: hyperbolic
phonon-polaritons. In thin crystals the dispersion of such modes is split into
discrete subbands and is strongly influenced by electron surface states. If the
surface states are doped, then hybrid collective modes result from coupling of
the phonon-polaritons with surface plasmons. The strength of the hybridization
can be controlled by an external gate that varies the chemical potential of the
surface states. Momentum-dependence of the plasmon-phonon coupling leads to a
polaritonic analog of the Goos-H\"anchen effect. Directionality of the
polaritonic rays and their tunable Goos-H\"anchen shift are observable via THz
nanoimaging.Comment: 12 pages, 7 figure
Coulomb drag in double quantum wells with a perpendicular magnetic field
Momentum transfer due to electron-electron interaction (Coulomb drag) between
two quantum wells, separated by a distance , in the presence of a
perpendicular magnetic field, is studied at low temperatures. We find besides
the well known Shubnikov-de Haas oscillations, which also appear in the drag
effect, the momentum transfer is markedly enhanced by the magnetic field.Comment: 8 pages, Revtex, 4 Postscript figures are available upon request,
Accepted by Mod. Phys. Lett.
Phenomenology from a U(1) gauged hidden sector
We consider the phenomenological consequences of a hidden Higgs sector
extending the Standard Model (SM), in which the matter content are uncharged
under the SM gauge groups. We consider a simple case where the hidden sector is
gauged under a U(1) with one Higgs singlet. The only couplings between SM and
the hidden sector are through mixings between the neutral gauge bosons of the
two respective sectors, and between the Higgs bosons. We find signals testable
at the LHC that can reveal the existence and shed light on the nature of such a
hidden sector.Comment: 5 pages, 2 figures. Talk given at the Lake Louise Winter Institute
2007, Feb. 19-24, Alberta, Canad
Testing Realistic Quark Mass Matrices in the Custodial Randall-Sundrum Model with Flavor Changing Top Decays
We study quark mass matrices in the Randall-Sundrum (RS) model with bulk
symmetry . The Yukawa couplings are
assumed to be within an order of magnitude of each other, and perturbative. We
find that quark mass matrices of the symmetrical form proposed by Koide
\textit{et. al.} [Y. Koide, H. Nishiura, K. Matsuda, T. Kikuchi and T.
Fukuyama, Phys. Rev. D {\bf 66}, 093006 (2002)] can be accommodated in the RS
framework with the assumption of hierarchyless Yukawa couplings, but not the
hermitian Fritzsch-type mass matrices. General asymmetrical mass matrices are
also found which fit well simultaneously with the quark masses and the
Cabibbo-Kobayashi-Maskawa matrix. Both left-handed (LH) and right-handed (RH)
quark rotation matrices are obtained that allow analysis of flavour changing
decay of both LH and RH top quarks. At a warped down scale of 1.65 TeV, the
total branching ratio of t \ra Z + jets can be as high as for symmetrical mass matrices and for
asymmetrical ones. This level of signal is within reach of the LHC.Comment: 30 pages, 6 figures. Reference added, typos corrected, discussions in
Sec. IV B expanded. Version conforms to the published versio
A Very Narrow Shadow Extra Z-boson at Colliders
We consider the phenomenological consequences of a hidden Higgs sector
extending the Standard Model (SM), in which the ``shadow Higgs'' are uncharged
under the SM gauge groups. We consider a simple U(1) model with one Higgs
singlet. One mechanism which sheds light on the shadow sector is the mixing
between the neutral gauge boson of the SM and the additional U(1) gauge group.
The mixing happens through the usual mass-mixing and also kinetic-mixing, and
is the only way the ``shadow '' couples to the SM. We study in detail
modifications to the electroweak precision tests (EWPTs) that the presence of
such a shadow sector would bring, which in turn provide constraints on the
kinetic-mixing parameter, , left free in our model. The shadow
production rate at the LHC and ILC depends on . We find that
observable event rate at both facilities is possible for a reasonable range of
allowed by EWPTs.Comment: 10 pages, 7 figures. Note and refs. adde
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