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Full-Text Articles in Physics
Tensorial Reconstruction At The Integrand Level, G. Heinrich, Giovanni Ossola, T. Reiter, F. Tramontano
Tensorial Reconstruction At The Integrand Level, G. Heinrich, Giovanni Ossola, T. Reiter, F. Tramontano
Publications and Research
We present a new approach to the reduction of one-loop amplitudes obtained by reconstructing the tensorial expression of the scattering amplitudes. The reconstruction is performed at the integrand level by means of a sampling in the integration momentum. There are several interesting applications of this novel method within existing techniques for the reduction of one-loop multi-leg amplitudes: to deal with numerically unstable points, such as in the vicinity of a vanishing Gram determinant; to allow for a sampling of the numerator function based on real values of the integration momentum; to optimize the numerical reduction in the case of long …
Scattering Amplitudes From Unitarity-Based Reduction Algorithm At The Integrand-Level, P. Mastrolia, Giovanni Ossola, T. Reiter, F. Tramontano
Scattering Amplitudes From Unitarity-Based Reduction Algorithm At The Integrand-Level, P. Mastrolia, Giovanni Ossola, T. Reiter, F. Tramontano
Publications and Research
Samurai is a tool for the automated numerical evaluation of one-loop corrections to any scattering amplitudes within the dimensional-regularization scheme. It is based on the decomposition of the integrand according to the OPP-approach, extended to accommodate an implementation of the generalized d-dimensional unitarity-cuts technique, and uses a polynomial interpolation exploiting the Discrete Fourier Transform. samurai can process integrands written either as numerator of Feynman diagrams or as product of tree-level amplitudes. We discuss some applications, among which the 6- and 8-photon scattering in QED, and the 6-quark scattering in QCD. samurai has been implemented as a Fortran90 library, publicly available, …
On The Feasibility Of A Timely Transition To A More Sustainable Energy Future, Micha Tomkiewicz
On The Feasibility Of A Timely Transition To A More Sustainable Energy Future, Micha Tomkiewicz
Publications and Research
The paper uses the framework of the IPAT equation, as applied to CO2 emission, to decompose the various driving forces in the global energy use. Data from recent history are superimposed on projections of SRES IPCC scenarios to determine if enough sustainable capacity can be built to prevent irreversible ecological deterioration. The conclusion from the analysis is that, in agreement with the IPCC 4th report, until about 2030 there are no large differences between a sustainable scenario and the one that resembles “business as usual”. The sharp divergence that follows stems from different estimates in population growth and in the …
Rotational Doppler Effect In Magnetic Resonance, S Ledinez, Eugene M. Chudnovsky, Javier Tejada
Rotational Doppler Effect In Magnetic Resonance, S Ledinez, Eugene M. Chudnovsky, Javier Tejada
Publications and Research
We compute the shift in the frequency of the spin resonance in a solid that rotates in the field of a circularly polarized electromagnetic wave. Electron spin resonance, nuclear magnetic resonance, and ferromagnetic resonance are considered. We show that contrary to the case of the rotating LC circuit, the shift in the frequency of the spin resonance has strong dependence on the symmetry of the receiver. The shift due to rotation occurs only when rotational symmetry is broken by the anisotropy of the gyromagnetic tensor, by the shape of the body, or by magnetocrystalline anisotropy. General expressions for the resonance …
Edges And Diffractive Effects In Casimir Energies, Daniel N. Kabat, Dimitra Karabali, V P. Nair
Edges And Diffractive Effects In Casimir Energies, Daniel N. Kabat, Dimitra Karabali, V P. Nair
Publications and Research
The prototypical Casimir effect arises when a scalar field is confined between parallel Dirichlet boundaries. We study corrections to this when the boundaries themselves have apertures and edges. We consider several geometries: a single plate with a slit in it, perpendicular plates separated by a gap, and two parallel plates, one of which has a long slit of large width, related to the case of one plate being semi-infinite. We develop a general formalism for studying such problems, based on the wavefunctional for the field in the gap between the plates. This formalism leads to a lower dimensional theory defined …
Single Magnetic Molecule Between Conducting Leads: Effect Of Mechanical Rotations, Reem Jaafar, Eugene M. Chudnovsky, Dmitry A. Garanin
Single Magnetic Molecule Between Conducting Leads: Effect Of Mechanical Rotations, Reem Jaafar, Eugene M. Chudnovsky, Dmitry A. Garanin
Publications and Research
We study spin-rotation effects in a magnetic molecule bridge d between two conducting leads. Dy- namics of the total angular momentum couples spin tunneling to the mechanical rotations. Landau- Zener spin transition produced by the time-dependent magne tic field generates a unique pattern of mechanical oscillations that can be detected by measuring t he electronic tunneling current through the molecule.
Interaction Of A Nanomagnet With A Weak Superconducting Link, Liufei Cai, Eugene M. Chudnovsky
Interaction Of A Nanomagnet With A Weak Superconducting Link, Liufei Cai, Eugene M. Chudnovsky
Publications and Research
We study electromagnetic interaction of a nanomagnet with a weak superconducting link. Equations that govern coupled dynamics of the two systems are derived and investigated numerically. We show that the presence of a small magnet in the proximity of a weak link may be detected through Shapiro-like steps caused by the precession of the magnetic moment. Despite very weak magnetic field generated by the weak link, a time-dependent bias voltage applied to the link can initiate a non-linear dynamics of the nanomagnet that leads to the reversal of its magnetic moment. We also consider quantum problem in which a nanomagnet …
Rotational States Of Magnetic Molecules, Eugene M. Chudnovsky, Dmitry A. Garanin
Rotational States Of Magnetic Molecules, Eugene M. Chudnovsky, Dmitry A. Garanin
Publications and Research
We study a magnetic molecule that exhibits spin tunneling and is free to rotate about its anisotropy axis. Exact low-energy eigenstates of the molecule that are superpositions of spin and rotational states are obtained. We show that parameter α=2(ℏS)2/(IΔ) determines the ground state of the molecule. Here ℏS is the spin, I is the moment of inertia, and Δ is the tunnel splitting. The magnetic moment of the molecule is zero at α<αc=[1−1/(2S)2]−1 and non-zero at α>αc. At α→∞ the spin of the molecule localizes in one of the directions along the anisotropy axis.
Deflagration With Quantum And Dipolar Effects In A Model Of A Molecular Magnet, Dmitry A. Garanin
Deflagration With Quantum And Dipolar Effects In A Model Of A Molecular Magnet, Dmitry A. Garanin
Publications and Research
Combination of the thermal effet in magnetic deflagration with resonance spin tunneling controlled by the dipole-dipole interaction in molecular magnets leads to the increase of the deflagration speed in the dipolar window near tunneling resonances.
On The Casimir Interaction Between Holes In A Plate, Daniel N. Kabat, Dimitra Karabali, V P. Nair
On The Casimir Interaction Between Holes In A Plate, Daniel N. Kabat, Dimitra Karabali, V P. Nair
Publications and Research
We study the leading long-distance attractive force between two holes in a plate arising from a scalar eld with Dirichlet boundary conditions on the plate. We use a formalism in which the interaction is governed by a non-local eld theory which lives on the two holes. The interaction energy is proportional to Q1Q2=r7 at large separation r, where Q1 and Q2 are certain charges associated with the holes. We compute these charges for round and rectangular holes. We show that the 1=r7 behavior is universal for separations large compared to the linear dimensions of the holes, irrespective of the spin …
The Hamiltonian Approach To Yang-Mills (2 + 1): Expansion Scheme And Corrections To String Tension, Dimitra Karabali, V P. Nair, Alexandr Yelinkov
The Hamiltonian Approach To Yang-Mills (2 + 1): Expansion Scheme And Corrections To String Tension, Dimitra Karabali, V P. Nair, Alexandr Yelinkov
Publications and Research
We carry out further analysis of the Hamiltonian approach to Yang-Mills theory in 2+1 dimensions which helps to place the calculation of the vacuum wave function and the string tension in the context of a systematic expansion scheme. The solution of the Schrodinger equation is carried out recursively. The computation of correlators is re-expressed in terms of a two-dimensional chiral boson theory. The effective action for this theory is calculated to first order in our expansion scheme and to the fourth order in a kinematic expansion parameter. The resulting corrections to the string tension are shown to be very small, …
Dipolar Ordering In Crystals Of Mn12 Ac, Dmitry A. Garanin
Dipolar Ordering In Crystals Of Mn12 Ac, Dmitry A. Garanin
Publications and Research
Ordering in realistic elongated box-shape crystals of the molecular magnet Mn_12 Ac is investigated with the site-resolved mean-field approximation that does not assume a uniform ordering. It is shown that ferromagnetic ordering should not occur in crystals with the aspect ratio up to 12. Instead, for the aspect ratio about 6, the inner and outer regions of the crystal order in different directions, uniformly along its length. Finding ordering temperature by extrapolating the inverse susceptibility curve does not provide a correct T_C.
Dynamical Decompactification And Three Large Dimensions, Brian Greene, Daniel N. Kabat, Stefanos Marnerides
Dynamical Decompactification And Three Large Dimensions, Brian Greene, Daniel N. Kabat, Stefanos Marnerides
Publications and Research
We study string gas dynamics in the early universe and seek to realize the Brandenberger - Vafa mechanism - a goal that has eluded earlier works - that singles out three or fewer spatial dimensions as the number which grow large cosmologically. Considering wound string interactions in an impact parameter picture, we show that a strong exponential suppression in the interaction rates for d > 3 spatial dimensions reflects the classical argument that string worldsheets generically intersect in at most four spacetime dimensions. This description is appropriate in the early universe if wound strings are heavy - wrapping long cycles - …