1,593 research outputs found
Mellin-Barnes Representation for the Genus-g Finite Temperature String Theory
The Mellin-Barnes representation for the free energy of the genus- string
is constructed. It is shown that the interactions of the open bosonic string do
not modify the critical (Hagedorn) temperature. However,for the sectors having
a spinor structure, the critical temperature exists also for all and
depends on the windings. The appearance of a periodic structure is briefly
discussed.Comment: 9 pages, report UTF 294 (1993
Transverse Enhancement Model and MiniBooNE Charge Current Quasi-Elastic Neutrino Scattering Data
Recently proposed Transverse Enhancement Model of nuclear effects in Charge
Current Quasi-Elastic neutrino scattering [A. Bodek, H. S. Budd, and M. E.
Christy, Eur. Phys. J. C{\bf 71} (2011) 1726] is confronted with the MiniBooNE
high statistics experimental data. It is shown that the {\it effective} large
axial mass model leads to better agreement with the data.Comment: 4 pages, 6 figure
Renormalizable 1/N_f Expansion for Field Theories in Extra Dimensions
We demonstrate how one can construct renormalizable perturbative expansion in
formally nonrenormalizable higher dimensional field theories. It is based on
-expansion and results in a logarithmically divergent perturbation
theory in arbitrary high space-time dimension. First, we consider a simple
example of -component scalar filed theory and then extend this approach to
Abelian and non-Abelian gauge theories with fermions. In the latter case,
due to self-interaction of non-Abelian fields the proposed recipe requires some
modification which, however, does not change the main results. The resulting
effective coupling is dimensionless and is running in accordance with the usual
RG equations. The corresponding beta function is calculated in the leading
order and is nonpolynomial in effective coupling. It exhibits either UV
asymptotically free or IR free behaviour depending on the dimension of
space-time. The original dimensionful coupling plays a role of a mass and is
also logarithmically renormalized. We analyze also the analytical properties of
a resulting theory and demonstrate that in general it acquires several ghost
states with negative and/or complex masses. In the former case, the ghost state
can be removed by a proper choice of the coupling. As for the states with
complex conjugated masses, their contribution to physical amplitudes cancels so
that the theory appears to be unitary.Comment: 32 pages, 20 figure
Supersymmetric Models with Higher Dimensional Operators
In 4D renormalisable theories, integrating out massive states generates in
the low energy effective action higher dimensional operators (derivative or
otherwise). Using a superfield language it is shown that a 4D N=1
supersymmetric theory with higher derivative operators in either the Kahler or
the superpotential part of the Lagrangian and with an otherwise arbitrary
superpotential, is equivalent to a 4D N=1 theory of second order (i.e. without
higher derivatives) with additional superfields and renormalised interactions.
We provide examples where a free theory with trivial supersymmetry breaking
provided by a linear superpotential becomes, in the presence of higher
derivatives terms and in the second order version, a non-trivial interactive
one with spontaneous supersymmetry breaking. The couplings of the equivalent
theory acquire a threshold correction through their dependence on the scale of
the higher dimensional operator(s). The scalar potential in the second order
theory is not necessarily positive definite, and one can in principle have a
vanishing potential with broken supersymmetry. We provide an application to
MSSM and argue that at tree-level and for a mass scale associated to a higher
derivative term in the TeV range, the Higgs mass can be lifted above the
current experimental limits.Comment: 36 pages; some clarifications and references adde
A Novel Representation for the Free Energy in String Theory at Non-Zero Temperature
A novel representation ---in terms of a Laurent series--- for the free energy
of string theory at non-zero temperature is constructed. The examples of open
bosonic, open supersymmetric and closed bosonic strings are studied in detail.
In all these cases the Laurent series representation for the free energy is
obtained explicitly.
It is shown that the Hagedorn temperature arises in this formalism as the
convergence condition (specifically, the radius of convergence) of the
corresponding Laurent series. Some prospects for further applications are also
discussed. In particular, an attempt to describe string theory above the
Hagedorn temperature ---via Borel analytical continuation of the Laurent series
representation--- is provided.Comment: 21 pages, LaTeX file, HUPD-92-12, UB-ECM-PF 92/25, UFT 273-9
Tensor decomposition processes for interpolation of diffusion magnetic resonance imaging
Diffusion magnetic resonance imaging (dMRI) is an established medical technique used for describing water diffusion in an organic tissue. Typically, rank-2 or 2nd-order tensors quantify this diffusion. From this quantification, it is possible to calculate relevant scalar measures (i.e. fractional anisotropy) employed in the clinical diagnosis of neurological diseases. Nonetheless, 2nd-order tensors fail to represent complex tissue structures like crossing fibers. To overcome this limitation, several researchers proposed a diffusion representation with higher order tensors (HOT), specifically 4th and 6th orders. However, the current acquisition protocols of dMRI data allow images with a spatial resolution between 1 mm3 and 2 mm3, and this voxel size is much bigger than tissue structures. Therefore, several clinical procedures derived from dMRI may be inaccurate. Concerning this, interpolation has been used to enhance the resolution of dMRI in a tensorial space. Most interpolation methods are valid only for rank-2 tensors and a generalization for HOT data is missing. In this work, we propose a probabilistic framework for performing HOT data interpolation. In particular, we introduce two novel probabilistic models based on the Tucker and the canonical decompositions. We call our approaches: Tucker decomposition process (TDP) and canonical decomposition process (CDP). We test the TDP and CDP in rank-2, 4 and 6 HOT fields. For rank-2 tensors, we compare against direct interpolation, log-Euclidean approach, and Generalized Wishart processes. For rank-4 and 6 tensors, we compare against direct interpolation and raw dMRI interpolation. Results obtained show that TDP and CDP interpolate accurately the HOT fields in terms of Frobenius distance, anisotropy measurements, and fiber tracts. Besides, CDP and TDP can be generalized to any rank. Also, the proposed framework keeps the mandatory constraint of positive definite tensors, and preserves morphological properties such as fractional anisotropy (FA), generalized anisotropy (GA) and tractography
Differential geometry construction of anomalies and topological invariants in various dimensions
In the model of extended non-Abelian tensor gauge fields we have found new
metric-independent densities: the exact (2n+3)-forms and their secondary
characteristics, the (2n+2)-forms as well as the exact 6n-forms and the
corresponding secondary (6n-1)-forms. These forms are the analogs of the
Pontryagin densities: the exact 2n-forms and Chern-Simons secondary
characteristics, the (2n-1)-forms. The (2n+3)- and 6n-forms are gauge invariant
densities, while the (2n+2)- and (6n-1)-forms transform non-trivially under
gauge transformations, that we compare with the corresponding transformations
of the Chern-Simons secondary characteristics. This construction allows to
identify new potential gauge anomalies in various dimensions.Comment: 27 pages, references added, matches published versio
Quantum Mass and Central Charge of Supersymmetric Monopoles - Anomalies, current renormalization, and surface terms
We calculate the one-loop quantum corrections to the mass and central charge
of N=2 and N=4 supersymmetric monopoles in 3+1 dimensions. The corrections to
the N=2 central charge are finite and due to an anomaly in the conformal
central charge current, but they cancel for the N=4 monopole. For the quantum
corrections to the mass we start with the integral over the expectation value
of the Hamiltonian density, which we show to consist of a bulk contribution
which is given by the familiar sum over zero-point energies, as well as surface
terms which contribute nontrivially in the monopole sector. The bulk
contribution is evaluated through index theorems and found to be nonvanishing
only in the N=2 case. The contributions from the surface terms in the
Hamiltonian are cancelled by infinite composite operator counterterms in the
N=4 case, forming a multiplet of improvement terms. These counterterms are also
needed for the renormalization of the central charge. However, in the N=2 case
they cancel, and both the improved and the unimproved current multiplet are
finite.Comment: 1+40 pages, JHEP style. v2: small corrections and additions,
references adde
Deformed Poincare Algebra and Field Theory
We examine deformed Poincar\'e algebras containing the exact Lorentz algebra.
We impose constraints which are necessary for defining field theories on these
algebras and we present simple field theoretical examples. Of particular
interest is a case that exhibits improved renormalization properties.Comment: 14 pages, LATEX, prep. MPI-Ph/94-5
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