3,816 research outputs found
Effective Field Theory of pure Gravity and the Renormalization Group
The general structure of the renormalization group equations for the low
energy effective field theory formulation of pure gravity is presented. The
solution of these equations takes a particular simple form if the mass scale of
the effective theory is much smaller than the Planck mass (a possibility
compatible with the renormalization of the effective theory). A theory with
just one free renormalized parameter is obtained when contributions suppressed
by inverse powers of the Planck mass are neglected.Comment: latex, 9 pages, minor correction, version publishe
The Beginning of the End of the Anthropic Principle
We argue that if string theory as an approach to the fundamental laws of
physics is correct, then there is almost no room for anthropic arguments in
cosmology. The quark and lepton masses and interaction strengths are
determined.Comment: 12 page
Renormalization of the one-pion-exchange interaction
A renormalization scheme for the nucleon-nucleon (NN) interaction based on a
subtracted T-matrix equation is proposed and applied to the one-pion-exchange
potential supplemented by contact interactions. The singlet and triplet
scattering lengths are given to fix the renormalized strengths of the contact
interactions. With only one scaling parameter (), the results show an
overall very good agreement with neutron-proton data, particularly for the
observables related to the triplet channel. The agreement is qualitative in the
channel. Between the low-energy NN observables we have examined, the
mixing parameter of the states is the most sensible to the scale.
The scheme is renormalization group invariant for .Comment: 16 pages, 4 eps figures, to appear in Nuclear Physics
Do β-Defensins and Other Antimicrobial Peptides Play a Role in Neuroimmune Function and Neurodegeneration?
It is widely accepted that the brain responds to mechanical trauma and development of most neurodegenerative diseases with an inflammatory sequelae that was once thought exclusive to systemic immunity. Mostly cationic peptides, such as the β-defensins, originally assigned an antimicrobial function are now recognized as mediators of both innate and adaptive immunity. Herein supporting evidence is presented for the hypothesis that neuropathological changes associated with chronic disease conditions of the CNS involve abnormal expression and regulatory function of specific antimicrobial peptides. It is also proposed that these alterations exacerbate proinflammatory conditions within the brain that ultimately potentiate the neurodegenerative process
A Chiral Effective Lagrangian for Nuclei
An effective hadronic lagrangian consistent with the symmetries of quantum
chromodynamics and intended for applications to finite-density systems is
constructed. The degrees of freedom are (valence) nucleons, pions, and the
low-lying non-Goldstone bosons, which account for the intermediate-range
nucleon-nucleon interactions and conveniently describe the nonvanishing
expectation values of nucleon bilinears. Chiral symmetry is realized
nonlinearly, with a light scalar meson included as a chiral singlet to describe
the mid-range nucleon-nucleon attraction. The low-energy electromagnetic
structure of the nucleon is described within the theory using vector-meson
dominance, so that external form factors are not needed. The effective
lagrangian is expanded in powers of the fields and their derivatives, with the
terms organized using Georgi's ``naive dimensional analysis''. Results are
presented for finite nuclei and nuclear matter at one-baryon-loop order, using
the single-nucleon structure determined within the model. Parameters obtained
from fits to nuclear properties show that naive dimensional analysis is a
useful principle and that a truncation of the effective lagrangian at the first
few powers of the fields and their derivatives is justified.Comment: 43 pages, REVTeX 3.0 with epsf.sty, plus 12 figure
Many-body Fock sectors in Wick-Cutkosky model
In the model where two massive scalar particles interact by the ladder
exchanges of massless scalar particles (Wick-Cutkosky model), we study in
light-front dynamics the contributions of different Fock sectors (with
increasing number of exchanged particles) to full normalization integral and
electromagnetic form factor. It turns out that two-body sector always
dominates. At small coupling constant , its contribution is close
to 100%. It decreases with increase of . For maximal value
, corresponding to the zero bound state mass, two-body sector
contributes to the normalization integral 64%, whereas the three-body
contribution is 26% and the sum of all higher contributions from four- to
infinite-body sectors is 10%. Contributions to the form factor from different
Fock sectors fall off faster for asymptotically large , when the number of
particles in the Fock sectors becomes larger. So, asymptotic behavior of the
form factor is determined by the two-body Fock sector.Comment: 36 pages, 16 figure
The Proton Spin in the Chiral Bag Model : Casimir Contribution and Cheshire Cat Principle
The flavor singlet axial charge has been a source of study in the last years
due to its relation to the so called {\it Proton Spin Problem}. The relevant
flavor singlet axial current is anomalous, i.e., its divergence contains a
piece which is the celebrated anomaly. This anomaly is intimately
associated with the meson, which gets its mass from it. When the
gauge degrees of freedom of QCD are confined within a volume as is presently
understood, the anomaly is known to induce color anomaly leading to
"leakage" of the color out of the confined volume (or bag). For consistency of
the theory, this anomaly should be canceled by a boundary term. This ``color
boundary term" inherits part or most of the dynamics of the volume (i.e., QCD).
In this paper, we exploit this mapping of the volume to the surafce via the
color boundary condition to perform a complete analysis of the flavor singlet
axial charge in the chiral bag model using the Cheshire Cat Principle. This
enables us to obtain the hitherto missing piece in the axial charge associated
with the gluon Casimir energies. The result is that the flavor singlet axial
charge is small independent of the confinement (bag) size ranging from the
skyrmion picture to the MIT bag picture, thereby confirming the (albeit
approximate) Cheshire Cat phenomenon.Comment: 18 pages, 6 figure
Effect of Zero Modes on the Bound-State Spectrum in Light-Cone Quantisation
We study the role of bosonic zero modes in light-cone quantisation on the
invariant mass spectrum for the simplified setting of two-dimensional SU(2)
Yang-Mills theory coupled to massive scalar adjoint matter. Specifically, we
use discretised light-cone quantisation where the momentum modes become
discrete. Two types of zero momentum mode appear -- constrained and dynamical
zero modes. In fact only the latter type of modes turn out to mix with the Fock
vacuum. Omission of the constrained modes leads to the dynamical zero modes
being controlled by an infinite square-well potential. We find that taking into
account the wavefunctions for these modes in the computation of the full bound
state spectrum of the two dimensional theory leads to 21% shifts in the masses
of the lowest lying states.Comment: LaTeX with 5 postscript file
Systematic Renormalization in Hamiltonian Light-Front Field Theory
We develop a systematic method for computing a renormalized light-front field
theory Hamiltonian that can lead to bound states that rapidly converge in an
expansion in free-particle Fock-space sectors. To accomplish this without
dropping any Fock sectors from the theory, and to regulate the Hamiltonian, we
suppress the matrix elements of the Hamiltonian between free-particle
Fock-space states that differ in free mass by more than a cutoff. The cutoff
violates a number of physical principles of the theory, and thus the
Hamiltonian is not just the canonical Hamiltonian with masses and couplings
redefined by renormalization. Instead, the Hamiltonian must be allowed to
contain all operators that are consistent with the unviolated physical
principles of the theory. We show that if we require the Hamiltonian to produce
cutoff-independent physical quantities and we require it to respect the
unviolated physical principles of the theory, then its matrix elements are
uniquely determined in terms of the fundamental parameters of the theory. This
method is designed to be applied to QCD, but for simplicity, we illustrate our
method by computing and analyzing second- and third-order matrix elements of
the Hamiltonian in massless phi-cubed theory in six dimensions.Comment: 47 pages, 6 figures; improved referencing, minor presentation change
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