969 research outputs found
An Effective Field Theory Look at Deep Inelastic Scattering
This talk discusses the effective field theory view of deep inelastic
scattering. In such an approach, the standard factorization formula of a hard
coefficient multiplied by a parton distribution function arises from matching
of QCD onto an effective field theory. The DGLAP equations can then be viewed
as the standard renormalization group equations that determines the cut-off
dependence of the non-local operator whose forward matrix element is the parton
distribution function. As an example, the non-singlet quark splitting functions
is derived directly from the renormalization properties of the non-local
operator itself. This approach, although discussed in the literature, does not
appear to be well known to the larger high energy community. In this talk we
give a pedagogical introduction to this subject.Comment: 11 pages, 1 figure, To appear in Modern Physics Letters
Nonperturbative calculation of the anomalous magnetic moment in the Yukawa model within truncated Fock space
Within the covariant formulation of light-front dynamics, we calculate the
state vector of a physical fermion in the Yukawa model. The state vector is
decomposed in Fock sectors and we consider the first three ones: the single
constituent fermion, the constituent fermion coupled to one scalar boson, and
the constituent fermion coupled to two scalar bosons. This last three-body
sector generates nontrivial and nonperturbative contributions to the state
vector, which are calculated numerically. Field-theoretical divergences are
regularized using Pauli-Villars fermion and boson fields. Physical observables
can be unambiguously deduced using a systematic renormalization scheme we have
developed previously. As a first application, we consider the anomalous
magnetic moment of the physical fermion.Comment: 24 pages, 16 figure
Systematic renormalization scheme in light-front dynamics with Fock space truncation
Within the framework of the covariant formulation of light-front dynamics, we
develop a general non-perturbative renormalization scheme based on the Fock
decomposition of the state vector and its truncation. The counterterms and bare
parameters needed to renormalize the theory depend on the Fock sectors. We
present a general strategy in order to calculate these quantities, as well as
state vectors of physical systems, in a truncated Fock space. The explicit
dependence of our formalism on the orientation of the light front plane is
essential in order to analyze the structure of the counterterms. We apply our
formalism to the two-body (one fermion and one boson) truncation in the Yukawa
model and in QED, and to the three-body truncation in a scalar model. In QED,
we recover analytically, without any perturbative expansion, the
renormalization of the electric charge, according to the requirements of the
Ward identity.Comment: 32 pages, 14 figures, submitted in Phys. Rev.
Induced current in the presence of magnetic flux tube of small radius
The induced current density, corresponding to the massless Dirac equation in
(2+1) dimensions in a magnetic flux tube of small radius is considered. This
problem is important for graphene. In the case, when an electron can not
penetrate the region of nonzero magnetic field, this current is the odd
periodical function of the magnetic flux. If the region inside the magnetic
tube is not forbidden for penetration of electron, the induced current is not a
periodical function of the magnetic flux. However in the limit , where
is the radius of magnetic flux tube, this function has the universal form
which is independent of the magnetic field distribution inside the magnetic
tube at fixed value of the magnetic flux.Comment: 5 pages, 1 figur
Cosmology With Many Light Scalar Fields: Stochastic Inflation and Loop Corrections
We explore the consequences of the existence of a very large number of light
scalar degrees of freedom in the early universe. We distinguish between
participator and spectator fields. The former have a small mass, and can
contribute to the inflationary dynamics; the latter are either strictly
massless or have a negligible VEV. In N-flation and generic assisted inflation
scenarios, inflation is a co-operative phenomenon driven by N participator
fields, none of which could drive inflation on their own. We review upper
bounds on N, as a function of the inflationary Hubble scale H. We then consider
stochastic and eternal inflation in models with N participator fields showing
that individual fields may evolve stochastically while the whole ensemble
behaves deterministically, and that a wide range of eternal inflationary
scenarios are possible in this regime. We then compute one-loop quantum
corrections to the inflationary power spectrum. These are largest with N
spectator fields and a single participator field, and the resulting bound on N
is always weaker than those obtained in other ways. We find that loop
corrections to the N-flation power spectrum do not scale with N, and thus place
no upper bound on the number of participator fields. This result also implies
that, at least to leading order, the theory behaves like a composite single
scalar field. In order to perform this calculation, we address a number of
issues associated with loop calculations in the Schwinger-Keldysh "in-in"
formalism.Comment: Typos corrected. Matches published versio
Mass of the higgs versus fourth generation masses
The predicted value of the higgs mass is analyzed assuming the
existence of the fourth generation of leptons () and quarks ().
The steep and flat directions are found in the five-dimensional parameter
space: , , , , . The LEPTOP fit of the precision
electroweak data is compatible (in particular) with GeV, GeV, GeV, GeV, and GeV. The quality of fits drastically improves when the data on b- and
c-quark asymmetries and new NuTeV data on deep inelastic scattering are
ignored.Comment: 8 pages, 4 figure
On the Significance of the Quantity "A Squared"
We consider the gauge potential A and argue that the minimum value of the
volume integral of A squared (in Euclidean space) may have physical meaning,
particularly in connection with the existence of topological structures. A
lattice simulation comparing compact and non-compact ``photodynamics'' shows a
jump in this quantity at the phase transition, supporting this idea.Comment: 6 pages, one figur
Non-commutative SU(N) gauge theories and asymptotic freedom
In this paper we analyze the one-loop renormalization of the
-expanded Yang-Mills theory. We show that the {\it freedom
parameter} , key to renormalization, originates from higher order
non-commutative gauge interaction, represented by a higher derivative term . The renormalization condition fixes the allowed values of the
parameter to one of the two solutions: or , i.e. to or to
, respectively. When the higher order interaction is switched on,
(), pure non-commutative SU(N) gauge theory at first order in
-expansion becomes one-loop renormalizable for various representations
of the gauge group. We also show that, in the case and the adjoint
representation of the gauge fields, the non-commutative deformation parameter
has to be renormalized and it is asymptotically free.Comment: 16 pages, no figure
Gravitational radiative corrections from effective field theory
In this paper we construct an effective field theory (EFT) that describes
long wavelength gravitational radiation from compact systems. To leading order,
this EFT consists of the multipole expansion, which we describe in terms of a
diffeomorphism invariant point particle Lagrangian. The EFT also systematically
captures "post-Minkowskian" corrections to the multipole expansion due to
non-linear terms in general relativity. Specifically, we compute long distance
corrections from the coupling of the (mass) monopole moment to the quadrupole
moment, including up to two mass insertions. Along the way, we encounter both
logarithmic short distance (UV) and long wavelength (IR) divergences. We show
that the UV divergences can be (1) absorbed into a renormalization of the
multipole moments and (2) resummed via the renormalization group. The IR
singularities are shown to cancel from properly defined physical observables.
As a concrete example of the formalism, we use this EFT to reproduce a number
of post-Newtonian corrections to the gravitational wave energy flux from
non-relativistic binaries, including long distance effects up to 3PN ()
order. Our results verify that the factorization of scales proposed in the NRGR
framework of Goldberger and Rothstein is consistent up to order 3PN.Comment: 37 pages, LaTeX. Published versio
Once more on extra quark-lepton generations and precision measurements
Precision measurements of -boson parameters and -boson and -quark
masses put strong constraints on non singlet New Physics. We
demonstrate that one extra generation passes electroweak constraints even when
all new particle masses are well above their direct mass bounds.Comment: Dedicated to L.B. Okun's 80th birthda
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