1,651 research outputs found
Renormalization Group Improved Radiative Corrections to the Supersymmetric Higgs Boson Masses
The one-loop radiative corrections to the Higgs boson potential in the MSSM,
originating from the top quark and squark loops, are summed in the leading log
approximation using the renormalization group. The RG improved effective
potential is minimized and the corrections to the CP-odd and CP-even Higgs
boson masses are calculated. The resulting masses exhibit smoother top mass
dependence than those calculated without RG summation. We have also found that
for preferable values of the top mass the light Higgs mass does not exceed 100
GeV.Comment: 10 PAGES, 1 FIGURE ENCLOSED, LATE
IS (Low Energy) SUSY STILL ALIVE?
Supersymmetry, a new symmetry that relates bosons and fermions in particle
physics, still escapes observation. Search for supersymmetry is one of the main
aims of the Large Hadron Collider. The other possible manifestation of
supersymmetry is the Dark Matter in the Universe. The present lectures contain
a brief introduction to supersymmetry in particle physics. The main notions of
supersymmetry are introduced. The supersymmetric extension of the Standard
Model -- the Minimal Supersymmetric Standard Model -- is considered in more
detail. Phenomenological features of the Minimal Supersymmetric Standard Model
as well as possible experimental signatures of supersymmetry at the Large
Hadron Collider are described. The present limits on supersymmetric particles
are presented and the allowed region of parameter space of the MSSM is shown.Comment: 59 pages, 35 figures, PDFLatex, Lectures at the European School of
High-Energy Physics, June 2012, Anjou, Franc
Conformal Invariance = Finiteness and Beta Deformed N=4 SYM Theory
We claim that if by a choice of the couplings the theory can be made
conformally invariant (vanishing of the beta functions) it is automatically
finite and vice versa. This is demonstrated by explicit example in
supersymmetric gauge theory. The formalism is then applied to the beta deformed
SYM theory and it is shown that the requirement of conformal
invariance = finiteness can be achieved for any complex parameter of
deformations.Comment: 15 pages, Latex, 1 figure axodraw styl
Difficulties of an Infrared Extension of Differential Renormalization
We investigate the possibility of generalizing differential renormalization
of D.Z.Freedman, K.Johnson and J.I.Latorre in an invariant fashion to theories
with infrared divergencies via an infrared operation.
Two-dimensional models and the four-dimensional theory
diagrams with exceptional momenta are used as examples, while dimensional
renormalization serves as a test scheme for comparison. We write the basic
differential identities of the method simultaneously in co-ordinate and
momentum space, introducing two scales which remove ultraviolet and infrared
singularities. The consistent set of Fourier-transformation formulae is
derived. However, the values for tadpole-type Feynman integrals in higher
orders of perturbation theory prove to be ambiguous, depending on the order of
evaluation of the subgraphs. In two dimensions, even earlier than this
ambiguity manifests itself, renormalization-group calculations based on
infrared extension of differential renormalization lead to incorrect results.
We conclude that the extended differential renormalization procedure does not
perform the infrared operation in a self-consistent way, as the
original recipe does the ultraviolet operation.Comment: (minor changes have been made to make clear that no infrared problems
occur in the original ultraviolet procedure of [1]; subsection 2.1 has been
added to outline the ideas a simple example), 26 pages, LaTeX, JINR preprint
E2-92-538, Dubna (Dec.1992
Challenges of D=6 N=(1,1) SYM Theory
Maximally supersymmetric Yang-Mills theories have several remarkable
properties, among which are the cancellation of UV divergences, factorization
of higher loop corrections and possible integrability. Much attention has been
attracted to the N=4 D=4 SYM theory. The N=(1,1) D=6 SYM theory possesses
similar properties but is nonrenomalizable and serves as a toy model for
supergravity. We consider the on-shell four point scattering amplitude and
analyze its perturbative expansion within the spin-helicity and superspace
formalism. The integrands of the resulting diagrams coincide with those of the
N=4 D=4 SYM and obey the dual conformal invariance. Contrary to 4 dimensions,
no IR divergences on mass shell appear. We calculate analytically the leading
logarithmic asymptotics in all loops. Their summation leads to a Regge
trajectory which is calculated exactly. The leading powers of s are calculated
up to six loops. Their summation is performed numerically and leads to a smooth
function of s. The leading UV divergences are calculated up to 5 loops. The
result suggests the geometrical progression which ends up in a finite
expression. This leads us to a radical point of view on nonrenormalizable
theories.Comment: 11 pages, 2 figures, Late
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