arXiv subjects

D. I. Kazakov

Publications and source records attributed to D. I. Kazakov.

At least 91 records · Page 5Linked to original sources

arXiv2002

Ultraviolet Fixed Points in Gauge and SUSY Field Theories in Extra Dimensions

We consider gauge field theories in $D>4$ following the Wilson RG approach and show that they possess the ultraviolet fixed points where the gauge coupling is dimensionless in any space-time dimension. At the fixed point the anomalous dimensions of the field and vertex operators are known exactly. These fixed points are nonperturbative and correspond to conformal invariant theories. The same phenomenon also happens in supersymmetric theories with the Yukawa type interactions.

hep-th↗

arXiv2002

Renormalization Properties of Softly Broken SUSY Gauge Theories

In the present review we show that renormalizations in a softly broken SUSY gauge theory are not independent but directly follow from those of an unbroken or rigid theory. This is a consequence of a treatment of a softly broken theory as a rigid one in external spurion superfield. This enables one to get the singular part of effective action in a broken theory from a rigid one by a simple modification of the couplings. Substituting the modified couplings into renormalization constants, RG equations, solutions to these equations, approximate solutions, fixed points, etc., one can get corresponding relations for the soft terms by a simple Taylor expansion over the Grassmannian variables. Some examples including the MSSM in low and high $\tanβ$ regime, SUSY GUTs and the N=2 Seiberg-Witten model are considered.

hep-ph↗

arXiv2002

Towards a Consistent SUSY QFT in Extra Dimensions

We consider N=1 SUSY gauge theory in six dimensions in components and show that provided the Dynkin indices of the matter fields representations satisfy the relation $\sum T(R)= C_2(G)$, the gauge sector is completely one-loop finite. In the matter sector the UV divergences form several invariant structures some of which are cancelled in physical amplitudes. Thus, the theory which is in general non-renormalizable may be consistent and even finite. Consequences for the SUSY GUT models in the bulk are briefly discussed.

hep-ph↗

arXiv2001

Renormalization of the Fayet-Iliopoulos Term in Softly Broken SUSY Gauge Theories

It is shown that renormalization of the Fayet-Iliopoulos term in a softly broken SUSY gauge theory, in full analogy with all the other soft terms renormalizations, is completely defined in a rigid or an unbroken theory. However, contrary to the other soft renormalizations, there is no simple differential operator that acts on the renormalization functions of a rigid theory and allows one to get the renormalization of the F-I term. One needs an analysis of the superfield diagrams and some additional diagram calculations in components. The method is illustrated by the four loop calculation of some part of renormalization proportional to the soft scalar masses and the soft triple couplings.

hep-ph↗

arXiv2001

A gobal fit to the anomalous magnetic moment, Higgs limit and b->s gamma in the constrained MSSM

New data on the anomalous magnetic moment of the muon together with the b->s gamma decay rate and Higgs limits are considered within the supergravity inspired constrained minimal supersymmetric model. We perform a global statistical chi2 analysis of these data and show that the allowed region of parameter space is bounded from below by the Higgs limit, which depends on the trilinear coupling and from above by the anomalous magnetic moment.

hep-ph↗

arXiv2001

A gobal fit to the anomalous magnetic moment, b->s gamma and Higgs limits in the constrained MSSM

New data on the anomalous magnetic moment a_mu of the muon together with the b->s gamma decay rate are considered within the supergravity inspired constrained minimal supersymmetric model. We perform a global statistical chi^2 analysis of these data and show that the allowed region of parameter space is bounded from below by the Higgs limit, which depends on the trilinear coupling and from above by the anomalous magnetic moment a_mu. The newest b->s gamma data deviate 1.7 sigma from recent SM calculations and prefer a similar parameter region as the 2.6 sigma deviation from a_mu.

hep-ph↗

arXiv2001

The b->sgamma rate and Higgs boson limits in the Constrained Minimal Supersymmetric Model

New NLO b->sgamma calculations have become available using resummed radiative corrections. Using these calculations we perform a global fit of the supergravity inspired constrained minimal supersymmetric model (CMSSM). We find that the resummed calculations show similar constraints as the LO calculations, namely that only with a relatively heavy supersymmetric mass spectrum of the order of 1 TeV the b-τYukawa unification and the b->sgamma rate can coexist in the large tanb scenario. The resummed b->sgamma calculations are found to reduce the renormalization scale uncertainty considerably. The low tanb scenario is excluded by the present Higgs limits from LEP II. The constraint from the Higgs limit in the $m_0,m_{1/2}$ plane is severe, if the trilinear coupling A_0 at the GUT scale is fixed to zero, but is considerably reduced for $A_0\le -2m_0$. The relatively heavy SUSY spectrum required by \besg corresponds to a Higgs mass of $m_h=119\pm 1~ (stop masses)}\pm 2~(theory)~\pm~3 (top mass) GeV $ in the CMSSM.

hep-ph↗

arXiv2001

MSSM Predictions of the neutral Higgs boson masses and LEP II production cross sections

Within the framework of the Minimal Supersymmetric Standard Model (MSSM) the Higgs masses and LEP II production cross sections are calculated for a wide range of the parameter space. In addition, the parameter space restricted by unification, electroweak symmetry breaking and other low energy constraints is considered in detail, in which case the masses of all SUSY partners can be estimated, so that their contributions to the radiative corrections can be calculated. Explicit analytical formulae for these contribution are derived. The radiative corrections from the Yukawa couplings of the third generation are found to dominate over the contributions from charginos and neutralinos. Large Higgs mass uncertainties are due to the top mass uncertainty and the unknown sign of the Higgs mixing parameter. For the low tanb scenario the mass of the lightest Higgs is found to be below 103 GeV for a top mass below 190 GeV. The cross section at a LEP energy of 192 GeV is sufficient to find or exclude this low tanb scenario for a top mass below 180 GeV. For the high tanb scenario only a small fraction of the parameter space can be covered, since the Higgs mass is predicted between 105 and 125 GeV in most cases. At the theoretically possible LEP II energy of 205 GeV part of the parameter space for the large tanb scenario would be accessible.

hep-ph↗

arXiv2001

Beyond the Standard Model (In Search of Supersymmetry)

The present lectures contain an introduction to low energy supersymmetry, a new symmetry that relates bosons and fermions, in particle physics. The Standard Model of fundamental interactions is briefly reviewed, and the motivation to introduce supersymmetry is discussed. 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 MSSM as well as possible experimental signatures of SUSY are described. An intriguing situation with the supersymmetric Higgs boson is discussed.

hep-ph↗

arXiv2000

Massive Ghosts in Softly Broken SUSY Gauge Theories

It is shown that, due to soft supersymmetry breaking in gauge theories within the superfield formalism, there appears the mass for auxiliary gauge fields. It enters into the RG equations for soft masses of physical scalar particles and can be eliminated by solving its own RG equation. Explicit solutions up to the three-loop order in the general case and in the MSSM are given. The arbitrariness in choosing the initial condition is discussed.

hep-ph↗

arXiv2000

The b->sgamma decay rate in NLO, Higgs boson limits, and LSP masses in the CMSSM

New NLO b->sgamma calculations have become available. We observe that at large tanbeta the dominant NLO term of the chargino amplitude, which is proportional to mu.tanbeta^2, changes the sign of this amplitude in a large region of the CMSSM parameter space, so that the preferred sign of the Higgs mixing parameter mu now agrees with the preferred sign of b-tau unification. We find that the b->sgamma rate does not constrain the CMSSM anymore, if the higher order contributions and its uncertainties from the incomplete calculations are taken into account. The Higgs boson mass in the CMSSM is found to be between 110 and 120 GeV for a top mass of 175 GeV, if the Higgs mass limit of 107.9 GeV from LEP, which implies tanbeta>3.3, is taken into account The mean Higgs boson mass value and its dominant errors are: m_h=115\pm 3(stop mass) \pm 1.5(stop mixing) \pm 2(theory) \pm 5(top mass) GeV. This Higgs mass range is valid for all tanbeta values above 20 and decreases for lower tanbeta. If the presently claimed evidence for dark matter by the DAMA Collaboration is interpreted as the Lightest Supersymmetric Particle (LSP) of the CMSSM, then it is at the edge of the parameter space allowed by the present Higgs limit of 107.9 GeV from LEP.

hep-ph↗

arXiv2000

Approximate Analytic Solutions of RG Equations for Yukawa and Soft Couplings in SUSY Models

We present simple analytical formulae which describe solutions of the RG equations for Yukawa couplings in SUSY gauge theories with the accuracy of a few per cent. Performing the Grassmannian expansion in these solutions one finds those for all the soft couplings and masses. The solutions clearly exhibit the fixed point behaviour which can be calculated analytically. A comparison with numerical solutions is demonstrated.

hep-ph↗

arXiv2000

Supersymmetry in Particle Physics: The Renormalization Group Viewpoint

An attempt is made to present modern hopes to find manifestation of supersymmetry, a new symmetry that relates bosons and fermions, in particle physics from the point of view of renormalization group flow. The Standard Model of particle interactions is briefly reviewed, the main notions of supersymmetry are introduced. In more detail the RG flow in the Minimal Supersymmetric Standard Model is considered. Predictions of particle spectrum are obtained based on the RG fixed points.

hep-ph↗

arXiv1999

Infrared Quasi Fixed Points and Mass Predictions in the MSSM II: Large tan(beta) Scenario

We consider the infrared quasi fixed point solutions of the renormalization group equations for the Yukawa couplings and soft supersymmetry breaking parameters in the MSSM in the \underline{large $\tanβ$} regime. The existence of IR quasi fixed points together with the values of gauge couplings, third generation quarks, lepton and Z-boson masses allows one to predict masses of the Higgs bosons and SUSY particles as functions of the only free parameter, $m_{1/2}$, or the gluino mass. The lightest Higgs boson mass for $M_{SUSY} \approx 1$ TeV is found to be $m_h=128.2-0.4-7.1 \pm 5$ GeV for $μ>0$ and $m_h=120.6-0.1-3.8 \pm 5$ GeV for $μ<0$.

hep-ph↗

arXiv1999

The Higgs Boson: Shall We See It Soon Or Is It Still Far Away?

The status of the Higgs boson mass in the Standard Model and its supersymmetric extensions is reviewed and the perspectives of Higgs searches are discussed. The parameter space of the Minimal Supersymmetric Standard Model (MSSM) is analysed with the emphasis on the lightest Higgs mass. The infrared behaviour of renormalization group equations for the parameters of MSSM is examined and infrared quasi-fixed points are used for the Higgs mass predictions. They strongly suggest the Higgs mass to be lighter than 100 or 130 GeV for low and high $\tanβ$ scenarios, respectively. Extended models, however, allow one to increase these limits for low $\tanβ$ up to 50%.

hep-ph↗

arXiv1999

Infrared Quasi Fixed Points and Mass Predictions in the MSSM

We consider the infrared quasi-fixed point solutions of the renormalization group equations for the top-quark Yukawa coupling and soft supersymmetry breaking parameters in the MSSM. The IR quasi-fixed points together with the values of the gauge couplings, the top-quark and Z-boson masses allow one to predict masses of the Higgs bosons, the stop squarks and the lightest chargino as functions of the only free parameter $m_{1/2}$ or the gluino mass. The mass of the lightest Higgs boson for $μ>0$ and $M_{SUSY} \approx 1$ TeV is found to be $m_h=(94.3+1.6+0.6\pm5\pm0.4)$ GeV. The case with $μ<0$ is excluded by experimental data.

hep-ph↗

arXiv1998

Exploring Softly Broken SUSY Theories via Grassmannian Taylor Expansion

We demonstrate that soft SUSY breaking introduced via replacement of the couplings of a rigid theory by spurion superfields has far reaching consequences. Substituting these modified couplings into renormalization constants, RG equations, solutions to these equations, fixed points, finiteness conditions, etc., one can get corresponding relations for the soft terms by a simple Taylor expansion over the Grassmannian variables. This way one can get new solutions of the RG equations. Some examples including the MSSM, SUSY GUTs and the N=2 Seiberg-Witten model are given.

hep-ph↗

arXiv1998

Exact Results in Renormalization of Softly Broken SUSY Gauge Theories

It is shown that softly broken theory is equivalent to a rigid theory in external spurion superfield. The singular part of effective action in a broken theory follows from a rigid one by a simple redefinition of the couplings. This gives an explicit relation between the soft and rigid couplings renormalizations. As an illustration the renormalization group functions in the MSSM have been calculated. The method opens a possibility to construct a totally all loop finite N=1 SUSY gauge theory, including the soft SUSY breaking terms. Explicit relations between the soft terms, which lead to a completely finite theory in any loop order, are given.

hep-ph↗