arXiv subjects

D. I. Kazakov

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

105 records · Page 6Linked to original sources

arXiv1998

Higgs Limit and b->s gamma Constraints in Minimal Supersymmetry

New limits on the Higgs mass from LEP and new calculations on the radiative (penguin) decay of the b->s gamma branching ratio restrict the parameter space of the Constrained Minimal Supersymmetric Standard Model (CMSSM). We find that for the low tan(beta) scenario only one sign of the Higgs mixing parameter is allowed, while the high tan(beta scenario is practically excluded, if one requires all sparticles to be below 1 TeV and imposes radiative electroweak symmetry breaking as well as gauge and Yukawa coupling unification. For squarks between 1 and 2 TeV high tan(beta) scenarios are allowed. We consider especially a new high tan(beta)=64 scenario with triple unification of all Yukawa couplings of the third generation, which show an infrared fixed point behaviour. The upper limit on the mass of the lightest Higgs in the low (high) tan(beta) scenarios is 97+-6~(120+-2) GeV, where the errors originate predominantly from the uncertainty in the top mass.

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arXiv1998

Updated Combined Fit of Low Energy Constraints to Minimal Supersymmetry

The new precise LEP measurements of alphas and the electroweak mixing angle as well as the new LEP II mass limits for supersymmetric particles and new calculations for the radiative (penguin) decay of the b-quark into sgamma allow a further restriction in the parameter space of the Constrained Minimal Supersymmetric Standard Model (CMSSM).

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arXiv1997

Finiteness of Soft Terms in Finite N=1 SUSY Gauge Theories

Recently proposed relations between the renormalization group functions of the soft supersymmetry breaking terms and those of a rigid theory allow one to consider a possibility of constructing a totally all loop finite N=1 SUSY gauge theory, including the soft SUSY breaking terms. The requirement of finiteness, which can be satisfied in previously constructed finite SUSY GUTs, imposes some constraints on the SUSY breaking parameters which, in the leading order, coincide with those originating from the supergravity and superstring-inspired models. Explicit relations between the soft terms, which lead to a completely finite theory in any loop order, are given.

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arXiv1997

Renormalizations in Softly Broken SUSY Gauge Theories

The supergraph technique for calculations in supersymmetric gauge theories where supersymmetry is broken in a "soft" way (without introducing quadratic divergencies) is reviewed. By introducing an external spurion field the set of Feynman rules is formulated and explicit connections between the UV counterterms of a softly broken and rigid SUSY theories are found. It is shown that the renormalization constants of softly broken SUSY gauge theory also become external superfields depending on the spurion field. Their explicit form repeats that of the constants of a rigid theory with the redefinition of the couplings. The method allows us to reproduce all known results on the renormalization of soft couplings and masses in a softly broken theory. As an example the renormalization group functions for soft couplings and masses in the Minimal Supersymmetric Standard Model up to the three-loop level are calculated.

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arXiv1997

On calculation of the off-shell renormalization functions in the R^2 gravity

A new way how to calculate the off-shell renormalization functions within the $R^2$-gravity has been proposed. The one-loop renormalization group equations in the approach suggested have been constructed. The behaviour of effective potential for an massless scalar field interacting with the quantum gravitational field has been analyzed in this approach.

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arXiv1996

Noninvariant renormalization in the background-field method

We investigate the consistency of the background-field formalism when applying various regularizations and renormalization schemes. By an example of a two-dimensional $σ$ model it is demonstrated that the background-field method gives incorrect results when the regularization (and/or renormalization) is noninvariant. In particular, it is found that the cut-off regularization and the differential renormalization belong to this class and are incompatible with the background-field method in theories with nonlinear symmetries.

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arXiv1996

Softly Broken Finite Supersymmetric Grand Unified Theory

In the context of the standard SUSY GUT scenario, we present a detailed analysis of the softly broken finite supersymmetric grand unified theory. The model, albeit non-minimal, remains very rigid due to the requirement of finiteness. It is based on the $SU(5)$ gauge group and is UV finite to all orders of perturbation theory. It contains three generations of the matter fields together with four pairs of Higgses. The requirement of UV finiteness fixes all the Yukawa couplings at the GUT scale. Imposing the condition of universality on the soft couplings at the Planck scale and then extending the condition of finiteness to them, one gets a completely finite unified theory above $M_{GUT}.$ This makes the fine-tuning procedure more meaningful and leads to the usual Minimal Supersymmetric Standard Model below $M_{GUT}$. All the masses of the ordinary particles including Higgses are obtained due to the Higgs mechanism at the electro-weak scale. The hierarchy of quark and lepton masses is related to that of v.e.v.'s of the Higgs fields and is governed by the Higgs mixing matrix in the generation space. Superpartners develop their masses according to the RG equations starting from the soft terms at the Planck scale. The suggestion of complete finiteness and maximal simplicity of the unified theory leads to the connection between the initial values of soft SUSY breaking parameters, namely $m_0^2=1/3m_{1/2}^2,\ A_t=A_b=A_τ=-m_{1/2}, \ B=-m_{1/2}$, so that the number of free parameters is less than that of the MSSM.

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arXiv1996

Combined Fit of Low Energy Constraints to Minimal Supersymmetry and Discovery Potential at LEP II

Within the Constrained Minimal Supersymmetric Standard Model it is possible to predict the low energy gauge couplings and masses of the 3. generation particles from a few parameters at the GUT scale. In addition the MSSM predicts elektroweak symmetry breaking due to large radiative corrections from Yukawa couplings, thus relating the Z^0 boson mass to the top quark mass. From a χ^2 analysis, in which these constraints can be considered simultaneously, one can calculate the probability for each point in the MSGUT parameter space. Our fits include full second order corrections for the gauge and Yukawa couplings, low energy treshold effects, contributions of all (s)particles to the Higgs potential and corrections to m_b from qluinos and higgsinos, which exclude (in our notation) positive values of the mixing parameter in the Higgs potential μfor the large tan βregion. Further constraints can be derived from the branching ratio for the radiative (penguin) decay of the b-quark into s γand the lower limit on the lifetime of the universe, which requires the dark matter density due to the Lightest Supersymmetric Particle (LSP) not to overclose the universe. For particles, which are most likely to have masses in the LEP II energy range, the cross sections are given for the various energy scenarios at LEP II. For low tan βthe production of the lightest Higgs boson, which is expected to have a mass below 103 GeV, is the most promising channel, while for large tan βthe production of charginos and/or neutralinos covers the preferred parameter space.

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arXiv1994

The Background-Field Method and Noninvariant Renormalization

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arXiv1994

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.

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arXiv1994

Is the stop mass below the top mass?

It is shown that a top mass of 174+/-17 GeV, as quoted recently by the CDF Collaboration, constrains the mixing angle between the Higgs doublets in the Minimal Supersymmmetric extension of the Standard Model (MSSM) to: 1.2<tan beta<5.5 at the 90% C.L.. The most probable value corresponds to tan beta = 1.56; such a small value causes a large mixing in the stop sector and the lightest stop is likely to be below the top mass. In this case the stop production in pp_bar collisions would contribute to the top signature, thus providing a possible explanation for the large effective tt_bar cross section observed by CDF.

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arXiv1994

On a Possible Explanation of the Origin of the Quark Mass Spectrum

Contrary to the usual case when the quark mass spectrum is defined by that of the quark Yukawa couplings while the vacuum expectation value of the Higgs field remains universal, we suggest to consider the opposite situation. Each generation of quarks and leptons is associated with its own Higgs doublet, while the Yukawa couplings are the same. This situation naturally arises in the framework of finite supersymmetric Grand Unification scenario. Nondegeneracy of the quark mass spectrum is then due to asymmetric vacuum expectation values which spontaneously break the discrete flavour symmetry in the Higgs sector.

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arXiv1993

On Quantum Deformation of the Schwarzschild Solution

We consider the deformation of the Schwarzschild solution in general relativity due to spherically symmetric quantum fluctuations of the metric and the matter fields. In this case, the 4D theory of gravity with Einstein action reduces to the effective two-dimensional dilaton gravity. We have found that the Schwarzschild singularity at $r=0$ is shifted to the finite radius $r_{min} \sim r_{Pl}$, where the scalar curvature is finite, so that the space-time looks regular and consists of two asymptotically flat sheets glued at the hypersurface of constant radius.

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arXiv1993

Constraints on SUSY Masses in Supersymmetric Grand Unified Theories

Within the Minimal Supersymmetric Grand Unified Theory (MSGUT) masses of the predicted supersymmetric particles are constrained by the world averaged values of the electroweak and strong coupling constants, the lower limits on the proton lifetime,the lower limit on the lifetime of the universe, which implies an upper limit on the dark matter density, the electroweak symmetry breaking originating from radiative corrections due to the heavy top quark, and the ratio of the masses of the b-quark and tau-lepton. A combined fit shows that indeed the MSGUT model can satisfy all these constraints simultaneously and the corresponding values for all SUSY masses are given within the minimal model, taking into account the complete second order renormalisation group equations for the couplings and the one-loop corrections to the Higgs potential for the calculation of the Z-mass and the Higgs masses. These one-loop corrections to MZ have been derived explicitly as function of the stop- and top masses and found to be small for the best solution, but unnaturally large for the 90% C.L. upper limits on the SUSY masses.

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arXiv1993

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 $\tilde{R}$ operation. Two-dimensional $σ$ models and the four-dimensional $ϕ^4$ 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 $\tilde{R}$ operation in a self-consistent way, as the original recipe does the ultraviolet $R$ operation.

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