arXiv subjects

D. I. Kazakov

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

At least 37 records · Page 2Linked to original sources

arXiv2019

RG Equations and High Energy Behaviour in Non-Renormalizable Theories

We suggest a novel view on non-renormalizable interactions. It is based on the usual BPHZ R-operation which is equally applicable to any local QFT independently whether it is renormalizable or not. As a playground we take the phi^4_D theory in D dimensions for D=4,6,8,10 and consider the four-point scattering amplitude on shell. We derive the generalized RG equation and find the solution valid for any D that sums up the leading logarithms in all orders of PT in full analogy with the renormalizable case. It is found that the scattering amplitude in the phi^4_D theory possesses the Landau pole at high energy for any D. We discuss the application of the proposed procedure to other non-renormalizable theories.

hep-th↗

arXiv2019

High Energy Behaviour in Maximally Supersymmetric Gauge Theories in Various Dimensions

Maximally supersymmetric field theories in various dimensions are believed to possess special properties due to extended supersymmetry. In four dimensions they are free from UV divergences but are IR divergent on shell, in higher dimensions, on the contrary, they are IR finite but UV divergent. In what follows we consider the four-point on-shell scattering amplitudes in D=6,8,10 supersymmetric Yang-Mills theory in the planar limit within the spinor-helicity and on shell supersymmetric formalism. We study the UV divergences and demonstrate how one can sum them over all orders of PT. Analyzing the R-operation we obtain the recursive relations and derive differential equations that sum all leading, subleading, etc., divergences in all loops generalizing the standard RG formalism for the case of nonrenormalizable interactions. We then perform the renormalization procedure which differs from the ordinary one in that the renormalization constant becomes the operator depending on kinematics. Solving the obtained RG equations for particular sets of diagrams analytically and for the general case numerically, we analyze their high energy behaviour and find out that while each term of PT increases as a power of energy the total sum behaves differently: in D=6 two partial amplitudes decrease with energy and the third one increases exponentially, while in D=8 and 10 the amplitudes possess an infinite number of periodic poles at finite energy.

hep-th↗

arXiv2018

Can we discover a light singlet-like NMSSM Higgs boson at the LHC?

In the next-to minimal supersymmetric standard model (NMSSM) one additional singlet-like Higgs boson with small couplings to standard model (SM) particles is introduced. Although the mass can be well below the discovered 125 GeV Higgs boson mass its small couplings may make a discovery at the LHC difficult. We use a novel scanning technique to efficiently scan the whole parameter space and determine the range of cross sections and branching ratios for the light singlet-like Higgs boson below 125 GeV. This allows to determine the perspectives for the future discovery potential at the LHC. Specific LHC benchmark points are selected representing the salient NMSSM features.

hep-ph↗

arXiv2018

The Structure of UV Divergences in Maximally Supersymmetric Gauge Theories

We consider the UV divergences up to sub-sub leading order for the four-point on-shell scattering amplitudes in D=8 supersymmetric Yang-Mills theory in the planar limit. We trace how the leading, subleading, etc divergences appear in all orders of perturbation theory. The structure of these divergences is typical for any local quantum field theory independently on renormalizability. We show how the generalized RG equations allow one to evaluate the leading, subleading, etc. contributions in all orders of PT starting from one-, two-, etc. loop diagrams respectively. We focus then on subtraction scheme dependence of the results and show that in full analogy with renormalizable theories the scheme dependence can be absorbed into the redefinition of the couplings. The only difference is that the role of the couplings play dimensionless combinations like g^2s^2 or g^2t^2, where s and t are the Mandelstam variables.

hep-th↗

arXiv2017

Perspectives of direct Detection of supersymmetric Dark Matter in the NMSSM

In the Next-to-Minimal-Supersymmetric-Standard-Model (NMSSM) the lightest supersymmetric particle (LSP) is a candidate for the dark matter (DM) in the universe. It is a mixture from the various gauginos and Higgsinos and can be bino-, Higgsino- or singlino-dominated. Singlino-dominated LSPs can have very low cross sections below the neutrino background from coherent neutrino scattering which is limiting the sensitivity of future direct DM search experiments. However, previous studies suggested that the combination of both, the spin-dependent (SD) and spin-independent (SI) searches are sensitive in complementary regions of parameter space, so considering both searches will allow to explore practically the whole parameter space of the NMSSM. In this letter, the different scenarios are investigated with a new scanning technique, which reveals that significant regions of the NMSSM parameter space cannot be explored, even if one considers both, SI and SD, searches.

hep-ph↗

arXiv2017

Summation of all-loop UV Divergences in Maximally Supersymmetric Gauge Theories

We consider the leading and subleading UV divergences for the four-point on-shell scattering amplitudes in D=6,8,10 supersymmetric Yang-Mills theories in the planar limit. These theories belong to the class of maximally supersymmetric gauge theories and presumably possess distinguished properties beyond perturbation theory. In the previous works, we obtained the recursive relations that allow one to get the leading and subleading divergences in all loops in a pure algebraic way. The all loop summation of the leading divergences is performed with the help of the differential equations which are the generalization of the RG equations for non-renormalizable theories. Here we mainly focus on solving and analyzing these equations. We discuss the properties of the obtained solutions and interpretation of the results.

hep-th↗

arXiv2017

Leading and Subleading UV Divergences in Scattering Amplitudes for D=8 N=1 SYM Theory in All Loops

We consider the leading and subleading UV divergences for the four-point on-shell scattering amplitudes in D=8 N=1 sypersymmetric Yang-Mills theory within the spinor-helicity and superfield formalism. This theory belongs to the class of maximally supersymmetric gauge theories and presumably possesses distinguished properties beyond perturbation theory. We obtain the recursive relations that allow one to get the leading and subleading divergences in all loops in a pure algebraic way staring from the one loop (for the leading poles) and two loop (for the subleading ones) diagrams. As a particular example where the recursive relations have a simple form we consider the ladder type diagrams. The all loop summation of the leading and subleading divergences is performed with the help of the differential equations which are the generalization of the RG equations for non-renormalizable theories. They have explicit solutions for the ladder type diagrams. We discuss the properties of the obtained solutions and interpretation of the results.

hep-th↗

arXiv2016

Higgs Branching Ratios in Constrained Minimal and Next-to-Minimal Supersymmetry Scenarios Surveyed

In the CMSSM the heaviest scalar and pseudo-scalar Higgs bosons decay largely into b-quarks and tau-leptons because of the large $\tanβ$ values favored by the relic density. In the NMSSM the number of possible decay modes is much richer. In addition to the CMSSM-like scenarios, the decay of the heavy Higgs bosons is preferentially into top quark pairs (if kinematically allowed), lighter Higgs bosons or neutralinos, leading to invisible decays. We provide a scan over the NMSSM parameter space to project the 6D parameter space of the Higgs sector on the 3D space of the Higgs masses to determine the range of branching ratios as function of the Higgs boson mass for all Higgs bosons. Specific LHC benchmark points are proposed, which represent the salient NMSSM features.

hep-ph↗

arXiv2016

SUSY Production at the LHC without Missing P_T

We consider relatively rare events of SUSY production at the LHC without missing $p_T$. Namely, we discuss the chargino production with further decay into the W-boson and the neutralino when the masses of chargino and neutralino differ by 80-90 GeV. In this case, in the final state one has two Ws and missing $E_T$ but no missing $P_T$. The produced neutralinos are just busted along Ws. Within the MSSM such events are quite probable in the region of parameter space close to the EWSB border line. The excess in the W production cross-section may achieve a few \%.

hep-ph↗

arXiv2016

SUSY at the LHC without Missing P_T

We consider a specific class of events of the SUSY particle production at the LHC without missing p_T. Namely, we discuss the chargino pair production with a further decay into the W-boson and the neutralino when the masses of the chargino and neutralino differ by 80-90 GeV. In this case, in the final state one has two Ws and missing E_T but no missing P_T. The produced neutralinos are just boosted along Ws. For a demonstration we consider the MSSM with non-universal gaugino masses. In this case, such events are quite probable in the region of parameter space where the lightest chargino and neutralino are mostly gauginos. The excess in the W production cross-section reach about 10 % over the Standard Model background. We demonstrate that the LHC experiments, which presently measure the WW production cross section at the 8 % level can probe chargino mass around 110 GeV within the suggested scenario, which is not accessible via other searches. If the precision of WW cross section measurement at the LHC will achieve the 3 % level, then it would probe chargino masses up to about 150 GeV within the no missing P_T scenario.

hep-ph↗

arXiv2015

Landscape View at the Edge of a Mystery

The situation in particle physics after the discovery of the Higgs boson is discussed. Is the Standard Model consistent quantum field theory? Does it describe all experimental data? Are there any indications of physics beyond the SM? Is there another scale except for the EW and the Planck ones? Is the SM of particles physics compatible with Cosmology? New challenges of hadron physics: exotic hadrons and dense hadronic matter. Search for new physics, from the Higgs sector to dark matter, supersymmetry, extra dimensions and compositeness. What do we expect? What are the main targets? We try to answer the main questions and describe the key issues of possible new physics beyond the SM.

hep-ph↗

arXiv2015

Divergences in maximal supersymmetric Yang-Mills theories in diverse dimensions

The main aim of this paper is to study the scattering amplitudes in gauge field theories with maximal supersymmetry in dimensions D=6,8 and 10. We perform a systematic study of the leading ultraviolet divergences using the spinor helicity and on-shell momentum superspace framework. In D=6 the first divergences start at 3 loops and we calculate them up to 5 loops, in D=8,10 the first divergences start at 1 loop and we calculate them up to 4 loops. The leading divergences in a given order are the polynomials of Mandelstam variables. To be on the safe side, we check our analytical calculations by numerical ones applying the alpha-representation and the dedicated routines. Then we derive an analog of the RG equations for the leading pole that allows us to get the recursive relations and construct the generating procedure to obtain the polynomials at any order of (perturbation theory) PT. At last, we make an attempt to sum the PT series and derive the differential equation for the infinite sum. This equation possesses a fixed point which might be stable or unstable depending on the kinematics. Some consequences of these fixed points are discussed.

hep-th↗

arXiv2014

The impact of a 126 GeV Higgs on the neutralino mass

We highlight the differences of the dark matter sector between the constrained minimal supersymmetric SM (CMSSM) and the next-to-minimal supersymmetric SM (NMSSM) including the 126 GeV Higgs boson using GUT scale parameters. In the dark matter sector the two models are quite orthogonal: in the CMSSM the WIMP is largely a bino and requires large masses from the LHC constraints. In the NMSSM the WIMP has a large singlino component and is therefore independent of the LHC SUSY mass limits. The light NMSSM neutralino mass range is of interest for the hints concerning light WIMPs in the Fermi data. Such low mass WIMPs cannot be explained in the CMSSM. Furthermore, prospects for discovery of XENON1T and LHC at 14 TeV are given.

hep-ph↗

arXiv2014

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.

hep-th↗

arXiv2014

Evaluation of Multi-Box Diagrams in Six Dimensions

We present a simple method which simplifies the evaluation of the on-shell multiple box diagrams reducing them to triangle type ones. For the $L$-loop diagram one gets the expression in terms of Feynman parameters with $2L$-fold integration. As examples we consider the 2 and 3 loops cases, the numerical integration up to six loops is also presented. The method is valid in six dimensions where neither UV not IR divergences appear.

hep-th↗

arXiv2013

A comparison of the Higgs sectors of the CMSSM and NMSSM for a 126 GeV Higgs boson

The recent discovery of a Higgs-like boson at the LHC with a mass of 126 GeV has revived the interest in supersymmetric models, which predicted a Higgs boson mass below 130 GeV long before its discovery. We compare systematically the allowed parameter space in the constrained Minimal Supersymmetric Standard Model (CMSSM) and the Next-to-Minimal Supersymmetric Model (NMSSM) by minimizing the chi^2 function with respect to all known constraints from accelerators and cosmology using GUT scale parameters. For the CMSSM the Higgs boson mass at tree level is below the Z^0 boson mass and large radiative corrections are needed to obtain a Higgs boson mass of 126 GeV, which requires stop squark masses in the multi-TeV range. In contrast, for the NMSSM light stop quarks are allowed, since in the NMSSM at tree level the Higgs boson mass can be above the Z^0 boson mass from mixing with the additional singlet Higgs boson. Predictions for the scalar boson masses are given in both models with emphasis on the unique signatures of the NMSSM, where the heaviest scalar Higgs boson decays in the two lighter scalar Higgs bosons with a significant branching ratio, in which case one should observe double Higgs boson production at the LHC. Such a signal is strongly suppressed in the CMSSM. In addition, since the LSP is higgsino-like, Higgs boson decays into LSPs can be appreciable, thus leading to invisible Higgs decays.

hep-ph↗

arXiv2013

On the amplitudes in N=(1,1) D=6 SYM

We consider the on-shell amplitudes in N=(1,1) SYM in D=6 dimensions within the spinor helicity and on-shell superspace formalism. This leads to an effective and straightforward technique reducing the calculation to a set of scalar master integrals. As an example, the simplest four point amplitude is calculated in one and two loops in the planar limit. All answers are UV and IR finite and expressed in terms of logs and Polylogs of transcendentality level 2 at one loop, and 4 and 3 at two loops. The all loop asymptotical limit at high energy is obtained which exhibits the Regge type behaviour. The intercept is calculated in the planar limit and is equal to alpha(t)=1+\sqrt{g_{YM}^2 N_c|t|/32pi^3}.

hep-th↗

arXiv2013

SUSY Phenomenology today

The review of the SUSY phenomenology today is given with the emphasis on generic properties of SUSY models, SUSY searches at the LHC and in astrophysics. Due to the absence of any definite SUSY signal at accelerators and other experiments, we describe the allowed regions in the MSSM and NMSSM parameter space and discuss the possibilities of SUSY manifestation in the near future.

hep-ph↗