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K. Melnikov

Publications and source records attributed to K. Melnikov.

At least 19 recordsLinked to original sources
arXiv2014

Planning the Future of U.S. Particle Physics (Snowmass 2013): Chapter 3: Energy Frontier

These reports present the results of the 2013 Community Summer Study of the APS Division of Particles and Fields ("Snowmass 2013") on the future program of particle physics in the U.S. Chapter 3, on the Energy Frontier, discusses the program of research with high-energy colliders. This area includes experiments on the Higgs boson, the electroweak and strong interactions, and the top quark. It also encompasses direct searches for new particles and interactions at high energy.

hep-ex↗
arXiv2014

Higgs Working Group Report of the Snowmass 2013 Community Planning Study

This report summarizes the work of the Energy Frontier Higgs Boson working group of the 2013 Community Summer Study (Snowmass). We identify the key elements of a precision Higgs physics program and document the physics potential of future experimental facilities as elucidated during the Snowmass study. We study Higgs couplings to gauge boson and fermion pairs, double Higgs production for the Higgs self-coupling, its quantum numbers and $CP$-mixing in Higgs couplings, the Higgs mass and total width, and prospects for direct searches for additional Higgs bosons in extensions of the Standard Model. Our report includes projections of measurement capabilities from detailed studies of the Compact Linear Collider (CLIC), a Gamma-Gamma Collider, the International Linear Collider (ILC), the Large Hadron Collider High-Luminosity Upgrade (HL-LHC), Very Large Hadron Colliders up to 100 TeV (VLHC), a Muon Collider, and a Triple-Large Electron Positron Collider (TLEP).

hep-ex↗
arXiv2013

Handbook of LHC Higgs Cross Sections: 3. Higgs Properties

This Report summarizes the results of the activities in 2012 and the first half of 2013 of the LHC Higgs Cross Section Working Group. The main goal of the working group was to present the state of the art of Higgs Physics at the LHC, integrating all new results that have appeared in the last few years. This report follows the first working group report Handbook of LHC Higgs Cross Sections: 1. Inclusive Observables (CERN-2011-002) and the second working group report Handbook of LHC Higgs Cross Sections: 2. Differential Distributions (CERN-2012-002). After the discovery of a Higgs boson at the LHC in mid-2012 this report focuses on refined prediction of Standard Model (SM) Higgs phenomenology around the experimentally observed value of 125-126 GeV, refined predictions for heavy SM-like Higgs bosons as well as predictions in the Minimal Supersymmetric Standard Model and first steps to go beyond these models. The other main focus is on the extraction of the characteristics and properties of the newly discovered particle such as couplings to SM particles, spin and CP-quantum numbers etc.

hep-ph↗
arXiv2008

Masses, fermions and generalized D-dimensional unitarity

We extend the generalized D-dimensional unitarity method for numerical evaluation of one-loop amplitudes by incorporating massive particles. The issues related to extending the spinor algebra to higher dimensions, treatment of external self-energy diagrams and mass renormalization are discussed within the context of the D-dimensional unitarity method. To validate our approach, we calculate in QCD the one-loop scattering amplitudes of a massive quark pair with up to three additional gluons for arbitrary spin states of the external quarks and gluons.

hep-ph↗
arXiv2002

Relating bottom quark mass in DR-bar and MS-bar regularization schemes

The value of the bottom quark mass at M_Z in the DR-bar scheme is an important input for the analysis of supersymmetric models with a large value of tan(beta). Conventionally, however, the running bottom quark mass extracted from experimental data is quoted in the MS-bar scheme at the bottom mass scale. We describe a two loop procedure for the conversion of the bottom quark mass from MS-bar to DR-bar scheme. The Particle Data Group value m_b(m_b) = 4.2 \pm 0.2 GeV in the MS-bar scheme corresponds to a range of 2.65-3.03 GeV for m_b(M_Z) in the DR-bar scheme.

hep-ph↗
arXiv2000

Top-Antitop Pair Production close to Threshold: Synopsis of recent NNLO Results

Using non-relativistic effective theories, new next-to-next-to-leading order (NNLO) QCD corrections to the total $t\bar t$ production cross section at the Linear Collider have been calculated recently. In this article the NNLO calculations of several groups are compared and the remaining uncertainties are discussed. The theoretical prospects for an accurate determination of top quark mass parameters are discussed in detail. An outlook on possible future improvements is given.

hep-ph↗
arXiv2000

Contribution of the direct decay $ϕ\toπ^+ π^- γ$ to the process $e^+ e^- \to π^+ π^- γ$ at DA$Φ$NE

The potential of DAPHNE to explore direct radiative decay $ϕ\to π^+ π^- γ$ is studied in detail. Predictions of different theoretical models for this decay are compared. We find that it should be possible to discriminate between these models at DAPHNE in one year, even assuming a relatively low luminosity ${\cal{L}} = 10^{31} {\rm cm}^{-2} {\rm sec^{-1}}$. The influence of the decay $ϕ\to π^+ π^- γ$ on the measurement of total cross section $σ(e^+e^- \to {\rm hadrons})$ by tagging a photon in the reaction $e^+e^- \to π^+π^- γ$ is also discussed.

hep-ph↗
arXiv1999

Measuring sigma(e^+e^- \to hadrons) using tagged photon

We propose to use events with radiated photons in e^+e^- collisions to measure the total cross section of e^+ e^- \to hadrons as a function of the center of mass energy. The Monte Carlo simulation for the collider DAPHNE shows that a competitive accuracy can be achieved with this method.

hep-ph↗
arXiv1998

Positronium hyperfine splitting: analytical value at m*alpha^6

We present an analytic calculation of the m*alpha^6 recoil corrections to the hyperfine splitting (HFS) of the ground state energy levels in positronium. We find ΔE_{\rm rec} = m alpha^6 (-1/6 ln(alpha) + 331/432 -ln(2)/4 - 17 Zeta(3)/(8 pi^2) + 5/(12 pi^2)) \approx m alpha^6 (- 1/6 ln(alpha) + 0.37632), confirming Pachucki's numerical result \cite{Ph}. We present a complete analytic formula for the m*alpha^6 HFS of the positronium ground state and, including m*alpha^7*ln^2(alpha) effects, find E(1^3S_1)-E(1^1S_0))_{theory} = 203 392(1) MHz. This differs from the experimental results by about 3 standard deviations.

hep-ph↗
arXiv1996

Final state interaction in the production of heavy unstable particles

We make an attempt to discuss in detail the effects originating from the final state interaction in the processes involving production of unstable elementary particles and their subsequent decay. Two complementary scenarios are considered: the single resonance production and the production of two resonances. We argue that part of the corrections due to the final state interaction can be connected with the Coulomb phases of the involved charge particles; the presence of the unstable particle in the problem makes the Coulomb phase ``visible''. It is shown how corrections due to the final state interaction disappear when one proceeds to the total cross-sections. We derive one-loop non-factorizable radiative corrections to the lowest order matrix element of both single and double resonance production. We discuss how the infrared limit of the theories with the unstable particles is modified. In conclusion we briefly discuss our results in the context of the forthcoming experiments on the $W^+W^-$ and the $t\bar t$ production at LEP $2$ and NLC.

hep-ph↗
arXiv1996

Physical mechanism of the linear beam-size effect at colliders

We present qualitative but precise description of the linear beam-size effect predicted for the processes in which unstable but long--living particles collide with each other. We derive physically pronounced equation for the events rate which proves that the linear beam-size effect corresponds to the scattering of one beam of particles on the decay products of the other. We compare this linear beam-size effect with the known logarithmic beam-size effect measured in the experiments on a single bremsstrahlung at VEPP-4 and HERA.

hep-ph↗
arXiv1996

Processes with the $t$-channel singularity in the physical region: finite beam sizes make cross sections finite

It is known that some high-energy processes have a $t$-channel singularity in the physical region. In this paper we show that this singularity is regularized if one takes into account the finite sizes of the colliding beams, i.e. the realistic situation which takes place at high--energy colliders. On this way we obtain the finite cross section which is linear proportional to the transverse sizes of the colliding beams. As an application of the above result we study the production of the single $W$ boson at $μ^+μ^-$ colliders in the reaction $μ^- μ^+ \to e \bar ν_e W^+ $. For the total energy $\sqrt {s}\approx 95$ GeV and reasonable parameters of the muon beams the ``beam--size '' dependent part of the cross section for this reaction is of the order of the standard cross section of the $μ^- μ^+ \to μ^- \bar ν_μ W^+ $ process.

hep-ph↗
arXiv1996

New type of beam size effect and the $W$-boson production at $μ^+μ^-$ colliders

The cross section for the reactions of the type $μ^-μ^+ \to e\barν_e X$ can not be calculated by the standard methods due to the $t$--channel singularity in the physical region. In this letter we show that accounting for the finite sizes of the colliding beams results in the regularization of this singularity. The finite cross section, which is obtained in this way, turns out to be linear proportional to the transverse sizes of the colliding beams. As an application of the above result, we calculate the cross section of the $W$ boson production at $μ^+μ^-$ colliders in the reaction $μ^- μ^+ \to e\barν_e W^+$.

hep-ph↗
arXiv1995

Two-loop $O(N_fα_s^2)$ correction to the decay width of the Higgs boson to two massive fermions

We present an analytical calculation of additional real or virtual radiation of the light fermion pair in the fermionic decay of the Higgs boson $ H \to f_1\bar f_1$ for arbitrary ratios of the Higgs boson mass to the $f_1$ fermion mass. This result gives us a value of the $O(N_f α_s^2)$ radiative correction to the inclusive decay rate $ H \to f_1\bar f_1$. Using this result in the framework of the Brodsky-Mackenzie-Lepage scheme, we discuss the scale setting in the one-loop QCD correction to the decay width $ H \to f_1\bar f_1$ for arbitrary relation between the Higgs boson and fermion masses.

hep-ph↗
arXiv1995

Two -loop $O(G_F{M_H}^2)$ radiative corrections to the Higgs decay width $H \to γγ$ for large Higgs boson masses

This note is devoted to the calculation of the two-loop $O(G_F {M_H}^2)$ radiative corrections to the Higgs decay width $H \to γγ$ for large values of the Higgs boson mass $M_H$ within the Minimal Standard Model. The use of the Equivalence Theorem makes it possible to reduce the problem to the consideration of the physical Higgs boson field and the Goldstone bosons $w^{+},w^{-},z$. We present analytical results for the various two- and three-particle absorptive parts of two-loop contributions, using dispersive techniques, analytic results for all but one of the dispersive contributions. The typical size of the correction is $\sim ~30 $ percent for a Higgs boson mass of order $1~TeV$.

hep-ph↗
arXiv1995

About the modern "experimental value" of W boson width.

It is shown that the methods which have been used up to now to determine the $W$ width from the $p\bar p$ data confirm the SM predictions for some combinations of various phenomenological parameters, however, they do not give an independent value for the $W$ width. Moreover, the accuracy that could be achieved in future experimental checks of SM predictions for such quantities is limited by effects which require detailed theoretical study.

hep-ph↗
arXiv1995

QCD Radiative Correction to Zero Recoil Sum Rules for Heavy Flavor Transitions in the Small Velocity Limit.

We consider the small velocity sum rules for heavy flavour semileptonic transitions that are used to estimate the zero recoil values of semileptonic heavy flavour form factors. We analyze the complete O($α_S$) radiative correction to these sum rules. The corrections are universal and influence all "model-independent" bounds previously derived for semileptonic form factors at zero recoil.

hep-ph↗