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Z. K. Silagadze

Publications and source records attributed to Z. K. Silagadze.

At least 73 records · Page 4Linked to original sources

Invariance of the Noether charge

Surprisingly, an interesting property of the Noether charge that it is by itself invariant under the corresponding symmetry transformation is never discussed in quantum field theory or classical mechanics textbooks we have checked. This property is also almost never mentioned in articles devoted to Noether's theorem. Nevertheless, to prove this property in the context of Lagrangian formalism is not quite trivial and the proof, outlined in this article, can constitute an useful and interesting exercise for students.

physics.class-ph↗

Expanding space, quasars and St. Augustine's fireworks

An attempt is made to explain time non-dilation allegedly observed in quasar light curves. The explanation is based on the assumption that quasar black holes are, in some sense, foreign for our Friedmann-Robertson-Walker universe and do not participate in the Hubble flow. Although at first sight such a weird explanation requires unreasonably fine-tuned Big Bang initial conditions, we find a natural justification for it using the Milne cosmological model as an inspiration.

gr-qc↗

Sums of generalized harmonic series for kids from five to fifteen

We examine the remarkable connection, first discovered by Beukers, Kolk and Calabi, between $ζ(2n)$, the value of the Riemann zeta-function at an even positive integer, and the volume of some $2n$-dimensional polytope. It can be shown that this volume is equal to the trace of a compact self-adjoint operator. We provide an explicit expression for the kernel of this operator in terms of Euler polynomials. This explicit expression makes it easy to calculate the volume of the polytope and hence $ζ(2n)$. In the case of odd positive integers, the expression for the kernel enables us to rediscover an integral representation for $ζ(2n+1)$, obtained by a different method by Cvijović and Klinowski. Finally, we indicate that the origin of the miraculous Beukers-Kolk-Calabi change of variables in the multidimensional integral, which is at the heart of this circle of ideas, can be traced to the amoeba associated with the certain Laurent polynomial. The paper is dedicated to the memory of Vladimir Arnold (1937-2010).

math.CA↗

Measurement of the $K_L$ nuclear interaction length in the NaI(Tl) calorimeter

In the study of the reaction $e^+e^-\to K_{S}K_{L}$ at the VEPP-2M $e^+e^-$ collider with the SND detector the nuclear interaction length of $K_{L}$ meson in NaI(Tl) has been measured. Its value is found to be 30--50 cm in the $K_{L}$ momentum range 0.11--0.48 GeV/$c$. The results are compared with the values used in the simulation programs GEANT4 and UNIMOD.

hep-ex↗

Gauge invariant formulation of 3$γ$ decay of particle-antiparticle bound states

We construct the gauge invariant three-photon decay amplitude of particle-antiparticle bound states modeled by the Dyson-Schwinger and Bethe-Salpeter equations. Application to the quark-antiquark ($q\bar{q}$) bound states is emphasized. An essential aspect of our formulation is that it applies to any underlying quantum field theoretic model of the $q\bar{q}$ system, and not just to models, like exact QCD, where the quark self-energy $Σ$ couples to the electromagnetic field solely via dressed quark propagators. In this way, applications to effective field theories and other QCD motivated models are envisioned. The three-photon decay amplitude is constructed by attaching currents to all possible places in the Feynman diagrams contributing to the dressed quark propagator. The gauge invariance of our construction is thus a direct consequence of respecting the underlying structure of the quantum field theory determining the dynamics. In the resultant expression for the three-photon decay amplitude, all the basic ingredients consisting of the bound state wave function, the final-state interaction $q\bar{q}$ $t$ matrix, the dressed quark propagator, and dressed quark currents, are determined by a universal Bethe-Salpeter kernel.

hep-ph↗

On a search for the $η\rightarrow e^+ e^-$ decay at the VEPP-2000 $e^+e^-$ collider

A sensitivity of the VEPP-2000 $e^+e^-$ collider in a search for the rare decay $η\rightarrow e^+ e^-$ has been studied. The inverse reaction $e^+ e^- \rightarrow η$ is proposed for this search. We have analyzed a data sample with an integrated luminosity of 108 nb$^{-1}$ collected with the SND detector in the center-of-mass energy range 520-580 MeV and found no background events for the reaction $e^+ e^- \rightarrow η$ in the decay mode $η\toπ^0π^0π^0$. In the absence of background, a sensitivity to ${\cal B}(η\rightarrow e^+ e^-)$ of $10^{-6}$ can be reached during two weeks of VEPP-2000 operation. Such a sensitivity is better than the current upper limit on ${\cal B}(η\rightarrow e^+ e^-)$ by a factor of 2.3.

hep-ex↗

Search for the $η^{\prime}\to e^+e^-$ decay with the SND detector

A search for the process $e^+e^- \to η^\prime$ has been performed with the SND detector at the VEPP-2000 $e^+e^-$ collider. The data were accumulated at the center-of-mass energy of $957.78\pm 0.06$ MeV with an integrated luminosity of about 2.9 pb$^{-1}$. For reconstruction of the $η^\prime$ meson five decay chains have been used: $η^{\prime}\toηπ^+π^-$ followed by the $η$ decays to $γγ$ and $3π^0 $, and $η^{\prime} \to ηπ^0π^0$ followed by the $η$ decays to $π^+π^-π^0$, $γγ$, and $3π^0$. As a result, the upper limit has been set on the $η^\prime$ electronic width: $Γ_{η^{\prime}\to e^+e^-} < 0.0020$ eV at the 90\% confidence level.

hep-ex↗

Measurement of the $e^+e^- \to ηπ^+π^-$ cross section in the center-of-mass energy range 1.22--2.00 GeV with the SND detector at the VEPP-2000 collider

In the experiment with the SND detector at the VEPP-2000 $e^+e^-$ collider the cross section for the process $e^+e^-\toηπ^+π^-$ has been measured in the center-of-mass energy range from 1.22 to 2.00 GeV. Obtained results are in agreement with previous measurements and have better accuracy. The energy dependence of the $e^+e^-\toηπ^+π^-$ cross section has been fitted with the vector-meson dominance model. From this fit the product of the branching fractions $B(ρ(1450)\toηπ^+π^-)B(ρ(1450)\to e^+e^-)$ has been extracted and compared with the same products for $ρ(1450)\toωπ^0$ and $ρ(1450)\toπ^+π^-$ decays. The obtained cross section data have been also used to test the conservation of vector current hypothesis.

hep-ex↗

arXiv in the classical Russian literature

The creation of arXiv, a highly democratic open access repository of research papers in high-energy physics more than twenty years ago was undoubtedly the most spectacular and landmark event for the high-energy physics community. However, we report a curious observation which indicates that the general cultural significance of this event extends far beyond the boundaries assumed at the beginning.

physics.pop-ph↗

Relativistic mass and modern physics

At first sight, arguments for and against the notion of relativistic mass look like a notorious intra-Lilliputian quarrel between Big-Endians (those who broke their eggs at the larger end) and Little-Endians. However, upon closer inspection we discover that the relativistic mass notion is alien to the spirit of modern physics to a much greater extent than it seems. To demonstrate an abyss between the modern approach and archaic notions, in this paper we explore how the concept of mass is introduced in modern physics. This modern approach reveals a deep cohomological origin of mass.

physics.class-ph↗

Gauge transformations are canonical transformations, redux

In this short note we return to the old paper by Tai L. Chow (Eur. J. Phys. 18 (1997), 467-468) and correct its erroneous final part. We also note that the main result of that paper, that gauge transformations of mechanics are canonical transformations, was known much earlier.

physics.class-ph↗

Study of the process $e^+e^-\toηγ$ in the center-of-mass energy range 1.07--2.00 GeV

The $e^+e^-\toηγ$ cross section has been measured in the center-of-mass energy range 1.07--2.00 GeV using the decay mode $η\to 3π^0$, $π^0\to γγ$. The analysis is based on 36 pb$^{-1}$ of integrated luminosity collected with the SND detector at the VEPP-2000 $e^+e^-$ collider. The measured cross section of about 35 pb at 1.5 GeV is explained by decays of the $ρ(1450)$ and $ϕ(1680)$ resonances.

hep-ex↗

Thin disk of co-rotating dwarfs: a fingerprint of dissipative (mirror) dark matter?

Recent observations indicate that about half of the dwarf satellite galaxies around M31 orbit in a thin plane approximately aligned with the Milky Way. It has been argued that this observation along with several other features can be explained if these dwarf satellite galaxies originated as tidal dwarf galaxies formed during an ancient merger event. However if dark matter is collisionless then tidal dwarf galaxies should be free of dark matter - a condition that is difficult to reconcile with observations indicating that dwarf satellite galaxies are dark matter dominated. We argue that dissipative dark matter candidates, such as mirror dark matter, offer a simple solution to this puzzle.

astro-ph.GA↗

Study of e+e- --> omega pi0 --> pi0 pi0 gamma in the energy range 1.05--2.00 GeV with SND

The cross section for the process e+e- --> omega pi0 --> pi0 pi0 gamma has been measured in the energy range 1.05--2.00 GeV. The experiment has been performed at the e+e- collider VEPP-2000 with the SND detector. The measured e+e- --> omega pi0 cross section above 1.4 GeV is the most accurate to date. Below 1.4 GeV our data are in good agreement with the previous SND and CMD-2 measurements. Data on the e+e- --> omega pi0 cross section are well described by the VMD model with two excited rho-like states. From the measured cross section we have extracted the gamma^* --> omega pi0 transition form factor. It has been found that the VDM model cannot describe simultaneously our data and data obtained from the omega --> pi0 mu+ mu- decay. We have also tested CVC hypothesis comparing our results on the e+e- --> omega pi0 cross section with data on the tau- --> omega pi- nu_{tau} decay.

hep-ex↗

Love story under the H-bomb shadow

The physics is created by human beings with all weaknesses of human nature. This story caught our attention since it demonstrates how fragile the human destiny is and even genius cannot find freedom and preserve human dignity in the face of the totalitarian state.

physics.soc-ph↗

Breaking the light speed barrier

As it is well known, classical special relativity allows the existence of three different kinds of particles: bradyons, luxons and tachyons. Bradyons have non-zero mass and hence always travel slower than light. Luxons are particles with zero mass, like the photon, and they always travel with invariant velocity. Tachyons are hypothetical superluminal particles that always move faster than light. The existence of bradyons and luxons is firmly established, while the tachyons were never reliably observed. In quantum field theory, the appearance of tachyonic degrees of freedom indicates vacuum instability rather than a real existence of the faster-than-light particles. However, recent controversial claims of the OPERA experiment about superluminal neutrinos triggered a renewed interest in superluminal particles. Driven by a striking analogy of the old Frenkel-Kontorova model of a dislocation dynamics to the theory of relativity, we conjecture in this note a remarkable possibility of existence of the fourth type of particles, elvisebrions, which can be superluminal. The characteristic feature of elvisebrions, distinguishing them from tachyons, is that they are outside the realm of special relativity and their energy remains finite (or may even turn to zero) when the elvisebrion velocity approaches the light velocity.

hep-ph↗

Comment on the sums $S(n)=\sum\limits_{k=-\infty}^\infty \frac{1}{(4k+1)^n}$

This is a comment on the papers N. D. Elkies, Amer. Math. Monthly 110 (2003), 561-573 and Cvijovic and J. Klinowski, J. Comput. Appl. Math. 142 (2002), 435-439. We provide an explicit expression for the kernel of the integral operator introduced in the first paper. This explicit expression considerably simplifies the calculation of S(n) and enables a simple derivation of Cvijovic and Klinowski's integral representation for $ζ(2n+1)$.

math.CA↗