arXiv subjects

Alexander S. Sakharov

Publications and source records attributed to Alexander S. Sakharov.

31 records · Page 2Linked to original sources

arXiv2016

Multihadron production dynamics exploring the energy balance in hadronic and nuclear collisions

The multihadron production in nucleus-nucleus collisions and its interrelation with that in (anti)proton-proton interactions are studied by exploring the charged particle mean multiplicity collision-energy and centrality dependencies in the measurements to date. The study is performed in the framework of the recently proposed effective-energy approach which, under the proper scaling of the collision energy, combines the constituent quark picture with Landau relativistic hydrodynamics counting for the centrality-defined effective energy of participants and relating different types of collisions. Within this approach, the multiplicity energy dependence and the pseudorapidity spectra from the most central nuclear collisions are well reproduced. The study of the multiplicity centrality dependence reveals a new scaling between the measured pseudorapidity spectra and the calculations. By means of this scaling, called the energy balanced limiting fragmentation scaling, one reproduces the pseudorapidity spectra for all centralities. The scaling elucidates some differences in the multiplicity and midrapidity density centrality dependence obtained at RHIC and LHC. These findings reveal an inherent similarity in the multiplicity energy dependence from the most central collisions and centrality data. A new regime in heavy-ion collisions to occur at about a TeV energy is indicated, similar to that observed in the earlier studies of the midrapidity densities. Predictions are made for the mean multiplicities to be measured in proton-proton and heavy-ion collisions at the LHC.

hep-ph↗

arXiv2015

Multiparticle production in nuclear collisions using effective-energy approach

The dependencies of charged particle pseudorapidity density and transverse energy pseudorapidity density at midrapidity on the collision energy and on the number of nucleon participants, or centrality, measured in nucleus-nucleus collisions are studied in the energy range spanning a few GeV to a few TeV per nucleon. The study is based on the earlier proposed model, combining the constituent quark picture together with Landau relativistic hydrodynamics and shown to interrelate the measurements from different types of collisions. Within this picture, the dependence on the number of participants in heavy-ion collisions are found to be well described in terms of the effective energy defined as a centrality-dependent fraction of the collision energy. The effective energy approach is shown to reveal a similarity in the energy dependence for the most central and centrality data in the entire available energy range. Predictions are made for the forthcoming higher-energy measurements in heavy-ion collisions at the LHC.

hep-ph↗

arXiv2014

Effective-energy budget in multiparticle production in nuclear collisions

The dependencies of charged particle pseudorapidity density and transverse energy pseudorapidity density at midrapidity on the collision energy and on the number of nucleon participants, or centrality, measured in nucleus-nucleus collisions are studied in the energy range spanning a few GeV to a few TeV per nucleon. The model in which the multiparticle production is driven by the dissipating effective energy of participants is introduced. The model is based on the earlier proposed approach, combining the constituent quark picture together with Landau relativistic hydrodynamics shown to interrelate the measurements from different types of collisions. Within this model, the dependence on the number of participants in heavy-ion collisions are found to be well described in terms of the effective energy defined as a centrality-dependent fraction of the collision energy. For both variables under study, the effective energy approach reveals a similarity in the energy dependence obtained for the most central collisions and centrality data in the entire available energy range. Predictions are made for the investigated dependencies for the forthcoming higher energy measurements in heavy-ion collisions at the LHC.

nucl-th↗

arXiv2012

Prospective Constraints on Neutrino Masses from a Core-Collapse Supernova

We discuss the prospects for improved upper limits on neutrino masses that may be provided by a core-collapse supernova explosion in our galaxy, if it exhibits time variations in the neutrino emissions on the scale of a few milliseconds as suggested by recent two-dimensional simulations. Analyzing simulations of such neutrino emissions using the wavelet technique adopted in [1], we find that an upper limit m_nu ~ 0.14 eV could be established at the 95% confidence level if the time variations in emissions were to be preserved during neutrino propagation to the Earth.

hep-ph↗

arXiv2012

Probing Lorentz Violation in Neutrino Propagation from a Core-Collapse Supernova

Supernova explosions provide the most sensitive probes of neutrino propagation, such as the possibility that neutrino velocities might be affected by the foamy structure of space-time thought to be generated by quantum-gravitational (QG) effects. Recent two-dimensional simulations of the neutrino emissions from core-collapse supernovae suggest that they might exhibit variations in time on the scale of a few milliseconds. We analyze simulations of such neutrino emissions using a wavelet technique, and consider the limits that might be set on a linear or quadratic violation of Lorentz invariance in the group velocities of neutrinos of different energies, v/c = [1 \pm (E/M_{nuLV1})] or [1 \pm (E/M_{\nuLV2})^2], if variations on such short time scales were to be observed, where the mass scales M_{nuLVi} might appear in models of quantum gravity. We find prospective sensitivities to M_{nuLV1} ~ 2 X 10^{13} GeV and M_{nuLV2} ~ 10^6 GeV at the 95% confidence level, up to two orders of magnitude beyond estimates made using previous one-dimensional simulations of core-collapse supernovae. We also analyze the prospective sensitivities to scenarios in which the propagation times of neutrinos of fixed energies are subject to stochastic fluctuations.

hep-ph↗

arXiv2010

Relating multihadron production in hadronic and nuclear collisions

The energy-dependence of charged particle mean multiplicity and pseudorapidity density at midrapidity measured in nucleus-nucleus and (anti)proton-proton collisions are studied in the entire available energy range. The study is performed using a model, which considers the multiparticle production process according to the dissipating energy of the participants and their types, namely a combination of the constituent quark picture together with Landau relativistic hydrodynamics. The model reveals interrelations between the variables under study measured in nucleus-nucleus and nucleon-nucleon collisions. Measurements in nuclear reactions are shown to be well reproduced by the measurements in (anti)proton-proton interactions common and the corresponding fits are presented. Different observations in other types of collisions are discussed in the framework of the proposed model. Predictions are made for measurements at the forthcoming LHC energies.

hep-ph↗

arXiv2006

Probing Brane-World Scenarios with Vacuum Refraction of Light Using Gamma-Ray Bursts

We argue that in fat brane-world scenarios the light propagating in vacuum will, because of massive ``Kaluza-Klein'' (KK) excitations, experience a refraction. The motion of a photon inside a fat brane can be decomposed in the longitudinal and transverse directions with respect to the surface of the brane. Since the light observable propagation is related only with the longitudinal motion, the observed speed of light depends on the value of the momentum transverse fraction contributing as the massive KK excitations. This is directly connected with the energy of the particles emitting the light, and hence with the frequency of the light itself. Using recent results on the arrival times of radiation of different energies from the measurements of gamma-ray bursters with known redshifts, we establish the limit M>620 TeV on the inverse thickness of the brane, and thus on the masses of the KK excitations. This limit exceeds by at least one order of magnitude the typical energy scale currently in use to characterize brane phenomena in the realm of future colliders.

hep-ph↗

arXiv2005

Multihadron production features in different reactions

We consider multihadron production processes in different types of collisions in the framework of the picture based on dissipating energy of participants and their types. In particular, the similarities of such bulk observables like the charged particle mean multiplicity and the pseudorapidity density at midrapidity measured in nucleus-nucleus, (anti)proton-proton and electron-positron interactions are analysed. Within the description proposed a good agreement with the measurements in a wide range of nuclear collision energies from AGS to RHIC is obtained. The predictions up to the LHC energies are made and compared to experimental extrapolations.

hep-ph↗

arXiv2005

Robust Limits on Lorentz Violation from Gamma-Ray Bursts

We constrain the possibility of a non-trivial refractive index in free space corresponding to an energy-dependent velocity of light: c(E) \simeq c_0 (1 - E/M), where M is a mass scale that might represent effect of quantum-gravitational space-time foam, using the arrival times of sharp features observed in the intensities of radiation with different energies from a large sample of gamma-ray bursters (GRBs) with known redshifts. We use wavelet techniques to identify genuine features, which we confirm in simulations with artificial added noise. Using the weighted averages of the time-lags calculated using correlated features in all the GRB light curves, we find a systematic tendency for more energetic photons to arrive earlier. However, there is a very strong correlation between the parameters characterizing an intrinsic time-lag at the source and a distance-dependent propagation effect. Moreover, the significance of the earlier arrival times is less evident for a subsample of more robust spectral structures. Allowing for intrinsic stochastic time-lags in these features, we establish a statistically robust lower limit: M > 0.9x10^{16} GeV on the scale of violation of Lorentz invariance.

astro-ph↗

arXiv2005

On similarities of bulk observables in nuclear and particle collisions

We study the regularities in the multiparticle production data obtained from different types of collisions indicating the universality of the hadroproduction process. The similarities of such bulk variables like the charged particle mean multiplicity and the pseudorapidity density at midrapidity measured in nucleus-nucleus, (anti)proton-proton and e+e- interactions are analysed according to the dissipating energy of participants and their types. This approach shows a good agreement with the measurements in a wide range of nuclear collision energies from AGS to RHIC. The predictions up to the LHC energies are made and compared to experimental extrapolations.

hep-ph↗

arXiv2002

Antimatter regions in the baryon-dominated Universe

Quantum fluctuations of a complex, baryonic charged scalar field caused by inflation can generate large domains, which convert later into antimatter regions. As a result the Universe can become globally matter-dominated, with minor contribution of antimatter regions. The distribution and evolution of such antimatter regions could cause every galaxy to be a harbour of an anti-star globular cluster. At the same time, the scenario does not lead to large-scale isocuvature perturbations, which would disturb observable CMB anisotropy. The existence of one of such antistar globular cluster in our Galaxy does not contradict the observed $γ$-ray background, but the expected fluxes of $\bar{\rm ^4He}$ and $\bar{\rm ^3He}$ from such an antimatter object are definitely accessible to the sensitivity of the coming AMS--02 experiment.

hep-ph↗

arXiv2001

The Formation of Primary Galactic Nuclei during Phase Transitions in the Early Universe

A new mechanism describing the formation of protogalaxies is proposed, which is based on the second- order phase transition in the inflation stage and the domain wall formation upon the end of inflation. The presence of closed domain walls with the size markedly exceeding the cosmological horizon at the instant of their formation and the wall collapse in the postinflation epoch (when the wall size becomes comparable with the cosmological horizon), which leads to the formation of massive black hole clusters that can serve as nuclei for the future galaxies. The black hole mass distributions obtained do not contradict the available experimental data. The number of black holes with M ~ 100 solar masses ($M_{\odot}$) and above is comparable with the number of Galaxies in the visible Universe. Development of the proposed approach gives ground for a principally new scenario of the galaxy formation in the model of hot Universe.

hep-ph↗

arXiv2000

Possible Origin of Antimatter Regions in the Baryon Dominated Universe

We discuss the evolution of U(1) symmetric scalar field at the inflation epoch with a pseudo Nambu-Goldstone tilt revealing after the end of exponential expansion of the Universe. The U(1) symmetry is supposed to be associated with baryon charge. It is shown that quantum fluctuations lead in natural way to baryon dominated Universe with antibaryon excess regions. The range of parameters is calculated at which the fraction of Universe occupied by antimatter and the size of antimatter regions satisfy the observational constraints, survive to the modern time and lead to effects, accessible to experimental search for antimatter.

hep-ph↗