Mass Frame Research Articles

Momentum Regularity and Stability of the Relativistic Vlasov-Maxwell-Boltzmann System

In the study of solutions to the relativistic Boltzmann equation, their regularity with respect to the momentum variables has been an outstanding question, even local in time, due to the initially unexpected growth in the post-collisional momentum variables which was discovered in 1991 by Glassey & Strauss \cite{MR1105532}. We establish momentum regularity within energy spaces via a new splitting technique and interplay between the Glassey-Strauss frame and the center of mass frame of the relativistic collision operator. In a periodic box, these new momentum regularity estimates lead to a proof of global existence of classical solutions to the two-species relativistic Vlasov-Boltzmann-Maxwell system for charged particles near Maxwellian with hard ball interaction.

Supersymmetry hidden in the continuum

We study models where the superpartners of the ordinary particles have continuous spectra rather than being discrete states, which can occur when the supersymmetric standard model is coupled to an approximately conformal sector. We show that when superpartners that are well into the continuum are produced at a collider, they tend to have long decay chains that step their way down through the continuum emitting many fairly soft standard model particles along the way, with a roughly spherical energy distribution in the center of mass frame.

Acceleration of particles near the inner black hole horizon

We study the possibility of obtaining unbound energy E_{c.m.} in the centre of mass frame when two particles collide near the inner black hole horizon. We consider two different cases - when both particles move (i) in the same direction or (ii) in the opposite ones. We also discuss two different versions of the effect - whether an infinite energy can be released in the collision (strong version) or the energy E_{c.m.} is finite but can be made as large as one likes (weak version). We demonstrate that the strong version of the effect is impossible in both cases (i) and (ii). In case (i) this is due to the fact that in the situation when E_{c.m.} formally diverges on the horizon, one of particles passes through the bifurcation point where two horizons meet while the second particle does not, so collision does not occur. In case (ii), both particles hit different branches of the horizon. The weak version is possible in both cases, provided at least one of particles starts its motion inside the horizon along the direction of spatial symmetry from infinity.

BEC, the $\tau$-Model, and Jets at the Z Pole

Bose-Einstein correlations of pairs of identical charged pions produced in hadronic Z decays are analyzed in terms of various parametrizations. A good description is achieved using a Levy stable distribution in conjunction with a model where a particle's momentum is highly correlated with its space-time point of production, the τ -model. However, a small but significant elongation of the particle emission region is observed in the Longitudinal Center of Mass frame, which is not accommodated in the τ -model. Further, for three-jet events the region is found to be larger in the event plane than out of the plane.

On collisions with unlimited energies in the vicinity of Kerr and Schwarzschild black hole horizons

Two particle collisions close to the horizon of the rotating nonextremal Kerr's and Schwarzschild black holes are analyzed. For the case of multiple collisions it is shown that high energy in the centre of mass frame occurs due to a great relative velocity of two particles and a large Lorentz factor. The dependence of the relative velocity on the distance to horizon is analyzed, the time of movement from the point in the accretion disc to the point of scattering with large energy as well as the time of back movement to the Earth are calculated. It is shown that they have reasonable order.

Quasiclassical Trajectory Calculations for the Reaction Ne + H2+→ NeH++ H

Quasiclassical trajectory (QCT) calculations of Ne + reaction have been carried out on the adiabatic potential energy surface of the ground state A'. The reaction probability of the title reaction for J = 0 has been calculated, and the QCT result is consistent with the previous quantum mechanical wave packet result. Quasiclassical trajectory calculations of the four polarization-dependent differential cross sections have been carried out in the center of mass (CM) frame. The P(), P() and P(, ) distributions, the k-k'-j' correlation and the angular distribution of product rotational vectors are presented in the form of polar plots. Due to the well in A' PES, the reagent vibrational excitation has greater influence on the polarization of the product rotational angular momentum vectors j' than the collision energy.

Boosting the [formula omitted] charge asymmetry

We propose a kinematical enhancement of the tt¯ charge asymmetry at the LHC by selecting events with the tt¯ centre of mass frame highly boosted along the beam axis. This kinematical selection increases the asymmetries and their significance up to a factor of two in a rather model-independent fashion. Hence, it can be a perfect complement to enhance model discrimination at the LHC.

Back-to-back pair correlation of Majorana neutrinos with transit magnetic moments

The pair production of Majorana neutrinos with transit magnetic moments from the annihilation of charged particles in colliding experiments is discussed using the Pauli interaction, through which the neutral neutrinos with magnetic moments can be probed by the photon. The pair of neutrinos with different flavors are produced due to the transit magnetic moment coupling. We discuss the correlations of flavors in pairs produced back-to-back in the center of the mass frame, where the angular distribution peaks at $\ensuremath{\theta}=\ensuremath{\pi}/2$ with respect to the beam direction. We demonstrate that the flavor mixing angle can be inferred by measuring the flavor correlation in pairs.

Static and spherically symmetric black holes inf(R)theories

We study some features of static and spherically symmetric solutions (SSS) with a horizon in $f(R)$ theories of gravitation by means of a near-horizon analysis. A necessary condition for an $f(R)$ theory to have this type of solution is obtained. General features of the effective potential are deduced, and it is shown that there exists a limit on the curvature at the horizon, in both cases for any $f(R$). Finally, we calculate the expression for the energy of the collision of two masive particles in the center of mass frame.

BLACK HOLE AS A SUPERCOLLIDER

Recently, it was found that in the vicinity of the black hole horizon of a rotating black hole two particles can collide in such a way that the energy in their centre of mass frame becomes infinite (so-called BSW effect). I give a brief review of basic features of this effect and show that this is a generic property of rotating black holes. In addition, there exists its counterpart for radial motion of charged particles in the charged black hole background. Simple kinematic explanation is suggested that is based on observation that all massive particles fall in two classes. In the first case (by definition, "usual particles"), the velocity approaches that of light on the horizon in the locally-nonrotating frame due to special relationship between the energy and the angular momentum. In the second case, it tends to some value less than speed of light. As a result, the relative velocity also tends to the speed of light with infinitely growing Lorentz factor.

General stationary charged black holes as charged particle accelerators

We study the possibility of getting infinite energy in the center of mass frame of colliding charged particles in a general stationary charged black hole. For black holes with two-fold degenerate horizon, it is found that arbitrary high center-of-mass energy can be attained, provided that one of the particle has critical angular momentum or critical charge, and the remained parameters of particles and black holes satisfy certain restriction. For black holes with multiple-fold degenerate event horizons, the restriction is released. For non-degenerate black holes, the ultra-high center-of-mass is possible to be reached by invoking the multiple scattering mechanism. We obtain a condition for the existence of innermost stable circular orbit with critical angular momentum or charge on any-fold degenerate horizons, which is essential to get ultra-high center-of-mass energy without fine-tuning problem. We also discuss the proper time spending by the particle to reach the horizon and the duality between frame dragging effect and electromagnetic interaction. Some of these general results are applied to braneworld small black holes.

Polarized and unpolarized Drell-Yan angular distribution in the helicity formalism

We present a decomposition of the hadronic tensor for a general polarized Drell-Yan process AB --> l^+ l^- X in terms of helicity structure functions using the helicity axes of the dilepton rest frame as a basis. Next, we consider a QCD parton model and in the framework of a generalized QCD factorization scheme, which applies when the dilepton invariant mass M is much larger than the transverse component of the photon momentum, q_T, in the hadronic center of mass frame. In this approximation we compute the angular distribution of the unpolarized Drell Yan cross section and of the Sivers effect, in single polarized Drell-Yan scattering, by taking into account the transverse motion of partons inside the initial hadrons, k_\perp. Interesting and simple results are found in the kinematical region of k_\perp similar to q_T << M, to first order in a q_T / M expansion. Finally, explicit analytical expressions, convenient for phenomenological studies, are obtained assuming a factorized Gaussian dependence on intrinsic momenta for the unpolarized and Sivers distribution functions, in analogy to those obtained for semi-inclusive deep inelastic scattering.

Quasi-classical trajectory studies of the stereodynamics of the reaction O + HCl → ClO + H

The stereodynamics of the O + HCl → ClO + H reaction are investigated by quasi-classical trajectory (QCT) method. The calculations are carried out on the ground 1 1A′ potential energy surface (PES). The orientation and alignments of the product rotational angular momentum for the title reaction are reported. The influence of collision energy on the product vector properties is also studied in the present work. Four (2π/σ)(dσ00/dωt), (2π/σ)(dσ20/dωt), (2π/σ)(dσ22+/dωt), and (2π / σ)(dσ21−/dωt), and have been calculated in the center of mass frame.

Acceleration of particles by black holes: Kinematic explanation

A new simple and general explanation of the effect of acceleration of particles by black holes to infinite energies in the centre of mass frame is suggested. It is based on kinematics of particles moving near the horizon. This effect arises when particles of two kinds collide near the horizon. For massive particles, the first kind represents a particle with the generic energy and angular momentum (I call them "usual"). Near the horizon, such a particle has a velocity almost equal to that of light in the frame that corotates with a black hole (the frame is static if a black hole is static). The second kind (called "critical") consists of particles with the velocity v<c near the horizon due to special relationship between the energy and angular momentum (or charge). As a result, the relative velocity approaches the speed of light c, the Lorentz factor grows unbound. This explanation applies both to generic rotating black holes and charged ones (even for radial motion of particles). If one of colliding particles is massless (photon), the critical particle is distinguished by the fact that its frequency is finite near the horizon. The existence (or absence) of the effect is determined depending on competition of two factors - gravitational blue shift for a photon propagating towards a black hole and the Doppler effect due to transformation from the locally nonrotating frame to a comoving one. Classification of all possible types of collisions is suggested depending on whether massive or massless particle is critical or usual.

Membrane-type metamaterials: Transmission loss of multi-celled arrays

Acoustic metamaterials with negative dynamic mass density have been shown to demonstrate a five-fold increase in transmission loss (TL) over mass law predictions for a narrowband (100 Hz) at low frequencies (100–1000 Hz). The present work focuses on the scale-up of this effect by examining the behavior of multiple elements arranged in arrays. Single membranes were stretched over rigid frame supports and masses were attached to the center of each divided cell. The TL behavior was measured for multiple configurations with different magnitudes of mass distributed across each of the cell membranes in the array resulting in a multipeak TL profile. To better understand scale-up issues, the effect of the frame structure compliance was evaluated, and more compliant frames resulted in a reduction in the TL peak frequency bandwidth. In addition, displacement measurements of frames and membranes were performed using a laser vibrometer. Finally, the measured TL of the multi-celled structure was compared with the TL behavior predicted by finite element analysis to understand the role of nonuniform mass distribution and frame compliance.

Entropy scaling in high-energy nucleus–nucleus interactions

We studied the multiparticle production in high-energy nucleus–nucleus interactions in terms of particle entropy in 16O–AgBr and 32S–AgBr interactions at 60 A GeV and 200 A GeV, respectively. An approximate scaling behavior of total produced entropy normalized to maximum rapidity in the center of mass frame measured in different rapidity bins has been reported. The scaling behavior is not supported either by the FRITIOF model or by the Monte Carlo simulated events.

Determination of sputtered atom densities and velocities via simulation

Transport of sputtered atoms in a plasma sputtering unit is simulated using two known elastic collision models. The methods of studying the collision of two atoms are isotropic random scattering angle in the center of mass frame and the so-called center to center collision model in which the impact parameter is ignored and the two particles collide such as two material points. The obtained results for the density and velocity of sputtered atoms in both models are compared with some experimental reports. This investigation shows that the copper and argon atoms present pointlike behavior in the collision process.

EXPERIMENTAL INVESTIGATION OF 6Be CLUSTER DECAY

A complete kinematics measurement was performed using the 6 Li (3 He ,t) charge exchange reaction to populate 6 Be at Elab = 50 MeV . Decay mode of the ground and first excited states were studied through the analysis of the energy and angular distributions of the break-up particles in the 6 Be center of mass frame. Two-body decay is observed above the first excited state but not firmly assigned to a 6 Be resonant state. Experimental challenges regarding the identification of true 6 Be events in the excitation energy region 5 &lt; Ex &lt; 20 MeV are discussed.

Acceleration of colliding shells around a black hole: Validity of the test particle approximation in the Banados-Silk-West process

Recently, Banados, Silk and West (BSW) showed that the total energy of two colliding test particles has no upper limit in their center of mass frame in the neighborhood of an extreme Kerr black hole, even if these particles were at rest at infinity in the infinite past. We call this mechanism the BSW mechanism or BSW process. The large energy of such particles would generate strong gravity, although this has not been taken into account in the BSW analysis. A similar mechanism is seen in the collision of two spherical test shells in the neighborhood of an extreme Reissner-Nordstr\"om black hole. In this paper, in order to draw some implications concerning the effects of gravity generated by colliding particles in the BSW process, we study a collision of two spherical dust shells, since their gravity can be exactly treated. We show that the energy of two colliding shells in the center of mass frame observable from infinity has an upper limit due to their own gravity. Our result suggests that an upper limit also exists for the total energy of colliding particles in the center of mass frame in the observable domain in the BSW process due the gravity of the particles.

THEORETICAL STUDY OF THE STEREO-DYNAMICS OF THE REACTION O + HCl → ClO + H

Quasi-classical trajectory (QCT) method is used to study the stereo-dynamics of the title reaction on the ground 1 1A′ potential energy surface (PES). Differential cross-sections (DCSs) and alignments of the product rotational angular momentum for the reaction are reported. The influence of collision energy on the product vector properties is also studied in the present work. The distribution of angle between k and j′, P(θr), the distribution of dihedral angle denoting k-k′-j′ correlation, P(ϕr) ⋅ (2π/σ)( d σ00/ d ωt), (2π/σ)( d σ20/ d ωt), (2π/σ)( d σ22+/ d ωt) and (2π/σ)(dσ21-/dωt) have been calculated in the center of mass frame, respectively.