<p>We derive the covariant generalization of the Frank-Tamm formula describing the Cherenkov radiation by a charged particle moving uniformly with a speed faster than the local speed of light within a homogeneous dielectric medium. We use our result to derive the covariant Cherenkov radiation reaction force and obtain a 4-force explicitly orthogonal to particle 4-velocity consistent with a relativistic friction force. We present the photon emission spectrum that is dependent primarily on the dielectric properties of the medium. We hint at a possible use of this work to interpret an excess of soft photons seen in relativistic hadron collisions.</p>

United States

Will Price

Czechia

Martin S. Formanek

Johann Rafelski

Covariant Cherenkov radiation and its friction force

We propose an external field approach to evaluating effective action allowing the interaction to act everywhere at all times (everlasting). Requiring that the asymptotic gauge fields are always interacting, we implement displacement fields encoding polarization corrections into the derivation of effective action. The result is a novel polarization summation for one-cut reducible loop diagrams, which can be applied to two cases: transient quasiconstant electromagnetic fields and everlasting interactions. In the first case, a perturbative expansion of our result recovers the Schwinger-Dyson reducible diagram series with a Landau pole. The everlasting summation evaluated in nonperturbative fashion removes the Landau pole, providing a new avenue for modeling strongly interacting theories.

Germany

Stefan Evans

Everlasting interaction: Polarization summation without a Landau pole

We explore the hypothesis that the abundant presence of relativistic antimatter (positrons) in the primordial Universe is the source of the intergalactic magnetic fields we observe in the Universe today. We evaluate both Landau diamagnetic and magnetic dipole moment paramagnetic properties of the very dense primordial electron-positron <math><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math>-plasma, and obtain in quantitative terms the relatively small magnitude of the <math><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> magnetic moment polarization asymmetry required to produce a consistent self-magnetization in the Universe.

Andrew Steinmetz

Cheng Tao Yang

Matter-antimatter origin of cosmic magnetism

Using the external-field method, i.e., evaluating the effective action <math><msub><mi>V</mi><mi>eff</mi></msub></math> for an arbitrarily strong constant and homogeneous field, we explore nonperturbative properties of QED allowing arbitrary gyromagnetic ratio <math><mi>g</mi></math>. We find a cusp at <math><mi>g</mi><mo>=</mo><mn>2</mn></math> in (a) The QED <math><msub><mi>b</mi><mn>0</mn></msub></math>-renormalization group coefficient, and in the infinite-wavelength limit in (b) a subclass containing the pseudoscalar <math><msup><mi>P</mi><mrow><mn>2</mn><mi>n</mi></mrow></msup><mo>=</mo><mo>(</mo><mover><mi>E</mi><mo>→</mo></mover><mo>·</mo><mover><mi>B</mi><mo>→</mo></mover><msup><mo>)</mo><mrow><mn>2</mn><mi>n</mi></mrow></msup></math> of light-light scattering coefficients. Properties of <math><msub><mi>b</mi><mn>0</mn></msub></math> imply for certain domains of <math><mi>g</mi></math> asymptotic freedom in an Abelian theory.

Lance Labun

Study of QED singular properties for variable gyromagnetic ratio <math><mrow><mi>g</mi><mo>≃</mo><mn>2</mn></mrow></math>

We investigate the electromagnetic response of a viscous quark-gluon plasma in the framework of the relativistic Boltzmann equation with current conserving collision term. Our formalism incorporates dissipative effects at all orders in linear response to the electromagnetic field while accounting for the full space and time dependence of the perturbing fields. As an example, we consider the collision of two nuclei in a stationary, homogeneous quark-gluon plasma. We show that for large collision energies the induced magnetic fields are governed by the response of quark-gluon plasma along the light cone. In this limit, we derive an analytic expression for the magnetic field along the beam axis between the receding nuclei and show that its strength varies only weakly with collision energy for <math><msqrt><msub><mi>s</mi><mi>NN</mi></msub></msqrt><mo>≥</mo><mn>30</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>.

Christopher Grayson

Martin Formanek

Berndt Müller

Dynamic magnetic response of the quark-gluon plasma to electromagnetic fields

We evaluate for the inhomogeneous static electric Sauter step potential the imaginary part of the emerging homogeneous in electric field effective Euler-Heisenberg-Schwinger action sourced by vacuum fluctuations of a charged particle with magnetic moment of arbitrary strength. The result is convergent for all values of gyromagnetic ratio g, periodic in g, with a cusp at <math><mi>g</mi><mo>=</mo><mn>2</mn></math>. We consider the relation to the QED beta-function which is also found to be periodic in g. We confirm presence of asymptotic freedom conditions using this novel method and document a wider range of g-values for which asymptotic freedom is present.

Emergence of periodic in magnetic moment effective QED action

We investigate the strange particle composition of the expanding early Universe in the hadron epoch <math><msub><mrow><mi>T</mi></mrow><mrow><mi>h</mi></mrow></msub><mo>≈</mo><mn>150</mn><mo>≥</mo><mi>T</mi><mo>≥</mo><mn>10</mn></math> MeV. We study strangeness yield in thermal and chemical equilibrium constrained by prescribed conserved entropy per baryon in a charge neutral and strangeness neutral <math><mo>〈</mo><mi>s</mi><mo>−</mo><mover><mrow><mi>s</mi></mrow><mrow><mo>¯</mo></mrow></mover><mo>〉</mo></math> Universe. Turning to kinetic processes in a Hubble expanding Universe, we determine the conditions at which at decreasing temperature T individual strangeness producing reactions fall out of detailed balance between decay and back-reaction strangeness production rates: This is done by comparing the relevant reaction rates to the Hubble expansion rate. We allow for weak, electromagnetic, and strong interaction processes. The weak interaction <math><msup><mrow><mi>μ</mi></mrow><mrow><mo>±</mo></mrow></msup><mo>+</mo><msub><mrow><mi>ν</mi></mrow><mrow><mi>μ</mi></mrow></msub><mo>→</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>±</mo></mrow></msup></math> freezeout is at <math><msubsup><mrow><mi>T</mi></mrow><mrow><mi>f</mi></mrow><mrow><msup><mrow><mi>K</mi></mrow><mrow><mo>±</mo></mrow></msup></mrow></msubsup><mo>=</mo><mn>33.8</mn><mtext> MeV</mtext></math>; the electromagnetic process <math><msup><mrow><mi>l</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>+</mo><msup><mrow><mi>l</mi></mrow><mrow><mo>+</mo></mrow></msup><mo>→</mo><mi>ϕ</mi></math> freezeout is at <math><msubsup><mrow><mi>T</mi></mrow><mrow><mi>f</mi></mrow><mrow><mi>ϕ</mi></mrow></msubsup><mo>=</mo><mn>23</mn><mo>∼</mo><mn>25</mn><mtext> MeV</mtext></math>; and the hadronic reaction <math><mi>π</mi><mo>+</mo><mi>π</mi><mo>→</mo><mi>K</mi></math> freezeout is at <math><msubsup><mrow><mi>T</mi></mrow><mrow><mi>f</mi></mrow><mrow><mi>K</mi></mrow></msubsup><mo>=</mo><mn>19.8</mn><mtext> MeV</mtext></math>.

Cosmological strangeness abundance

We investigate the strong acceleration properties of the radiation reaction force and identify a new and promising limiting acceleration feature in the Eliezer-Ford-O’Connell model; in the strong field regime, for many field configurations, we find an upper limit to acceleration resulting in a bound to the rate of radiation emission. If this model applies, strongly accelerated particles are losing energy at a much slower pace than predicted by the usual radiation reaction benchmark, the Landau-Lifshitz equation, which certainly cannot be used in this regime. We explore examples involving various “constant” electromagnetic field configurations and study particle motion in a light plane wave as well as in a material medium.

Radiation reaction and limiting acceleration

We explore a novel method of describing the radiation friction of particles traveling through a mechanically resistive medium. We introduce a particle motion induced matter warping along the path in a manner assuring that charged particle dynamics occurs subject to radiative energy loss described by the Larmor formula. We compare our description with the Landau-Lifshitz-like model for the radiation friction and show that the established model exhibits nonphysical behavior. Our approach predicts in the presence of large mechanical friction an upper limit on radiative energy loss being equal to the energy loss due to the mechanical medium resistance. We demonstrate that mechanical friction due to strong interactions, for example of quarks in quark-gluon plasma, can induce significant soft photon radiation.

Radiation reaction friction: Resistive material medium

We study the response of the electron mass to an externally applied electrical field. As a consequence of nonlinear electromagnetic (EM) effective action, the mass of a particle diminishes in the presence of an externally applied electric field. We consider modification of the muon anomalous magnetic moment <math><mi>g</mi><mo>−</mo><mn>2</mn></math> due to electron loop insert in higher order. Since the virtual electron pair is in close proximity to the muon, it experiences strong field phenomena. We show that the current theory-experiment muon <math><mi>g</mi><mo>−</mo><mn>2</mn></math> discrepancy could originate in the (virtual) electron mass nonperturbative modification by the strong muon EM field. The magnitude of the electron mass modification can be also assessed via enhancement of <math><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math>-pair production in strong fields.