5954843
Dynamical renormalization group approach to quantum kinetics in scalar and gauge theories
We derive quantum kinetic equations from a quantum field theory implementing a diagrammatic perturbative expansion improved by a resummation via the dynamical renormalization group. The method begins by obtaining the equation of motion of the distribution function in perturbation theory. The solution of this equation of motion reveals secular terms that grow in time, the dynamical renormalization group resums these secular terms in real time and leads directly to the quantum kinetic equation. This method allows to include consistently medium effects via resummations akin to hard thermal loops but away from equilibrium. A close relationship between this approach and the renormalization group in Euclidean field theory is established. In particular, coarse graining, stationary solutions, relaxation time approximation and relaxation rates have a natural parallel as irrelevant operators, fixed points, linearization and stability exponents in the Euclidean renormalization group, respectively. We used this method to study the relaxation in a cool gas of pions and sigma mesons in the O(4) chiral linear sigma model. We obtain in relaxation time approximation the pion and sigma meson relaxation rates. We also find that in large momentum limit emission and absorption of massless pions result in threshold infrared divergence in sigma meson relaxation rate and lead to a crossover behavior in relaxation. We then study the relaxation of charged quasiparticles in scalar electrodynamics (SQED). We begin with a gauge invariant description of the distribution function and implement the hard thermal loop resummation for longitudinal and transverse photons as well as for the scalars. While longitudinal, Debye screened photons lead to purely exponential relaxation, transverse photons, only dynamically screened by Landau damping lead to anomalous (non-exponential) relaxation, thus leading to a crossover between two different relaxational regimes. We emphasize that infrared divergent damping rates are indicative of non-exponential relaxation and the dynamical renormalization group reveals the correct relaxation directly in real time. Furthermore the relaxational time scales for charged quasiparticles are similar to those found in QCD in a self-consistent HTL resummation. Finally we also show that this method provides a natural framework to interpret and resolve the issue of pinch singularities out of equilibrium and establish a direct correspondence between pinch singularities and secular terms in time-dependent perturbation theory. We argue that this method is particularly well suited to study quantum kinetics and transport in gauge theories.
17740001
Nonequilibrium relaxation of Bose-Einstein condensates: Real-time equations of motion and Ward identities
Abstract We present a field-theoretical method to obtain consistently the equations of motion for small amplitude condensate perturbations in a homogeneous Bose-condensed gas directly in real time. It is based on a linear response and combines the Schwinger–Keldysh formulation of nonequilibrium quantum field theory with the Nambu–Gor'kov formalism of quasiparticle excitations in the condensed phase and the tadpole method in quantum field theory. This method leads to causal equations of motion that allow us to study the nonequilibrium evolution as an initial value problem. It also allows us to extract directly the Ward identities, which are a consequence of the underlying gauge symmetry and which in equilibrium lead to the Hugenholtz–Pines theorem. An explicit one-loop calculation of the equations of motion beyond the Hartree–Fock–Bogoliubov approximation reveals that the nonlocal, absorptive contributions to the self-energies corresponding to the Beliaev and Landau damping processes are necessary to fulfill the Ward identities in or out of equilibrium. It is argued that a consistent implementation at low temperatures must be based on the loop expansion, which is shown to fulfill the Ward identities order by order in perturbation theory.
28322811
Dynamical electron mass in a strong magnetic field
Motivated by recent interest in understanding properties of strongly magnetized matter, we study the dynamical electron mass generated through approximate chiral symmetry breaking in QED in a strong magnetic field. We reliably calculate the dynamical electron mass by numerically solving the nonperturbative Schwinger-Dyson equations in a consistent truncation within the lowest Landau level approximation. It is shown that the generation of dynamical electron mass in a strong magnetic field is significantly enhanced by the perturbative electron mass that explicitly breaks chiral symmetry in the absence of a magnetic field.
5549498
PROGRESS ON CHIRAL SYMMETRY BREAKING IN A STRONG MAGNETIC FIELD
The problem of chiral symmetry breaking in QED in a strong magnetic field is briefly reviewed. Recent progress on issues regarding the gauge fixing independence of the dynamically generated fermion mass is discussed.
119494487
REAL-TIME NONEQUILIBRIUM DYNAMICS IN HOT QED PLASMAS
The quantum kinetics of photons in hot QED plasmas is studied directly in real time by implementing the dynamical renormalization group. In contrast to conventional approach, the dynamical renormalization group method consistently includes off-shell (energy non-conserving) effects and accounts for time-dependent collisional kernel. To lowest order we find that in the relaxation time approximation the semihard photon distribution function relaxes with a power law.
35173511
Real time nonequilibrium dynamics in hot QED plasmas: Dynamical renormalization group approach
We study the real-time nonequilibrium dynamics in hot QED plasmas implementing a dynamical renormalization group and using the hard thermal loop (HTL) approximation. The focus is on the study of the relaxation of gauge and fermionic mean fields and on the quantum kinetics of the photon and fermion distribution functions. For semihard photons of momentum eT q \gamma and \bar{q} -> \bar{q}\gamma) at O(\alpha) grows logarithmically in time and is comparable to that produced from on-shell Compton scattering and pair annihilation at O(\alpha \alpha_s). Fermion mean fields relax as e^{-\alpha T t ln(\omega_P t)} with \omega_P=eT/3 the plasma frequency, as a consequence of the emission and absorption of soft magnetic photons. A quantum kinetic equation for hard fermions is obtained directly in real time from a field theoretical approach improved by the dynamical renormalization group. The collision kernel is time-dependent and infrared finite.
109931583
The experimental study on beam-photoelectron instability in BEPC
A vertical coupled bunch instability explained as the photoelectron instability (PEI) was observed in the photon factory at KEK. To further investigate the instability, the experiments on the PEI have been carried out in Beijing Electron Positron Collider (BEPC) with the collaboration between MEP, China and KEK, Japan. Many interesting phenomena have been observed for different sets of parameters.
209835699
Search for anomalous production of events with two photons and additional energetic objects at CDF
We present results of a search for anomalous production of two photons together with an electron, muon, τ lepton, missing transverse energy, or jets using pp collision data from 1.1–2.0  fb-1 of integrated luminosity collected by the Collider Detector at Fermilab (CDF). The event yields and kinematic distributions are examined for signs of new physics without favoring a specific model of new physics. The results are consistent with the standard model expectations. The search employs several new analysis techniques that significantly reduce instrumental backgrounds in channels with an electron and missing transverse energy.
119275511
Gravitational Field Equations and Theory of Dark Matter and Dark Energy
The main objective of this article is to derive new gravitational field equations and to establish a unified theory for dark energy and dark matter. The gravitational field equations with a scalar potential $\varphi$ function are derived using the Einstein-Hilbert functional, and the scalar potential $\varphi$ is a natural outcome of the divergence-free constraint of the variational elements. 
Gravitation is now described by the Riemannian metric 
$g_{\mu\nu}$, the scalar potential $\varphi$ and their interactions, unified by the new field equations. 
From quantum field theoretic point of view, the vector field $\Phi_\mu=D_\mu \varphi$, the gradient of the scalar function $\varphi$, is a spin-1 massless bosonic particle field. The field equations induce a natural duality between the graviton (spin-2 massless bosonic particle) and this spin-1 massless bosonic particle. Both particles can be considered as gravitational force carriers, and as they are massless, the induced forces are long-range forces. The (nonlinear) interaction between these bosonic particle fields leads to a unified theory for dark energy and dark matter. Also, associated with the scalar potential $\varphi$ is the scalar potential energy density $\frac{c^4}{8\pi G} \Phi=\frac{c^4}{8\pi G} g^{\mu\nu}D_\mu D_\nu \varphi$, which represents a new type of energy caused by the non-uniform distribution of matter in the universe. 
The negative part of this potential energy density produces attraction, and the positive part produces repelling force. This potential energy density is conserved with mean zero: $\int_M \Phi dM=0$. 
The sum of this potential energy density 
$\frac{c^4}{8\pi G} \Phi$ and the coupling energy 
 between the energy-momentum tensor $T_{\mu\nu}$ and the scalar potential field $\varphi$ gives rise to a unified theory for dark matter and dark energy: 
The negative part of 
this sum represents the dark matter, which produces attraction, 
and the positive part represents the dark energy, which drives the acceleration of expanding galaxies. 
In addition, the scalar curvature of space-time obeys $R=\frac{8\pi G}{c^4} T + \Phi$. 
Furthermore, the proposed field equations resolve a few difficulties encountered by the classical Einstein field equations.
17747494
Observation of the production of a W boson in association with a single charm quark.
The first observation of the production of a W boson with a single charm quark (c) jet in pp[over ¯] collisions at √s=1.96  TeV is reported. The analysis uses data corresponding to 4.3  fb(-1), recorded with the CDF II detector at the Fermilab Tevatron. Charm quark candidates are selected through the identification of an electron or muon from charm-hadron semileptonic decay within a hadronic jet, and a Wc signal is observed with a significance of 5.7 standard deviations. The production cross section σ(Wc)(p(Tc)>20  GeV/c,|η(c)|<1.5)×B(W→ℓν) is measured to be 13.6(-3.1)(+3.4)  pb and is in agreement with theoretical expectations. From this result the magnitude of the quark-mixing matrix element V(cs) is derived, |V(cs)|=1.08±0.16 along with a lower limit of |V(cs)|>0.71 at the 95% confidence level, assuming that the Wc production through c to s quark coupling is dominant.
33054147
The underlying event in hard interactions at the Tevatron $\bar p p$ collider
For comparison of inclusive jet cross sections measured at hadron-hadron colliders to next-to-leading order (NLO) parton-level calculations, the energy deposited in the jet cone by spectator parton interactions must first be subtracted. The assumption made at the Tevatron is that the spectator parton interaction energy is similar to the ambient level measured in minimum bias events. In this paper, we test this assumption by measuring the ambient charged track momentum in events containing large transverse energy jets at {radical}(s)=1800 GeV and {radical}(s)=630 GeV and comparing this ambient momentum with that observed both in minimum bias events and with that predicted by two Monte Carlo models. Two cones in {eta}-{phi} space are defined, at the same pseudorapidity, {eta}, as the jet with the highest transverse energy (E{sub T}{sup (1)}), and at {+-}90{sup o} in the azimuthal direction, {phi}. The total charged track momentum inside each of the two cones is measured. The minimum momentum in the two cones is almost independent of E{sub T}{sup (1)} and is similar to the momentum observed in minimum bias events, whereas the maximum momentum increases roughly linearly with the jet E{sub T}{sup (1)} over most of the measured range. This study was carried out usingmore » data from the CDF detector taken during Run 1 (1994-1995). The study will help improve the precision of comparisons of jet cross section data and NLO perturbative QCD predictions. The distribution of the sum of the track momenta in the two cones is also examined for five different E{sub T}{sup (1)} bins. The HERWIG and PYTHIA Monte Carlo generators are reasonably successful in describing the data, but neither can describe completely all of the event properties.« less