119117966
Is there a maximum magnetic field in QED
Abstract It was recently conjectured by Shabad and Usov that there exists in QED a maximum magnetic field of 10 42 G , above which the magnetized vacuum becomes unstable. Using a nonperturbative analysis that consistently incorporates the effective electron mass and the screening effect in a strong magnetic field, we show that the conjectured phenomenon of positronium collapse never takes place. Thus, there does not exist a maximum magnetic field in QED and the magnetized vacuum is stable for all values of the magnetic field.
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.
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.
119072239
Rapid Changes of Photospheric Magnetic Field after Tether-cutting Reconnection and Magnetic Implosion
The rapid, irreversible change of the photospheric magnetic field has been recognized as an important element of the solar flare process. This Letter reports such a rapid change of magnetic fields during the 2011 February 13 M6.6 flare in NOAA AR 11158 that we found from the vector magnetograms of the Helioseismic and Magnetic Imager (HMI) with 12 minute cadence. High-resolution magnetograms of Hinode that are available at ~–5.5, –1.5, 1.5, and 4 hr relative to the flare maximum are used to reconstruct a three-dimensional coronal magnetic field under the nonlinear force-free field (NLFFF) assumption. UV and hard X-ray images are also used to illuminate the magnetic field evolution and energy release. The rapid change is mainly detected by HMI in a compact region lying in the center of the magnetic sigmoid, where the mean horizontal field strength exhibited a significant increase of 28%. The region lies between the initial strong UV and hard X-ray sources in the chromosphere, which are cospatial with the central feet of the sigmoid according to the NLFFF model. The NLFFF model further shows that strong coronal currents are concentrated immediately above the region, and that, more intriguingly, the coronal current system underwent an apparent downward collapse after the sigmoid eruption. These results are discussed in favor of both the tether-cutting reconnection producing the flare and the ensuing implosion of the coronal field resulting from the energy release.
122255934
PROTON BRANCH OF MODIFIED URCA PROCESS IN STRONG MAGNETIC FIELD AND SUPERFLUIDITY OF NEUTRON STAR CORES
The modified URCA process produces efficient neutrino energy losses in neutron star cores, and has been shown to go via neutron and proton branches. Based on the improved electron chemical potential and critical temperature of superfluidity, the effects of strong magnetic field and superfluidity on the proton branch of modified URCA process are investigated simultaneously in this paper. The results show that strong magnetic field enhances the neutrino emissivities compared to the case in zero magnetic field, and superfluidity reduces the emissivities significantly. For the total neutrino emissivities, the magnetic field is dominant at the initial stage of neutron star cooling, but the superfluidity becomes crucial as the temperature drops below the critical temperature.
202105722
Search for strong gravity signatures in same-sign dimuon final states using the ATLAS detector at the LHC
A search for microscopic black holes has been performed in a same-sign dimuon final state using 1.3 fb(-1) of proton-proton collision data collected with the ATLAS detector at a centre of mass energy of 7 TeV at the CERN Large Hadron Collider. The data are found to be consistent with the expectation from the Standard Model and the results are used to derive exclusion contours in the context of a low scale gravity model.
216654949
Searches for low mass Higgs boson at the Tevatron
The last particle predicted by the standard model (SM), which has not yet been observed in experiments, is the Higgs boson. In the SM, the electroweak gauge symmetry is broken through the Higgs mechanism, which postulates the existence of a Higgs field that permeates the entire universe. The SM particles acquire their masses by interacting with the Higgs fields through the exchange of a particle, the Higgs boson. Although the Higgs boson mass is not predicted by the theory, however it can be constrained due to its predicted couplings to the other particles. Global fits to precision electroweak data favors a light Higgs with mass below 157 GeV/c [1]. Direct Higgs searches performed at LEP set a lower limit of 114 GeV/c [2]. If this limit is included into the previous calculation, the upper limit increases to 186 GeV/c. At the Tevatron the Higgs boson can be produced in p-p̄ interactions through several processes [3]. The production cross section for Higgs mass between 100–200 GeV/c varies between ∼ 1 pb to ∼ 0.01 pb, depending on their production mechanisms. The gluon fusion (gg → H) is the dominant production process followed by the associated productions (qq̄′ → WH/ZH) and the vector boson fusion process (qq → qqH). In the low Higgs mass region (mH < 135 GeV/c), the dominant decay channel is H → bb̄ (BR ∼ 73% at mH = 115 GeV/c), followed by the H → τ τ̄ channel whose branching fraction is ∼ 10 times smaller than H → bb̄. For the Higgs boson mass above 135 GeV/c the decay channel H → W+W− becomes the dominant decay channel. Although the gluon fusion process has the largest production rate, however it is difficult to search for low mass Higgs boson in this production channel with Higgs decays in H → bb̄ due to huge QCD multi-jet background. The production and decay modes that have the best discovery sensitivities for a single search channel at low Higgs mass are the associated
120483689
DETECTING LORENTZ INVARIANCE VIOLATIONS IN THE 10 −20 RANGE
In recent years the possibility has been raised of Lorentz invariance violations arising from physics beyond the Standard Model. Some of these effects manifest themselves as small anisotropies in the velocity of light, c. By comparing the resonant frequencies of cavity modes with different spatial alignments, limits on the order δ c/c < 10-15 have been set and some further improvement can be expected. However, the largest Lorentz violations originating at the Planck scale are expected to manifest themselves as a fractional frequency variation at the 10-17 level in the absence of suppression factors. Space experiments have been proposed to approach the 10-18 level. Here we explore the possibilities for pushing further and show that it is possible in principle to reach well into the 10-20 range with existing technology. This could be done in a very quiet cryogenic environment, such as the drag-free orbiter being developed for the Satellite Test of the Equivalence Principle (STEP).