1,079 research outputs found
Leading quantum gravitational corrections to QED
We consider the leading post-Newtonian and quantum corrections to the
non-relativistic scattering amplitude of charged spin-1/2 fermions in the
combined theory of general relativity and QED. The coupled Dirac-Einstein
system is treated as an effective field theory. This allows for a consistent
quantization of the gravitational field. The appropriate vertex rules are
extracted from the action, and the non-analytic contributions to the 1-loop
scattering matrix are calculated in the non-relativistic limit. The
non-analytical parts of the scattering amplitude are known to give the long
range, low energy, leading quantum corrections, are used to construct the
leading post-Newtonian and quantum corrections to the two-particle
non-relativistic scattering matrix potential for two massive fermions with
electric charge.Comment: 14 pages, 29 figures, format RevTex
Vacuum energy: quantum hydrodynamics vs quantum gravity
We compare quantum hydrodynamics and quantum gravity. They share many common
features. In particular, both have quadratic divergences, and both lead to the
problem of the vacuum energy, which in the quantum gravity transforms to the
cosmological constant problem. We show that in quantum liquids the vacuum
energy density is not determined by the quantum zero-point energy of the phonon
modes. The energy density of the vacuum is much smaller and is determined by
the classical macroscopic parameters of the liquid including the radius of the
liquid droplet. In the same manner the cosmological constant is not determined
by the zero-point energy of quantum fields. It is much smaller and is
determined by the classical macroscopic parameters of the Universe dynamics:
the Hubble radius, the Newton constant and the energy density of matter. The
same may hold for the Higgs mass problem: the quadratically divergent quantum
correction to the Higgs potential mass term is also cancelled by the
microscopic (trans-Planckian) degrees of freedom due to thermodynamic stability
of the whole quantum vacuum.Comment: 14 pages, no figures, added section on the problem of Higgs mass,
version accepted for the special issue of JETP Letter
Unitarity and Bounds on the Scale of Fermion Mass Generation
The scale of fermion mass generation can, as shown by Appelquist and
Chanowitz, be bounded from above by relating it to the scale of unitarity
violation in the helicity nonconserving amplitude for fermion-anti-fermion
pairs to scatter into pairs of longitudinally polarized electroweak gauge
bosons. In this paper, we examine the process t tbar -> W_L W_L in a family of
phenomenologically-viable deconstructed Higgsless models and we show that scale
of unitarity violation depends on the mass of the additional vector-like
fermion states that occur in these theories (the states that are the
deconstructed analogs of Kaluza-Klein partners of the ordinary fermions in a
five-dimensional theory). For sufficiently light vector fermions, and for a
deconstructed theory with sufficiently many lattice sites (that is,
sufficiently close to the continuum limit), the Appelquist-Chanowitz bound can
be substantially weakened. More precisely, we find that, as one varies the mass
of the vector-like fermion for fixed top-quark and gauge-boson masses, the
bound on the scale of top-quark mass generation interpolates smoothly between
the Appelquist-Chanowitz bound and one that can, potentially, be much higher.
In these theories, therefore, the bound on the scale of fermion mass generation
is independent of the bound on the scale of gauge-boson mass generation. While
our analysis focuses on deconstructed Higgsless models, any theory in which
top-quark mass generation proceeds via the mixing of chiral and vector fermions
will give similar results.Comment: 12 pages, 11 eps figures included, revtex. Refrences added; wording
modified slightly to emphasize focus on top-quar
Model for self-tuning the cosmological constant
The vanishing cosmological constant in the four dimensional space-time is
obtained in a 5D Randall-Sundrum model with a brane (B1) located at . The
matter fields can be located at the brane. For settling any vacuum energy
generated at the brane to zero, we need a three index antisymmetric tensor
field with a specific form for the Lagrangian. For the self-tuning
mechanism, the bulk cosmological constant should be negative.Comment: LaTeX file of 4 pages, to appear in Phys. Rev. Let
Merging gauge coupling constants without Grand Unification
The merging of the running couplings constants of the weak, strong, and
electromagnetic fields does not require the unification of these gauge fields
at high energy. It can, in fact, be the property of a general fermionic system
in which gauge bosons are not fundamental.Comment: 11 pages, 1 figure, v3: to appear in JETP Letter
Indirect Collider Signals for Extra Dimensions
A recent suggestion that quantum gravity may become strong near the weak
scale has several testable consequences. In addition to probing for the new
large (submillimeter) extra dimensions associated with these theories via
gravitational experiments, one could search for the Kaluza Klein towers of
massive gravitons which are predicted in these models and which can interact
with the fields of the Standard Model. Here we examine the indirect effects of
these massive gravitons being exchanged in fermion pair production in \epem
annihilation and Drell-Yan production at hadron colliders. In the latter case,
we examine a novel feature of this theory, which is the contribution of gluon
gluon initiated processes to lepton pair production. We find that these
processes provide strong bounds, up to several TeV, on the string scale which
are essentially independent of the number of extra dimensions. In addition, we
analyze the angular distributions for fermion pair production with spin-2
graviton exchanges and demonstrate that they provide a smoking gun signal for
low-scale quantum gravity which cannot be mimicked by other new physics
scenarios.Comment: Corrected typos, added table and reference
Reconsidered estimates of the 10th order QED contributions to the muon anomaly
The problem of estimating the 10th order QED corrections to the muon
anomalous magnetic moment is reconsidered. The incorporation of the recently
improved contributions to the and - corrections to
within the renormalization-group inspired scheme-invariant approach
leads to the estimate . It is in good
agreement with the estimate , obtained
by Kinoshita and Nio from the numerical calculations of 2958 10-th order
diagrams, which are considered to be more important than the still uncalculated
6122 10th-order -dependent vertex graphs, and 12672 5-loop
diagrams, responsible for the mass-independent constant contribution both to
and . This confirms Kinoshita and Nio guess about dominance of
the 10-th order diagrams calculated by them. Comparisons with other estimates
of the - contributions to , which exist in the literature,
are presented.Comment: 19 pages, LaTeX, some misprints in the text and literature corrected.
Results unchaged, to appear in Phys.Rev.
Quantification of vancomycin and clindamycin in human plasma and synovial fluid applying ultra-performance liquid chromatography tandem mass spectrometry
Periprosthetic joint infection is a challenging infection involving the joint prosthesis and adjacent tissue, such as synovial fluid, synovial tissue, and bone tissue. The current treatment consists of multiple surgical revisions and long-term antibiotic therapy. Treatment failure can cause poor functional outcome and reduced quality of life. Further research on the extent of antibiotic penetration into the infected tissues is of great importance. Our work aimed to develop and validate a novel ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the determination of the commonly administered antibiotics vancomycin and clindamycin in plasma and synovial fluid. An extraction procedure consisting of zinc sulfate precipitation and dilution with eluent was used for both analytes. Chromatographic separation was performed on a Waters Acquity UPLC HSS T3 C18 column (1.8 µm, 2.1 × 100 mm), and quantification was carried out by a Waters Xevo TQ-S micro mass spectrometer. Stable isotope-labeled vancomycin-d10 served as internal standard. The method validation was performed based on the guidelines of the EMA and FDA. The calibration curves were linear over the range of 0.5–50 mg/L, with a coefficient of determination above 0.990. The validation results for precision and accuracy, specificity, matrix effects and stability were all within the acceptance range. An accurate and rapid method for the simultaneous quantification of vancomycin and clindamycin in human plasma and synovial fluid on the UPLC-MS/MS was developed, optimized and validated. The analysis has a run time of 5.2 min and 50 µL sample volume is needed. This developed method was successfully applied in eight patients with PJI and is suitable to determine the exposure of antibiotics in plasma and synovial fluid in patients during current PK/PD studies.</p
Compton and double Compton scattering processes at colliding electron-photon beams
Radiative corrections (RC) to the Compton scattering cross section are
calculated in the leading and next-to leading logarithmic approximation to the
case of colliding high energy photon-electron beams.
RC to the double Compton scattering cross section in the same experimental
set-up are calculated in the leading logarithmic approximation.
We consider the case when no pairs are created in the final state. We show
that the differential cross section can be written in the form of the Drell-Yan
process cross-section.
Numerical values of the -factor and the leading order distribution on the
scattered electron energy fraction and scattering angle are presented
Weak-Singlet Fermions: Models and Constraints
We employ data from precision electroweak tests and collider searches to
derive constraints on the possibility that weak-singlet fermions mix with the
ordinary Standard Model fermions. Our findings are presented within the context
of a theory with weak-singlet partners for all ordinary fermions and theories
in which only third-generation fermions mix with weak singlets. In addition, we
indicate how certain results can be applied more widely in theories containing
exotic fermions.Comment: 29 pages, 12 figures; added 1 reference, expanded introductio
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