1,077 research outputs found
Perturbative Quantum Field Theory at Positive Temperatures: An Axiomatic Approach
It is shown that the perturbative expansions of the correlation functions of
a relativistic quantum field theory at finite temperature are uniquely
determined by the equations of motion and standard axiomatic requirements,
including the KMS condition. An explicit expression as a sum over generalized
Feynman graphs is derived. The canonical formalism is not used, and the
derivation proceeds from the beginning in the thermodynamic limit. No doubling
of fields is invoked. An unsolved problem concerning existence of these
perturbative expressions is pointed out.Comment: 17pages Late
Infrared limit in external field scattering
Scattering of electrons/positrons by external classical electromagnetic wave
packet is considered in infrared limit. In this limit the scattering operator
exists and produces physical effects, although the scattering cross-section is
trivial.Comment: 12 pages; published version; minor corrections; comments adde
Infrared cutoffs and the adiabatic limit in noncommutative spacetime
We discuss appropriate infrared cutoffs and their adiabatic limit for field
theories on the noncommutative Minkowski space in the Yang-Feldman formalism.
In order to do this, we consider a mass term as interaction term. We show that
an infrared cutoff can be defined quite analogously to the commutative case and
that the adiabatic limit of the two-point function exists and coincides with
the expectation, to all orders.Comment: 19 page
Removal of violations of the Master Ward Identity in perturbative QFT
We study the appearance of anomalies of the Master Ward Identity, which is a
universal renormalization condition in perturbative QFT. The main insight of
the present paper is that any violation of the Master Ward Identity can be
expressed as a LOCAL interacting field; this is a version of the well-known
Quantum Action Principle of Lowenstein and Lam. Proceeding in a proper field
formalism by induction on the order in , this knowledge about the
structure of possible anomalies as well as techniques of algebraic
renormalization are used to remove possible anomalies by finite
renormalizations. As an example the method is applied to prove the Ward
identities of the O(N) scalar field model.Comment: 51 pages. v2: a few formulations improved, one reference added. v3: a
few mistakes corrected and one additional reference. v4: version to be
printed in Reviews in Mathematical Physic
BFKL approach and 2->5 MHV amplitude
We study MHV amplitude for the 2 -> 5 scattering in the multi-Regge
kinematics. The Mandelstam cut correction to the BDS amplitude is calculated in
the leading logarithmic approximation (LLA) and the corresponding remainder
function is given to any loop order in a closed integral form. We show that the
LLA remainder function at two loops for 2 -> 5 amplitude can be written as a
sum of two 2 -> 4 remainder functions due to recursive properties of the
leading order impact factors. We also make some generalizations for the MHV
amplitudes with more external particles. The results of the present study are
in agreement with all leg two loop symbol derived by Caron-Huot as shown in a
parallel paper of one of the authors with collaborators.Comment: 24 pages, 17 figure
Air-flow sensitive hairs: boundary layers in oscillatory flows around arthropod appendages
The aim of this work is to characterize the boundary layer over small appendages in insects in longitudinal and transverse oscillatory flows. The problem of immediate interest is the early warning system in crickets perceiving flying predators using air-flow-sensitive hairs on cerci, two long appendages at their rear. We studied both types of oscillatory flows around small cylinders using stroboscopic micro-particle image velocimetry as a function of flow velocity and frequency. Theoretical predictions are well fulfilled for both longitudinal and transverse flows. Transverse flow leads to higher velocities than longitudinal flow in the boundary layer over a large range of angles between flow and cylinder. The strong spatial heterogeneity of flow velocities around filiform-shaped appendages is a rich source of information for different flow-sensing animals. Our results suggest that crickets could perceive the direction of incoming danger by having air-flow-sensitive hairs positioned around their entire cerci. Implications for biomimetic flow-sensing MEMS are also presented
Mandelstam cuts and light-like Wilson loops in N=4 SUSY
We perform an analytic continuation of the two-loop remainder function for
the six-point planar MHV amplitude in N=4 SUSY, found by Goncharov, Spradlin,
Vergu and Volovich from the light-like Wilson loop representation. The
remainder function is continued into a physical region, where all but two
energy invariants are negative. It turns out to be pure imaginary in the
multi-Regge kinematics, which is in an agreement with the predictions based on
the Steinmann relations for the Regge poles and Mandelstam cut contributions.
The leading term reproduces correctly the expression calculated by one of the
authors in the BFKL approach, while the subleading term presents a result, that
was not yet found with the use of the unitarity techniques. This supports the
applicability of the Wilson loop approach to the planar MHV amplitudes in N=4
SUSY.Comment: 11 pages, 4 figure
Complex regulation of CREB-binding protein by homeodomain-interacting protein kinase 2.
CREB-binding protein (CBP) and p300 are transcriptional coactivators involved in numerous biological processes that affect cell growth, transformation, differentiation, and development. In this study, we provide evidence of the involvement of homeodomain-interacting protein kinase 2 (HIPK2) in the regulation of CBP activity. We show that HIPK2 interacts with and phosphorylates several regions of CBP. We demonstrate that serines 2361, 2363, 2371, 2376, and 2381 are responsible for the HIPK2-induced mobility shift of CBP C-terminal activation domain. Moreover, we show that HIPK2 strongly potentiates the transcriptional activity of CBP. However, our data suggest that HIPK2 activates CBP mainly by counteracting the repressive action of cell cycle regulatory domain 1 (CRD1), located between amino acids 977 and 1076, independently of CBP phosphorylation. Our findings thus highlight a complex regulation of CBP activity by HIPK2, which might be relevant for the control of specific sets of target genes involved in cellular proliferation, differentiation and apoptosis
Spacelike localization of long-range fields in a model of asymptotic electrodynamics
A previously proposed algebra of asymptotic fields in quantum electrodynamics
is formulated as a net of algebras localized in regions which in general have
unbounded spacelike extension. Electromagnetic fields may be localized in
`symmetrical spacelike cones', but there are strong indications this is not
possible in the present model for charged fields, which have tails extending in
all space directions. Nevertheless, products of appropriately `dressed' fermion
fields (with compensating charges) yield bi-localized observables.Comment: 29 pages, accepted for publication in Annales Henri Poincar\'
Infra-Red Asymptotic Dynamics of Gauge Invariant Charged Fields: QED versus QCD
The freedom one has in constructing locally gauge invariant charged fields in
gauge theories is analyzed in full detail and exploited to construct, in QED,
an electron field whose two-point function W(p), up to the fourth order in the
coupling constant, is normalized with on-shell normalization conditions and is,
nonetheless, infra-red finite; as a consequence the radiative corrections
vanish on the mass shell and the free field singularity is
dominant, although, in contrast to quantum field theories with mass gap, the
eigenvalue of the mass operator is not isolated. The same construction,
carried out for the quark in QCD, is not sufficient for cancellation of
infra-red divergences to take place in the fourth order. The latter
divergences, however, satisfy a simple factorization equation. We speculate on
the scenario that could be drawn about infra-red asymptotic dynamics of QCD,
should this factorization equation be true in any order of perturbation theory.Comment: 30 pages, RevTex, 8 figures included using graphic
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