1,069 research outputs found
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
Quantum Optics with Quantum Gases
Quantum optics with quantum gases represents a new field, where the quantum
nature of both light and ultracold matter plays equally important role. Only
very recently this ultimate quantum limit of light-matter interaction became
feasible experimentally. In traditional quantum optics, the cold atoms are
considered classically, whereas, in quantum atom optics, the light is used as
an essentially classical axillary tool. On the one hand, the quantization of
optical trapping potentials can significantly modify many-body dynamics of
atoms, which is well-known only for classical potentials. On the other hand,
atomic fluctuations can modify the properties of the scattered light.Comment: to be published in Laser Physics (2009
Dynamical Coupling between a Bose-Einstein Condensate and a Cavity Optical Lattice
A Bose-Einstein condensate is dispersively coupled to a single mode of an
ultra-high finesse optical cavity. The system is governed by strong
interactions between the atomic motion and the light field even at the level of
single quanta. While coherently pumping the cavity mode the condensate is
subject to the cavity optical lattice potential whose depth depends nonlinearly
on the atomic density distribution. We observe bistability already below the
single photon level and strong back-action dynamics which tunes the system
periodically out of resonance.Comment: 5 pages, 4 figure
A single Hox locus in Drosophila produces functional microRNAs from opposite DNA strands
MicroRNAs (miRNAs) are approximately 22-nucleotide RNAs that are processed from characteristic precursor hairpins and pair to sites in messages of protein-coding genes to direct post-transcriptional repression. Here, we report that the miRNA iab-4 locus in the Drosophila Hox cluster is transcribed convergently from both DNA strands, giving rise to two distinct functional miRNAs. Both sense and antisense miRNA products target neighboring Hox genes via highly conserved sites, leading to homeotic transformations when ectopically expressed. We also report sense/antisense miRNAs in mouse and find antisense transcripts close to many miRNAs in both flies and mammals, suggesting that additional sense/antisense pairs exist
All orders renormalizability of a Lorentz and CPT violating quantum electrodynamics
Renormalizability of the (minimal) single-fermion QED extension is
investigated at all orders of perturbation theory in the framework of algebraic
renormalization, a regularization-independent method. Relative to the standard
QED, new structures that could lead to gauge anomalies are identified.
Nevertheless, even if the anomaly coefficients fail to vanish in the general
case, they shall be absent provided we require invariance of the action under C
and/or PT transformations. Stability is also verified in this case, hence full
renormalizability is attained.Comment: 7 page
Ultracold atoms in optical lattices generated by quantized light fields
We study an ultracold gas of neutral atoms subject to the periodic optical
potential generated by a high- cavity mode. In the limit of very low
temperatures, cavity field and atomic dynamics require a quantum description.
Starting from a cavity QED single atom Hamiltonian we use different routes to
derive approximative multiparticle Hamiltonians in Bose-Hubbard form with
rescaled or even dynamical parameters. In the limit of large enough cavity
damping the different models agree. Compared to free space optical lattices,
quantum uncertainties of the potential and the possibility of atom-field
entanglement lead to modified phase transition characteristics, the appearance
of new phases or even quantum superpositions of different phases. Using a
corresponding effective master equation, which can be numerically solved for
few particles, we can study time evolution including dissipation. As an example
we exhibit the microscopic processes behind the transition dynamics from a Mott
insulator like state to a self-ordered superradiant state of the atoms, which
appears as steady state for transverse atomic pumping.Comment: 17 pages, 10 figures, Published versio
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