Effect of the oscillations in the photon distribution of a squeezed field on the fluorescence spectrum of the Jaynes–Cummings model

Following the scheme proposed by Eberly and Wodkiewicz for the physical spectrum, we calculate the fluorescence spectrum of the Jaynes–Cummings model when the two-level system interacts with an electromagnetic field that initially is in a squeezed coherent state. We show the appearing of “ringing lines” in the fluorescence spectrum that are echoes of the oscillations in the photon distribution of the compressed field. These ringing lines may be a similar effect as the ringing revivals of the atomic inversion that are a signature of squeezed states.

The Fröhlich-Morchio-Strocchi mechanism and quantum gravity

Taking manifest invariance under both gauge symmetry and diffeomorphisms as a guiding principle physical objects are constructed for Yang-Mills-Higgs theory coupled to quantum gravity. These objects are entirely classified by quantum numbers defined in the tangent space. Applying the Fröhlich-Morchio-Strocchi mechanism to these objects reveals that they coincide with ordinary correlation functions in quantum-field theory, if quantum fluctuations of gravity and curvature become small. Taking these descriptions literally exhibits how quantum gravity fields need to dress quantum fields to create physical objects, i. e. giving a graviton component to ordinary observed particles. The same mechanism provides access to the physical spectrum of pure gravitational degrees of freedom.

SU(3) breaking and the pseudo-scalar spectrum in multi-taste QCD

Using the Sigma model to explore the lowest order pseudo-scalar spectrum with SU(3) breaking, this talk considers an additional exact “taste” symmetry to mimic species doubling. Rooting replicas of a valid approach such as Wilson fermions reproduces the desired physical spectrum. In contrast, extra symmetries of the rooted staggered approach leave spurious states and a flavor dependent taste multiplicity.

A study of how the particle spectra of SU(N) gauge theories with a fundamental Higgs emerge

In gauge theories, the physical, experimentally observable spectrum consists only of gauge-invariant states. In the standard model the Fröhlich-Morchio-Strocchi mechanism shows that these states can be adequately mapped to the gauge-dependent elementary W, Z, Higgs, and fermions. In theories with a more general gauge group and Higgs sector, appearing in various extensions of the standard model, this has not to be the case. In this work we determine analytically the physical spectrum of SU(N > 2) gauge theories with a Higgs field in the fundamental representation. We show that discrepancies between the spectrum predicted by perturbation theory and the observable physical spectrum arise. We confirm these analytic findings with lattice simulations for N = 3.

Where have all the Goldstone bosons gone?

According to a commonly held view of spontaneously broken symmetry in gauge theories, troublesome Nambu–Goldstone bosons are effectively eliminated by turning into longitudinal modes of a massive vector meson. This note shows that, this is not in fact, a consistent view of the role of Nambu–Goldstone bosons in such theories. These particles necessarily appear as gauge excitations, whenever they are formulated in a manifestly covariant gauge. The radiation gauge provides therefore the dual advantage of circumventing the Goldstone theorem and making evident the disappearance of these particles from the physical spectrum.

PHYSICAL SPECTRUM FROM CONFINED EXCITATIONS IN A YANG–MILLS-INSPIRED TOY MODEL

We study a toy model for an interacting scalar field theory in which the fundamental excitations are confined in the sense of having unphysical, positivity-violating propagators, a fact tracing back to a decomposition of these in propagators with complex conjugate mass poles (the so-called i-particles). Similar two-point functions show up in certain approaches to gluon or quark propagators in Yang–Mills gauge theories. We investigate the spectrum of our model and show that suitable composite operators may be constructed having a well-defined Källén–Lehmann spectral representation, thus allowing for a particle interpretation. These physical excitations would correspond to the "mesons" of the model, the latter being bound states of two unphysical i-particles. The meson mass is explicitly estimated from the pole emerging in a resummed class of diagrams. The main purpose of this paper is thus to explicitly verify how a real mass pole can and does emerge out of constituent i-particles that have complex masses.

STANDARD MODEL WITH COSMOLOGICALLY BROKEN QUANTUM SCALE INVARIANCE

We consider a locally scale invariant extension of the Standard Model of particle physics and argue that it fits both the particle and cosmological observations. The model is scale invariant both classically and quantum mechanically. The scale invariance is broken (or hidden) by a mechanism which we refer to as cosmological symmetry breaking. This produces all the dimensionful parameters in the theory. The cosmological constant or dark energy is a prediction of the theory and can be calculated systematically order by order in perturbation theory. It is expected to be finite at all orders. The model does not suffer from the hierarchy problem due to the absence of scalar particles, including the Higgs, from the physical spectrum.