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Dennis D. Dietrich

Publications and source records attributed to Dennis D. Dietrich.

At least 37 records · Page 2Linked to original sources
arXiv2009

Linear confinement without dilaton in bottom-up holography for walking technicolour

In PRD78(2008)055005 [arXiv:0805.1503 [hep-ph]] and PRD79(2009)075004 [arXiv:0809.1324 [hep-ph]], we constructed a holographic description of walking technicolour theories using both a hard- and a soft-wall model. Here, we show that the dilaton field becomes phenomenologically irrelevant for the spectrum of spin-one resonances once a term is included in the Lagrangian that mixes the Goldstone bosons and the longitudinal components of the axial vector mesons. We show how this mixing affects our previous results and we make predictions about how this description of technicolour can be tested.

hep-ph↗
arXiv2009

On invariants for particle propagation in non-Abelian fields

Characterising the propagation of particles in an external non-Abelian field only in terms of invariants constructed from its field tensor is not always sufficient, especially, in many analytically tractable and phenomenologically interesting cases.

hep-th↗
arXiv2009

Concerning gauge field fluctuations around classical configurations

We treat the fluctuations of non-Abelian gauge fields around a classical configuration by means of a transformation from the Yang--Mills gauge field to a homogeneously transforming field variable. We use the formalism to compute the effective action induced by these fluctuations in a static background without Wu--Yang ambiguity.

hep-th↗
arXiv2009

Pion masses in quasiconformal gauge field theories

We study modifications to Weinberg-like sum rules in quasiconformal gauge field theories. Beyond the two Weinberg sum rules and the oblique S parameter we study the pion mass and the X parameter. Especially, we evaluate the pion mass for walking technicolour theories, in particular also minimal walking technicolour, and find contributions of the order of up to several hundred GeV.

hep-ph↗
arXiv2008

Generalised bottom-up holography and walking technicolour

In extradimensional holographic approaches the flavour symmetry is gauged in the bulk, that is, treated as a local symmetry. Imposing such a local symmetry admits fewer terms coupling the (axial) vectors and (pseudo)scalars than if a global symmetry is imposed. The latter is the case in standard low-energy effective Lagrangians. Here we incorporate these additional, a priori only globally invariant terms into a holographic treatment by means of a Stueckelberg completion and alternatively by means of a Legendre transformation. This work was motivated by our investigations concerning dynamical electroweak symmetry breaking by walking technicolour and we apply our findings to these theories.

hep-ph↗
arXiv2008

Constraining vectors and axial-vectors in walking technicolour by a holographic principle

We use a holographic principle to study the low-energy spectrum of walking technicolour models. In particular, we predict the masses of the axial vectors as well as the decay constants of vectors and axial vectors as functions of the mass of the techni-rho. Given that there are very few nonperturbative techniques to study strongly coupled theories, using holography might provide us with insight into how to constrain the parameters of the low-energy effective action of walking technicolour models. We also compare our results with findings from other setups.

hep-ph↗
arXiv2008

Electroweak symmetry breaking in other terms

We analyse descriptions of electroweak symmetry breaking in terms of ultralocal antisymmetric tensor fields and gauge-singlet geometric variables, respectively; in particular, the Weinberg--Salam model and, ultimately, dynamical electroweak symmetry breaking by technicolour theories with enhanced symmetry groups. Our motivation is to unveil the manifestly gauge invariant structure of the different realisations. We find, for example, parallels to different types of torsion.

hep-th↗
arXiv2007

Gutzwiller's Trace Formula and Vacuum Pair Production

We propose a new application of the Gutzwiller trace formula formalism, to give a compact expression for the semiclassical vacuum pair production rate in quantum electrodynamics, for general inhomogeneous electromagnetic background fields.

hep-th↗
arXiv2007

Gauge invariance in gravity-like descriptions of massive gauge field theories

We discuss gravity-like formulations of massive Abelian and non-Abelian gauge field theories in four space-time dimensions with particular emphasis on the issue of gauge invariance. Alternative descriptions in terms of antisymmetric tensor fields and geometric variables, respectively, are analysed. In both approaches Stückelberg degrees of freedom factor out. We also demonstrate, in the Abelian case, that the massless limit for the gauge propagator, which does not exist in the vector potential formulation, is well-defined for the antisymmetric tensor fields.

hep-th↗
arXiv2007

Perturbative gauge theory in a background

Motivated by the gluon condensate in QCD we study the perturbative expansion of a gauge theory in the presence of gauge bosons of vanishing momentum, in the specific case of an abelian theory. The background is characterised by a dimensionful parameter $Λ$ affecting only the on-shell prescription of the free (abelian) gluon propagator. When summed to all orders in $gΛ$ the modification is equivalent to evaluating standard Green functions in a pure gauge field with an imaginary gauge parameter $\propto Λ$. We show how to calculate the corresponding dressed Green functions, which are Poincare and gauge covariant. We evaluate the expressions for the dressed quark and $q \bar q$ propagators, imposing as boundary condition that they approach the standard perturbative form in the short-distance limit ($|p^2|\to\infty$). The on-shell ($p^2=m^2$) pole of the free quark propagator is removed for any $Λ> 0$, and replaced by a discontinuity which vanishes exponentially with $p^2$. The dressing introduces an effective interaction between quarks and antiquarks which is enhanced at low relative 3-momentum. Further study should allow to identify the (bound) eigenstates of propagation and determine whether they define a unitary S-matrix. When the quark mass is zero there is a euclidean propagator solution which breaks chiral symmetry spontaneously. We study some aspects of the massless pion contribution to axial vector correlators and derive the $πq \bar q$ form factor.

hep-ph↗
arXiv2006

Walking in the SU(N)

We study the phase diagram as function of the number of colours and flavours of asymptotically free non-supersymmetric theories with matter in higher dimensional representations of arbitrary SU(N) gauge groups. Since matter in higher dimensional representations screens more than in the fundamental a general feature is that a lower number of flavours is needed to achieve a near-conformal theory. We study the spectrum of the theories near the fixed point and consider possible applications of our analysis to the dynamical breaking of the electroweak symmetry.

hep-ph↗
arXiv2005

Slowly decaying classical fields, unitarity, and gauge invariance

In classical external gauge fields that fall off less fast than the inverse of the evolution parameter (time) of the system the implementability of a unitary perturbative scattering operator ($S$-matrix) is not guaranteed, although the field goes to zero. The importance of this point is exposed for the counter-example of low-dimensionally expanding systems. The issues of gauge invariance and of the interpretation of the evolution at intermediate times are also intricately linked to that point.

hep-th↗
arXiv2005

Non-abelian vector backgrounds with restored Lorentz invariance

The influence of vector backgrounds with restored Lorentz invariance on non-abelian gauge field theories is studied. Lorentz invariance is ensured by taking the average over a Lorentz invariant ensemble of background vectors. Like in the abelian case [hep-ph/0506210], the propagation of fermions is suppressed over long distances. Contrary to the fermionic sector, pure gauge configurations of the background suppress the long-distance propagation of the bosons only partially, i.e. not beyond the leading contribution for a large number of colours.

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arXiv2005

Lorentz invariant ensembles of vector backgrounds

We consider gauge field theories in the presence of ensembles of vector backgrounds. While Lorentz invariance is explicitely broken in the presence of any single background, here, the Lorentz invariance of the theory is restored by averaging over a Lorentz invariant ensemble of backgrounds, i.e. a set of background vectors that is mapped onto itself under Lorentz transformations. This framewkork is used to study the effects of a non-trivial but Lorentz invariant vacuum structure or mass dimension two vector condensates by identifying the background with a shift of the gauge field. Up to now, the ensembles used in the literature comprise configurations corresponding to non-zero field tensors together with such with vanishing field strength. We find that even when constraining the ensembles to pure gauge configurations, the usual high-energy degrees of freedom are removed from the spectrum of asymptotic states in the presence of said backgrounds in euclidean and in Minkowski space. We establish this result not only for the propagators to all orders in the background and otherwise at tree level but for the full propagator.

hep-ph↗
arXiv2005

Saturation momentum at fixed and running QCD coupling

A relationship, linking the saturation momentum in the case of fixed and running QCD coupling, respectively, is derived from the Balitsky-Kovchegov equation. It relies on the linear instability of the evolution equation in the dilute regime. The leading orders of the saturation momenta are mapped onto each other exactly. For subleading terms a qualitative correspondence is achieved with a relative error going to zero for large rapidities. The relationship can also be derived for the Balitsky-Kovchegov equation with a cutoff accounting for low-density effects and is satisfied by the corresponding isoline functions. Further implications arise for the existence of travelling-wave solutions in the two situations.

hep-ph↗
arXiv2004

Gluon propagation in space-time dependent fields

The propagator for gluons in a space-time dependent field is derived. This is accomplished by solving the equation of motion for the gluonic Green's functions. Subsequently a relationship between the quark and the gluon propagator is presented. With its help characteristics of the bosonic propagator can be obtained from those of the fermionic and vice versa. Finally, this relation is discussed for the special case of ultrarelativistic collisions in the semiclassical limit.

hep-ph↗
arXiv2004

Fermion production in classical fields

The creation of quark-antiquark pairs by vacuum polarisation in the presence of classical fields is studied based on their propagators in the background. Especially the issue of gauge invariance and particularities of particle production in ultrarelativistic collider experiments are discussed.

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