40 research outputs found
Chiral tensor fields and spontaneous breaking of Lorentz symmetry
Antisymmetric tensor fields interacting with quarks and leptons have been
proposed as a possible solution to the gauge hierarchy problem. We compute the
one-loop beta function for a quartic self-interaction of the chiral
antisymmetric tensor fields. Fluctuations of the top quark drive the
corresponding running coupling to a negative value as the renormalization scale
is lowered. This may indicate a non-vanishing expectation value of the tensor
field, and thus a spontaneous breaking of Lorentz invariance. Settling this
issue will need the inclusion of tensor loops.Comment: 15 pages, 4 figure
Asymptotically free four-fermion interactions and electroweak symmetry breaking
We investigate the fermions of the standard model without a Higgs scalar.
Instead, we consider a non-local four-quark interaction in the tensor channel
which is characterized by a single dimensionless coupling . Quantization
leads to a consistent perturbative expansion for small . The running of
is asymptotically free and therefore induces a non-perturbative scale
, in analogy to the strong interactions. We argue that
spontaneous electroweak symmetry breaking is triggered at a scale where
grows large and find the top quark mass of the order of . We also
present a first estimate of the effective Yukawa coupling of a composite Higgs
scalar to the top quark, as well as the associated mass ratio between the top
quark and the W boson.Comment: 24 page
The cosmological constant problem in codimension-two brane models
We discuss the possibility of a dynamical solution to the cosmological
constant problem in the contaxt of six-dimensional Einstein-Maxwell theory. A
definite answer requires an understanding of the full bulk cosmology in the
early universe, in which the bulk has time-dependent size and shape. We comment
on the special properties of codimension two as compared to higher
codimensions.Comment: 11 page
Dark energy cosmologies for codimension-two branes
A six-dimensional universe with two branes in the "football-shaped" geometry
leads to an almost realistic cosmology. We describe a family of exact solutions
with time dependent characteristic size of internal space. After a short
inflationary period the late cosmology is either of quintessence type or turns
to a radiation dominated Friedmann universe where the cosmological constant
appears as a free integration constant of the solution. The radiation dominated
universe with relativistic fermions is analyzed in detail, including its
dimensional reduction.Comment: 18 page
Holographic Branes
We discuss the properties of codimension-two branes and compare them to
codimension-one branes. In particular, we show that for deficit angle branes
the brane energy momentum tensor is uniquely related to integration constants
in the bulk solution. We investigate chiral fermions whose wave functions are
concentrated on the brane, while all their properties in the effective
four-dimensional world can be inferred from the tail of the wave function in
the bulk, thereby realizing a holographic principle. We propose holographic
branes for which the knowledge of the bulk geometry is sufficient for the
computation of all relevant properties of the observable particles,
independently of the often unknown detailed physics of the branes.Comment: 13 pages, references adde
A Minimal Length from the Cutoff Modes in Asymptotically Safe Quantum Gravity
Within asymptotically safe Quantum Einstein Gravity (QEG), the quantum
4-sphere is discussed as a specific example of a fractal spacetime manifold.
The relation between the infrared cutoff built into the effective average
action and the corresponding coarse graining scale is investigated. Analyzing
the properties of the pertinent cutoff modes, the possibility that QEG
generates a minimal length scale dynamically is explored. While there exists no
minimal proper length, the QEG sphere appears to be "fuzzy" in the sense that
there is a minimal angular separation below which two points cannot be resolved
by the cutoff modes.Comment: 26 pages, 1 figur
Scale-dependent metric and causal structures in Quantum Einstein Gravity
Within the asymptotic safety scenario for gravity various conceptual issues
related to the scale dependence of the metric are analyzed. The running
effective field equations implied by the effective average action of Quantum
Einstein Gravity (QEG) and the resulting families of resolution dependent
metrics are discussed. The status of scale dependent vs. scale independent
diffeomorphisms is clarified, and the difference between isometries implemented
by scale dependent and independent Killing vectors is explained. A concept of
scale dependent causality is proposed and illustrated by various simple
examples. The possibility of assigning an "intrinsic length" to objects in a
QEG spacetime is also discussed.Comment: 52 page