1,417 research outputs found

### Conformal fixed point, Cosmological Constant and Quintessence

We connect a possible solution for the ``cosmological constant problem'' to
the existence of a (postulated) conformal fixed point in a fundamental theory.
The resulting cosmology leads to quintessence, where the present acceleration
of the expansion of the universe is linked to a crossover in the flow of
coupling constants.Comment: More detailed discussion of quantum fluctuations,update with
WMAP-data,4 pages,LaTe

### On the origin of the difference between time and space

We suggest that the difference between time and space is due to spontaneous
symmetry breaking. In a theory with spinors the signature of the metric is
related to the signature of the Lorentz-group. We discuss a higher symmetry
that contains pseudo-orthogonal groups with arbitrary signature as subgroups.
The fundamental asymmetry between time and space arises then as a property of
the ground state rather than being put into the formulation of the theory a
priori. We show how the complex structure of quantum field theory as well as
gravitational field equations arise from spinor gravity - a fundamental spinor
theory without a metric.Comment: 4 page

### Dilatation symmetry in higher dimensions and the vanishing of the cosmological constant

A wide class of dilatation symmetric effective actions in higher dimensions
leads to a vanishing four-dimensional cosmological constant. This requires no
tuning of parameters and results from the absence of an allowed potential for
the scalar dilaton field. The field equations admit many solutions with flat
four-dimensional space and non-vanishing gauge couplings. In a more general
setting, these are candidates for asymptotic states of cosmological runaway
solutions, where dilatation symmetry is realized dynamically if a fixed point
is approached as time goes to infinity. Dilatation anomalies during the runaway
can lift the degeneracy of solutions and lead to an observable dynamical dark
energy.Comment: 4 page

### Spinor gravity and diffeomorphism invariance on the lattice

The key ingredient for lattice regularized quantum gravity is diffeomorphism
symmetry. We formulate a lattice functional integral for quantum gravity in
terms of fermions. This allows for a diffeomorphism invariant functional
measure and avoids problems of boundedness of the action. We discuss the
concept of lattice diffeomorphism invariance. This is realized if the action
does not depend on the positioning of abstract lattice points on a continuous
manifold. Our formulation of lattice spinor gravity also realizes local Lorentz
symmetry. Furthermore, the Lorentz transformations are generalized such that
the functional integral describes simultaneously euclidean and Minkowski
signature. The difference between space and time arises as a dynamical effect
due to the expectation value of a collective metric field. The quantum
effective action for the metric is diffeomorphism invariant. Realistic gravity
can be obtained if this effective action admits a derivative expansion for long
wavelengths.Comment: 13 pages, proceedings 6th Aegean Summer School, Naxos 201

### Chiral freedom and electroweak symmetry breaking

Antisymmetric tensor fields with chiral couplings to quarks and leptons may
induce spontaneous electroweak symmetry breaking in a model without a
``fundamental'' Higgs scalar. No microscopic local mass term for the chiral
tensors or ``chirons'' is allowed by the symmetries and our model exhibits only
dimensionless couplings. However, the chiral couplings are asymptotically free
and therefore generate a mass scale where they grow large. We argue that at
this scale mass terms for the chiral tensor fields are generated
non-perturbatively - the chirons appear as new massive spin one particles.
Furthermore a scalar top-antitop condensate forms, giving mass to the weak
gauge bosons and fermions. In this scenario the longstanding gauge hierarchy
problem finds a solution similar to the mass generation in QCD. We compute the
general form of the effective action for the chiral tensors and sketch several
possibilities of their detection at LHC or through precision tests of the
electroweak standard model.Comment: 30 pages, 7 figure

### Can observations look back to the beginning of inflation?

The cosmic microwave background can measure the inflaton potential only if
inflation lasts sufficiently long before the time of horizon crossing of
observable fluctuations, such that non-linear effects in the time evolution of
Green's functions lead to a loss of memory of initial conditions for the
ultraviolet tail of the spectrum. Within a derivative expansion of the quantum
effective action for an interacting scalar field we discuss the most general
solution for the correlation function, including arbitrary pure and mixed
quantum states. In this approximation no loss of memory occurs - cosmic
microwave observations see the initial spectrum at the beginning of inflation,
processed only mildly by the scale-violating effects at horizon crossing
induced by the inflaton potential.Comment: additional example and references, 5 page

### Quantum correlations in classical statistics

Quantum correlations can be naturally formulated in a classical statistical
system of infinitely many degrees of freedom. This realizes the underlying
non-commutative structure in a classical statistical setting. We argue that the
quantum correlations offer a more robust description with respect to the
precise definition of observables.Comment: 17 pages,LaTe

### Inflation, quintessence, and the origin of mass

In a unified picture both inflation and present dynamical dark energy arise
from the same scalar field. The history of the Universe describes a crossover
from a scale invariant "past fixed point" where all particles are massless, to
a "future fixed point" for which spontaneous breaking of the exact scale
symmetry generates the particle masses. The cosmological solution can be
extrapolated to the infinite past in physical time - the universe has no
beginning. This is seen most easily in a frame where particle masses and the
Planck mass are field-dependent and increase with time. In this "freeze frame"
the Universe shrinks and heats up during radiation and matter domination. In
the equivalent, but singular Einstein frame cosmic history finds the familiar
big bang description. The vicinity of the past fixed point corresponds to
inflation. It ends at a first stage of the crossover. A simple model with no
more free parameters than $\Lambda$CDM predicts for the primordial fluctuations
a relation between the tensor amplitude $r$ and the spectral index
$n,r=8.19(1-n)-0.137$. The crossover is completed by a second stage where the
beyond-standard-model sector undergoes the transition to the future fixed
point. The resulting increase of neutrino masses stops a cosmological scaling
solution, relating the present dark energy density to the present neutrino
mass. At present our simple model seems compatible with all observational
tests. We discuss how the fixed points can be rooted within quantum gravity in
a crossover between ultraviolet and infrared fixed points. Then quantum
properties of gravity could be tested both by very early and late cosmology.Comment: Extended discussion of inflation models, 38 pages, 7 figure

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