150 research outputs found
Physical Tuning and Naturalness
We present a radically new proposal for the solution of the
naturalness/hierarchy problem, where the fine-tuning of the Higgs mass finds
its physical explanation and the well-known multiplicative renormalization of
the usual perturbative approach emerges as an IR property of the
non-perturbative running of the mass.Comment: 7 pages, 4 figure
The Price of an Exact, Gauge-Invariant RG-Flow Equation
We combine old ideas about exact renormalization-group-flow (RGF) equations
with the Vilkovisky-De Witt (VDW) approach to reparametrization invariant
effective actions and arrive at a new, exact, gauge-invariant RGF equation. The
price to be paid for such a result is that both the action and the RGF equation
depend explicitly upon the base point (in field space) needed for the VDW
construction. We briefly discuss the complications originating from this fact
and possible ways to overcome them.Comment: 12 pages. To appear in Phys. Lett.
Dilution of zero point energies in the cosmological expansion
The vacuum fluctuations of all quantum fields filling the universe are
supposed to leave enormous energy and pressure contributions which are
incompatible with observations. It has been recently suggested that, when the
effective nature of quantum field theories is properly taken into account,
vacuum fluctuations behave as a relativistic gas rather than as a cosmological
constant. Accordingly, zero-point energies are tremendously diluted by the
universe expansion but provide an extra contribution to radiation energy.
Ongoing and future cosmological observations could offer the opportunity to
scrutinize this scenario. The presence of such additional contribution to
radiation energy can be tested by using primordial nucleosynthesis bounds or
measured on Cosmic Background Radiation anisotropy.Comment: 8 pages, no figures. Submitted the 17th of March to Modern Physics
Letters
Comment on "Feynman Effective Classical Potential in the Schrodinger Formulation"
We comment on the paper "Feynman Effective Classical Potential in the
Schrodinger Formulation"[Phys. Rev. Lett. 81, 3303 (1998)]. We show that the
results in this paper about the time evolution of a wave packet in a double
well potential can be properly explained by resorting to a variational
principle for the effective action. A way to improve on these results is also
discussed.Comment: 1 page, 2eps figures, Revte
Instability induced renormalization
It is pointed out that models with condensates have nontrivial renormalization group flow on the tree level. The infinitesimal form of the tree level renormalization group equation is obtained and solved numerically for the φ 4 model in the symmetry broken phase. We find an attractive infrared fixed point that eliminates the metastable region and reproduces the Maxwell construction. © 1999 Elsevier Science B.V. All rights reserved
Renormalization Group in Quantum Mechanics
We establish the renormalization group equation for the running action in the
context of a one quantum particle system. This equation is deduced by
integrating each fourier mode after the other in the path integral formalism.
It is free of the well known pathologies which appear in quantum field theory
due to the sharp cutoff. We show that for an arbitrary background path the
usual local form of the action is not preserved by the flow. To cure this
problem we consider a more general action than usual which is stable by the
renormalization group flow. It allows us to obtain a new consistent
renormalization group equation for the action.Comment: 20 page
Finite-momentum Bose-Einstein condensates in shaken 2D square optical lattices
We consider ultracold bosons in a 2D square optical lattice described by the
Bose-Hubbard model. In addition, an external time-dependent sinusoidal force is
applied to the system, which shakes the lattice along one of the diagonals. The
effect of the shaking is to renormalize the nearest-neighbor hopping
coefficients, which can be arbitrarily reduced, can vanish, or can even change
sign, depending on the shaking parameter. It is therefore necessary to account
for higher-order hopping terms, which are renormalized differently by the
shaking, and introduce anisotropy into the problem. We show that the
competition between these different hopping terms leads to finite-momentum
condensates, with a momentum that may be tuned via the strength of the shaking.
We calculate the boundaries between the Mott-insulator and the different
superfluid phases, and present the time-of-flight images expected to be
observed experimentally. Our results open up new possibilities for the
realization of bosonic analogs of the FFLO phase describing inhomogeneous
superconductivity.Comment: 7 pages, 7 figure
Effective action and the quantum equation of motion
We carefully analyse the use of the effective action in dynamical problems,
in particular the conditions under which the equation \frac{\delta \Ga}
{\delta \phi}=0 can be used as a quantum equation of motion, and the relation
between the asymptotic states involved in the definition of \Ga and the
initial state of the system. By considering the quantum mechanical example of a
double-well potential, where we can get exact results for the time evolution of
the system, we show that an approximation to the effective potential in the
quantum equation of motion that correctly describes the dynamical evolution of
the system is obtained with the help of the wilsonian RG equation (already at
the lowest order of the derivative expansion), while the commonly used one-loop
effective potential fails to reproduce the exact results.Comment: 28 pages, 13 figures. Revised version to appear in The European
Physical Journal
Dark energy and Josephson junctions
It has been recently claimed that dark energy can be (and has been) observed
in laboratory experiments by measuring the power spectrum of the
noise current in a resistively shunted Josephson junction and that in new
dedicated experiments, which will soon test a higher frequency range,
should show a deviation from the linear rising observed in the
lower frequency region because higher frequencies should not contribute to dark
energy. Based on previous work on theoretical aspects of the
fluctuation-dissipation theorem, we carefully investigate these issues and show
that these claims are based on a misunderstanding of the physical origin of the
spectral function . According to our analysis, dark energy has
never been (and will never be) observed in Josephson junctions experiments. We
also predict that no deviation from the linear rising behavior of
will be observed in forthcoming experiments. Our findings provide new (we
believe definite) arguments which strongly support previous criticisms.Comment: 9 pages, no figure
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