11,027 research outputs found
Power-law intensity distribution in -decay cascades -- Nuclear Structure as a Scale-Free Random Network
By modeling the transition paths of the nuclear -decay cascade using
a scale-free random network, we uncover a universal power-law distribution of
-ray intensity , with the -ray
intensity of each transition. This property is consistently observed for all
datasets with a sufficient number of -ray intensity entries in the
National Nuclear Data Center database, regardless of the reaction type or
nuclei involved. In addition, we perform numerical simulations which support
the model's predictions of level population density
Quintessence, scalar-tensor theories and non-Newtonian gravity
We discuss some of the issues which we encounter when we try to invoke the
scalar-tensor theories of gravitation as a theoretical basis of quintessence.
One of the advantages of appealing to these theories is that they allow us to
implement the scenario of a ``decaying cosmological constant,'' which offers a
reasonable understanding of why the observed upper bound of the cosmological
constant is smaller than the theoretically natural value by as much as 120
orders of magnitude. In this context, the scalar field can be a candidate of
quintessence in a broader sense. We find, however, a serious drawback in the
prototype Brans-Dicke model with added; a static universe in the
physical conformal frame which is chosen to have constant particle masses. We
propose a remedy by modifying the matter coupling of the scalar field taking
advantage of scale invariance and its breakdown through quantum anomaly. By
combining this with a conjecture on another cosmological constant problem
coming from the vacuum energy of matter fields, we expect a possible link
between quintessence and non-Newtonian gravity featuring violation of Weak
Equivalence Principle and intermediate force range, likely within the
experimental constraints. A new prediction is also offered on the
time-variability of the gravitational constant.Comment: 12 pages LaTex including 1 eps figur
Gravity is controlled by cosmological constant
We discuss a Randall-Sundrum-type two D-braneworld model in which D-branes
possess different values of the tensions from those of the charges, and derive
an effective gravitational equation on the branes. As a consequence, the
Einstein-Maxwell theory is realized together with the non-zero cosmological
constant. Here an interesting point is that the effective gravitational
constant is proportional to the cosmological constant. If the distance between
two D-branes is appropriately tuned, the cosmological constant can have a
consistent value with the current observations. From this result we see that,
in our model, the presence of the cosmological constant is naturally explained
by the presence of the effective gravitational coupling of the Maxwell field on
the D-brane.Comment: 10 page
Remarks on flavor-neutrino propagators and oscillation formulae
We examine the general structure of the formulae of neutrino oscillations
proposed by Blasone and Vitiello(BV). Reconstructing their formulae with the
retarded propagators of the flavor neutrino fields for the case of many
flavors, we can get easily the formulae which satisfy the suitable boundary
conditions and are independent of arbitrary mass parameters ,
as is obtained by BV for the case of two flavors. In this two flavor case, our
formulae reduce to those obtained by BV under -invariance condition.
Furthermore, the reconstructed probabilities are shown to coincide with those
derived with recourse to the mass Hilbert space which is
unitarily inequivalent to the flavor Hilbert space . Such a
situation is not found in the corresponding construction a la BV. Then the new
factors in the BV's formulae, which modify the usual oscill ation formulae, are
not the trace of the flavor Hilbert space construction, but come from
Bogolyubov transformation among the operators of spin-1/2 ne utrino with
different masses.Comment: revtex, 16 page
Fully fault tolerant quantum computation with non-deterministic gates
In certain approaches to quantum computing the operations between qubits are
non-deterministic and likely to fail. For example, a distributed quantum
processor would achieve scalability by networking together many small
components; operations between components should assumed to be failure prone.
In the logical limit of this architecture each component contains only one
qubit. Here we derive thresholds for fault tolerant quantum computation under
such extreme paradigms. We find that computation is supported for remarkably
high failure rates (exceeding 90%) providing that failures are heralded,
meanwhile the rate of unknown errors should not exceed 2 in 10^4 operations.Comment: 5 pages, 3 fig
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