20,074 research outputs found
Theory of Complex Scattering Lengths
We derive a generalized Low equation for the T-matrix appropriate for complex
atom-molecule interaction. The properties of this new equation at very low
energies are studied and the complex scattering length and effective range are
derived.Comment: 9 page
The resultant parameters of effective theory
This is the 4-th paper in the series devoted to a systematic study of the
problem of mathematically correct formulation of the rules needed to manage an
effective field theory. Here we consider the problem of constructing the full
set of essential parameters in the case of the most general effective
scattering theory containing no massless particles with spin J > 1/2. We
perform the detailed classification of combinations of the Hamiltonian coupling
constants and select those which appear in the expressions for renormalized
S-matrix elements at a given loop order.Comment: 21 pages, 4 LaTeX figures, submitted to Phys. Rev.
Asymptotically Safe Lorentzian Gravity
The gravitational asymptotic safety program strives for a consistent and
predictive quantum theory of gravity based on a non-trivial ultraviolet fixed
point of the renormalization group (RG) flow. We investigate this scenario by
employing a novel functional renormalization group equation which takes the
causal structure of space-time into account and connects the RG flows for
Euclidean and Lorentzian signature by a Wick-rotation. Within the
Einstein-Hilbert approximation, the -functions of both signatures
exhibit ultraviolet fixed points in agreement with asymptotic safety.
Surprisingly, the two fixed points have strikingly similar characteristics,
suggesting that Euclidean and Lorentzian quantum gravity belong to the same
universality class at high energies.Comment: 4 pages, 2 figure
The UV behavior of Gravity at Large N
A first step in the analysis of the renormalizability of gravity at Large N
is carried on. Suitable resummations of planar diagrams give rise to a theory
in which there is only a finite number of primitive superficially divergent
Feynman diagrams. The mechanism is similar to the the one which makes
renormalizable the 3D Gross-Neveu model at large N. Some potential problems in
fulfilling the Slavnov-Taylor and the Zinn-Justin equations are also pointed
out.Comment: 17 pages, 9 figures. To appear on Phys. Rev. D. Two more references,
further technical details and the discussion of the KLT relations at large N
have been include
Effective Field Theory for Inflation
The methods of effective field theory are used to study generic theories of
inflation with a single inflaton field. For scalar modes, the leading
corrections to the correlation function are found to be purely of
the -inflation type. For tensor modes the leading corrections to the
correlation function arise from terms in the action that are quadratic in the
curvature, including a parity-violating term that makes the propagation of
these modes depend on their helicity. These methods are also briefly applied to
non-generic theories of inflation with an extra shift symmetry, as in so-called
ghost inflation.Comment: 14 pages, Latex, references added and minor additions and corrections
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Note on the thermal history of decoupled massive particles
This note provides an alternative approach to the momentum decay and thermal
evolution of decoupled massive particles. Although the ingredients in our
results have been addressed in Ref.\cite{Weinberg}, the strategies employed
here are simpler, and the results obtained here are more general.Comment: JHEP style, 4 pages, to appear in CQ
The Solar Proton Burning Process Revisited In Chiral Perturbation Theory
The proton burning process p + p -> d + e(+) + \nu(e), important for the
stellar evolution of main-sequence stars of mass equal to or less than that of
the Sun, is computed in effective field theory using chiral perturbation
expansion to the next-to-next-to leading chiral order. This represents a
model-independent calculation consistent with low-energy effective theory of
QCD comparable in accuracy to the radiative np capture at thermal energy
previously calculated by first using very accurate two-nucleon wavefunctions
backed up by an effective field theory technique with a finite cut-off. The
result obtained thereby is found to support within theoretical uncertainties
the previous calculation of the same process by Bahcall and his co-workers.Comment: 30 pages, 2 eps files, aaspp4.sty needed, slightly modified, to be
published in Ap.
Higgs-Flavor Groups, Naturalness, and Dark Matter
In the absence of low-energy supersymmetry, a multiplicity of weak-scale
Higgs doublets would require additional fine-tunings unless they formed an
irreducible multiplet of a non-abelian symmetry. Remnants of such symmetry
typically render some Higgs fields stable, giving several dark matter particles
of various masses. The non-abelian symmetry also typically gives simple,
testable mass relations.Comment: Some comments added after Eqs. (2) and (12
On the Creation of the Universe out of Nothing
We explain how the Universe was created with no expenditure of energy or
initial mass.Comment: To be presented at IWARA 2009 (4th International Workshop on
Astronomy and Relativistic Astrophysics), to be held in Brazil, October 200
Path-Integral Formulation of Pseudo-Hermitian Quantum Mechanics and the Role of the Metric Operator
We provide a careful analysis of the generating functional in the path
integral formulation of pseudo-Hermitian and in particular PT-symmetric quantum
mechanics and show how the metric operator enters the expression for the
generating functional.Comment: Published version, 4 page
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