8 results on '"Mathematical physics"'
Search Results
2. Quadratic approximation for quintessence with arbitrary initial conditions.
- Author
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Swaney, Jeffrey R. and Scherrer, Robert J.
- Subjects
- *
DARK energy , *FORCE & energy , *PHYSICAL cosmology , *SCALAR field theory , *MATHEMATICAL physics - Abstract
We examine quintessence models for dark energy in which the scalar field ɸ evolves near the vicinity of a local maximum or minimum in the potential V(ɸ), so that V(ɸ) can be approximated by a quadratic function of ɸ with no linear term. We generalize previous studies of this type by allowing the initial value of dɸ/dt to be nonzero. We derive an analytic approximation for w(a) and show that it is in excellent agreement with numerical simulations for a variety of scalar field potentials having local minima or maxima. We derive an upper bound on the present-day value of w as a function of the other model parameters and present representative limits on these models from observational data. This work represents a final generalization of previous studies using linear or quadratic approximations for V(ɸ). [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
3. Magnetic field spectrum at cosmological recombination revisited.
- Author
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Shohei Saga, Kiyotomo Ichiki, Keitaro Takahashi, and Naoshi Sugiyama
- Subjects
- *
MAGNETIC fields , *FIELD theory (Physics) , *PERTURBATION theory , *MATHEMATICAL physics , *SCALAR field theory , *RADIATION - Abstract
If vector type perturbations are present in the primordial plasma before recombination, the generation of magnetic fields is known to be inevitable through the Harrison mechanism. In the context of the standard cosmological perturbation theory, nonlinear couplings of first-order scalar perturbations create second-order vector perturbations, which generate magnetic fields. Here we reinvestigate the generation of magnetic fields at second-order in cosmological perturbations on the basis of our previous study, and extend it by newly taking into account the time evolution of purely second-order vector perturbations with a newly developed second-order Boltzmann code. We confirm that the amplitude of magnetic fields from the product-terms of the first-order scalar modes is consistent with the result in our previous study. However, we find, both numerically and analytically, that the magnetic fields from the purely second-order vector perturbations partially cancel out the magnetic fields from one of the product-terms of the first-order scalar modes, in the tight coupling regime in the radiation dominated era. Therefore, the amplitude of the magnetic fields on small scales, k≳10 hMpc-1, is smaller than the previous estimates. The amplitude of the generated magnetic fields at cosmological recombination is about Brec = 5.0×10-24 Gauss on k = 5.0×10-1 hMpc-1. Finally, we discuss the reason for the discrepancies that exist in estimates of the amplitude of magnetic fields among other authors. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
4. Stabilizing the Planck mass shortly after inflation.
- Author
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van de Bruck, Carsten, Christopherson, Adam, and Robinson, Mathew
- Subjects
- *
PLANCK'S energy , *GRAVITATIONAL constant , *FORCE & energy , *SCALAR field theory , *MATHEMATICAL physics , *GRAVITATIONAL interactions , *POWER spectra - Abstract
We consider a model of the early Universe which consists of two scalar fields: the inflaton and a second field which drives the stabilization of the Planck mass (or gravitational constant). We show that the nonminimal coupling of this second field to the Ricci scalar sources a nonadiabatic pressure perturbation. By performing a fully numerical calculation, we find, in turn, that this boosts the amplitude of the primordial power spectrum after inflation. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
5. Rotating Ellis wormholes in four dimensions.
- Author
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Kleihaus, Burkhard and Kunz, Jutta
- Subjects
- *
SCALAR field theory , *ALGEBRAIC field theory , *MATHEMATICAL physics , *WORMHOLES (Physics) , *SPACETIME - Abstract
We present rotating wormhole solutions in general relativity, which are supported by a phantom scalar field. These solutions evolve from the static Ellis wormhole, when the throat is set into rotation. As the rotational velocity increases, the throat deforms until, at a maximal value of the rotational velocity, an extremal Kerr solution is encountered. The rotating wormholes attain a finite mass and quadrupole moment. They exhibit ergospheres and possess bound orbits. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
6. Critical behavior of a nonlocal φ4 field theory and asymptotic freedom
- Author
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Roberto Trinchero
- Subjects
High Energy Physics - Theory ,Scalar field theory ,Ciencias Físicas ,FIELD THEORY ,Física de Partículas y Campos ,01 natural sciences ,Asymptotic freedom ,purl.org/becyt/ford/1 [https] ,Renormalization ,Condensed Matter - Strongly Correlated Electrons ,symbols.namesake ,0103 physical sciences ,Beta function (physics) ,Feynman diagram ,010306 general physics ,CRITICAL PHENOMENA ,Condensed Matter - Statistical Mechanics ,Mathematical physics ,Coupling constant ,Physics ,010308 nuclear & particles physics ,Order (ring theory) ,purl.org/becyt/ford/1.3 [https] ,ASYMPTOTIC FREEDOM ,NON LOCAL ,symbols ,Critical exponent ,CIENCIAS NATURALES Y EXACTAS - Abstract
The critical behaviour of a non-local scalar field theory is studied. This theory has a non-local kinetic term which involves a real power 1-2\alpha of the Laplacian. The interaction term is the usual local \phi^{4} interaction. The lowest order Feynman diagrams corresponding to coupling constant renormalization, mass renormalization and field renormalization are computed. Particular features appearing in the renormalization of these non-local theory that differ from the case of local theories are studied. The previous calculations lead to the perturbative computation of the coupling constant beta function and critical exponents \nu and \eta. In four dimensions for \alpha, Comment: 11 pages, 4 figures, 1 table
- Published
- 2018
7. Positivity bounds for scalar field theories
- Author
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Andrew J. Tolley, Shuang-Yong Zhou, Scott Melville, Claudia de Rham, and Science and Technology Facilities Council (STFC)
- Subjects
Scalar field theory ,DISPERSION RELATIONS ,gr-qc ,Astronomy & Astrophysics ,01 natural sciences ,Upper and lower bounds ,SCATTERING-AMPLITUDES ,Physics, Particles & Fields ,UNITARITY ,0103 physical sciences ,Effective field theory ,010306 general physics ,Mathematical physics ,Physics ,Science & Technology ,Unitarity ,010308 nuclear & particles physics ,hep-th ,hep-ph ,Scattering amplitude ,UV completion ,Physical Sciences ,astro-ph.CO ,Scalar field ,Mass gap ,BEHAVIOR - Abstract
Assuming the existence of a local, analytic, unitary UV completion in a Poincar\'e invariant scalar field theory with a mass gap, we derive an infinite number of positivity requirements using the known properties of the amplitude at and away from the forward scattering limit. These take the form of bounds on combinations of the pole subtracted scattering amplitude and its derivatives. In turn, these positivity requirements act as constraints on the operator coefficients in the low energy effective theory. For certain theories these constraints can be used to place an upper bound on the mass of the next lightest state that must lie beyond the low energy effective theory if such a UV completion is to ever exist.
- Published
- 2017
8. One-loop effective potential in nonlocal scalar field models
- Author
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E. R. Bezerra de Mello, F. Briscese, V. B. Bezerra, A. Yu. Petrov, Briscese, F, E. R., Bezerra de Mello, A. Yu., Petrov, Bezerra, V. B., Briscese, F., De Mello, E. R. B., and Petrov, A. Y.
- Subjects
Physics ,High Energy Physics - Theory ,Nuclear and High Energy Physics ,Scalar field theory ,Perturbation (astronomy) ,FOS: Physical sciences ,Observable ,Cosmological model ,General Relativity and Quantum Cosmology (gr-qc) ,Mathematical Physics (math-ph) ,General Relativity and Quantum Cosmology ,Gravitation ,Quantum nonlocality ,Theoretical physics ,Classical mechanics ,High Energy Physics - Theory (hep-th) ,Scalar field ,Mathematical Physics - Abstract
In this paper we apply the usual perturbative methodology to evaluate the one-loop effective potential in a nonlocal scalar field theory. We find that the effect induced by the nonlocaliity of the theory is always very small and we discuss the consequences of this result. In particular we argue that, looking at one-loop corrections for matter fields, it is not possible to find signals of the nonlocality of the theory in cosmological observables since, even during inflation when energies are very high, nonlocality-induced corrections are expected to be very small.
- Published
- 2015
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