scholarly journals Minimal surfaces and generalized Einstein–Maxwell-dilaton theory

2019 ◽  
Vol 34 (12) ◽  
pp. 1950061
Author(s):  
M. Butler ◽  
A. M. Ghezelbash
Keyword(s):  
Cosmological Constant ◽  
Physical Properties ◽  
Minimal Surfaces ◽  
Higher Dimensions ◽  
Coupling Constants ◽  
Dilaton Field ◽  
Coupling Constant ◽  
Maxwell Theory ◽  
Five Dimensions ◽  
Cosmological Solutions

We present novel classes of nonstationary solutions to the five-dimensional generalized Einstein–Maxwell-dilaton theory with cosmological constant, in which the Maxwell’s field and the cosmological constant couple to the dilaton field. In the first class of solutions, the two nonzero coupling constants are different, while in the second class of solutions, the two coupling constants are equal to each other. We find consistent cosmological solutions with positive, negative or zero cosmological constant, where the cosmological constant depends on the value of one coupling constant in the theory. Moreover, we discuss the physical properties of the five-dimensional solutions and the uniqueness of the solutions in five dimensions by showing the solutions with different coupling constants cannot be uplifted to any Einstein–Maxwell theory in higher dimensions.

scholarly journals The entropy sum of (A)dS black holes in four and higher dimensions

2014 ◽  
Vol 29 (30) ◽  
pp. 1450172 ◽  
Author(s):  
Wei Xu ◽  
Jia Wang ◽  
Xin-He Meng
Keyword(s):  
Black Holes ◽  
Angular Momentum ◽  
Cosmological Constant ◽  
Higher Dimensions ◽  
Coupling Constant ◽  
Bonnet Gravity ◽  
Charged Black Holes ◽  
Higher Dimensional ◽  
Six Dimensions ◽  
Odd Dimensions

We present the "entropy sum" relation of (A)dS charged black holes in higher-dimensional Einstein–Maxwell gravity, f(R) gravity, Gauss–Bonnet gravity and gauged supergravity. For their "entropy sum" with the necessary effect of the unphysical "virtual" horizon included, we conclude the general results that the cosmological constant dependence and Gauss–Bonnet coupling constant dependence do hold in both the four and six dimensions, while the "entropy sum" is always vanishing in odd dimensions. Furthermore, the "entropy sum" of all horizons is related to the geometry of the horizons in four and six dimensions. In these explicitly four cases, one also finds that the conserved charges M (the mass), Q (the charge from Maxwell field or supergravity) and the parameter a (the angular momentum) play no role in the "entropy sum" relations.

LOW ENERGY QUANTUM GRAVITY, THE COSMOLOGICAL CONSTANT AND GAUGE COUPLING CONSTANTS

2008 ◽  
Vol 17 (13n14) ◽  
pp. 2447-2451
Author(s):  
DAVID J. TOMS
Keyword(s):  
Fixed Point ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
Gauge Coupling ◽  
Low Energy ◽  
Coupling Constants ◽  
Maxwell Theory ◽  
Original Calculation ◽  
Energy Quantum

Robinson and Wilczek have suggested that loop corrections in quantum gravity can alter the running gauge coupling constants from the behaviour found in the absence of gravity. Although their original calculation is not correct, the basic idea behind their paper has been re-examined recently for quantized Einstein–Maxwell theory with a cosmological constant. In this essay I discuss some of the issues surrounding the calculation and mention some of the implications. I argue that it is possible for a theory that is not conventionally asymptotically free to become so in the presence of gravity, and for gravity to lead to a new ultraviolet fixed point. This establishes a provocative link between the microscopic and macroscopic realms.

scholarly journals New class of exact solutions to Einstein–Maxwell-dilaton theory on four-dimensional Bianchi type IX geometry

2021 ◽  
Vol 81 (7) ◽  
Author(s):  
Bardia H. Fahim ◽  
Masoud Ghezelbash
Keyword(s):  
Cosmological Constant ◽  
Bianchi Type ◽  
Cosmological Solution ◽  
Constant Term ◽  
Coupling Constants ◽  
Type Ii ◽  
Dilaton Field ◽  
New Class ◽  
Zero Values ◽  
Special Case

AbstractWe construct new classes of cosmological solution to the five dimensional Einstein–Maxwell-dilaton theory, that are non-stationary and almost conformally regular everywhere. The base geometry for the solutions is the four-dimensional Bianchi type IX geometry. In the theory, the dilaton field is coupled to the electromagnetic field and the cosmological constant term, with two different coupling constants. We consider all possible solutions with different values of the coupling constants, where the cosmological constant takes any positive, negative or zero values. In the ansatzes for the metric, dilaton and electromagnetic fields, we consider dependence on time and two spatial directions. We also consider a special case of the Bianchi type IX geometry, in which the geometry reduces to that of Eguchi–Hanson type II geometry and find a more general solution to the theory.

Assessing the Calculation of Exchange Coupling Constants and Spin Crossover Gaps Using the Approximate Projection Model to Improve Density Function Calculations

2019 ◽  
Author(s):  
Xianghai Sheng ◽  
Lee Thompson ◽  
Hrant Hratchian
Keyword(s):  
Density Functional Theory ◽  
Exchange Coupling ◽  
Density Functional ◽  
Spin Crossover ◽  
Coupling Constants ◽  
Spin Projection ◽  
Coupling Constant ◽  
Projection Model ◽  
Functional Theory

This work evaluates the quality of exchange coupling constant and spin crossover gap calculations using density functional theory corrected by the Approximate Projection model. Results show that improvements using the Approximate Projection model range from modest to significant. This study demonstrates that, at least for the class of systems examined here, spin-projection generally improves the quality of density functional theory calculations of J-coupling constants and spin crossover gaps. Furthermore, it is shown that spin-projection can be important for both geometry optimization and energy evaluations. The Approximate Project model provides an affordable and practical approach for effectively correcting spin-contamination errors in molecular exchange coupling constant and spin crossover gap calculations.

An estimate of the spin–spin coupling constant, 1J(1H,13C), in gaseous benzene

1996 ◽  
Vol 74 (8) ◽  
pp. 1524-1525 ◽  
Author(s):  
Ted Schaefer ◽  
Guy M. Bernard ◽  
Frank E. Hruska
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Dielectric Constant ◽  
Magnetic Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Spin Coupling Constant ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Gaseous Benzene

An excellent linear correlation (r = 0.9999) exists between the spin–spin coupling constants 1J(1H,13C), in benzene dissolved in four solvents (R. Laatikainen et al. J. Am. Chem. Soc. 117, 11006 (1995)) and Ando's solvation dielectric function, ε/(ε – 1). The solvents are cyclohexane, carbon disulfide, pyridine, and acetone. 1J(1H,13C)for gaseous benzene is predicted to be 156.99(2) Hz at 300 K. Key words: spin–spin coupling constants, 1J(1H,13C) for benzene in the vapor phase; spin–spin coupling constants, solvent dielectric constant dependence of 1J(1H,13C) in benzene; benzene, estimate of 1J(1H,13C) in the vapor; nuclear magnetic resonance, estimate of 1J(1H,13C) in gaseous benzene.

Internal motion in benzylidene diacetate and its 2,6-dibromo derivative by DNMR and the J method

1989 ◽  
Vol 67 (6) ◽  
pp. 1022-1026 ◽  
Author(s):  
Ted Schaefer ◽  
Craig S. Takeguchi
Keyword(s):  
Double Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Maximum Magnitude ◽  
Coupling Constant ◽  
Spectral Parameters ◽  
Proton Proton ◽  
Ether Solution ◽  
Spin Spin Coupling ◽  
Dibromo Derivative

The 1H nuclear magnetic resonance spectral parameters are reported for benzylidene diacetate in CS2 and acetone-d6 solutions. The long-range spin–spin coupling constant over six formal bonds, 6J, is used to derive apparent twofold barriers to rotation about the exocyclic C(1)—C bond in the two solutions. The conformation of lowest energy has the α. C—H bond in the benzene plane. The barrier is higher in CS2 than in acetone-d6 solution, in contrast to a molecule like benzyl chloride. In the 2,6-dibromo derivative, the free energy of activation for reorientation about the bond in question is 36 kJ/mol at 165 K in dimethyl ether solution. Such a high barrier implies a very small six-bond proton–proton coupling constant for this derivative because 6J is proportional to the expectation value of sin2θ. The angle θ is zero when the α C—H bond lies in the benzene plane. 6J is −0.051 Hz in acetone-d6 solutions; its sign is determined by double resonance experiments. The question of an angle-independent component of 6J, that is, whether 6J is finite at θ = 0°, is addressed. A maximum magnitude of 0.02 Hz may be present at θ = 0° for the 2,6-dibromo derivative, although a zero magnitude is also compatible with the experimental data. In a compound with a higher internal barrier, α,α,2,6-tetrachlorotoluene, the experimental results are best in accord with a negligibly small 6J at θ = 0°. Keywords: 1H NMR of benzylidene diacetate, spin–spin coupling constants for benzylidene diacetate, DNMR, 2,6-dibromobenzylidene diacetate.

scholarly journals SUPERCONDUCTING PHASE TRANSITION IN THE NAMBU–JONA-LASINIO MODEL

2001 ◽  
Vol 16 (17) ◽  
pp. 1129-1138 ◽  
Author(s):  
M. SADZIKOWSKI
Keyword(s):  
Phase Transition ◽  
Phase Diagram ◽  
Phase Transitions ◽  
Superconducting Phase ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Rich Phase ◽  
Quark Interaction ◽  
Quark Coupling ◽  
Superconducting Phase Transition

The Nambu–Bogoliubov–de Gennes method is applied to the problem of superconducting QCD. The effective quark–quark interaction is described within the framework of the Nambu–Jona-Lasinio model. The details of the phase diagram are given as a function of the strength of the quark–quark coupling constant G′. It is found that there is no superconducting phase transition when one uses the relation between the coupling constants G′ and G of the Nambu–Jona-Lasinio model which follows from the Fierz transformation. However, for other values of G′ one can find a rich phase structure containing both the chiral and the superconducting phase transitions.

KALUZA–KLEIN BOTTLE COUPLED TO TOLMAN–HAWKING WORMHOLE

1991 ◽  
Vol 06 (17) ◽  
pp. 1547-1552
Author(s):  
A. DAVIDSON ◽  
Y. VERBIN
Keyword(s):  
Scalar Field ◽  
Klein Bottle ◽  
Gauge Coupling ◽  
Coupling Constants ◽  
Five Dimensions ◽  
Symmetric Configuration ◽  
Kaluza Klein

Asymptotically Euclidean regions connected by a wormhole may differ by their associated gauge coupling constants. This idea is realized in a field-theoretical manner using a conformally coupled scalar field in five dimensions. An SO (4) × U (1) e.m. -symmetric configuration is derived, describing a Kaluza–Klein bottle coupled to a Tolman–Hawking wormhole.

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