48,349 research outputs found
The Kovacs effect in the one-dimensional Ising model: a linear response analysis
We analyze the so-called Kovacs effect in the one-dimensional Ising model
with Glauber dynamics. We consider small enough temperature jumps, for which a
linear response theory has been recently derived. Within this theory, the
Kovacs hump is directly related to the monotonic relaxation function of the
energy. The analytical results are compared with extensive Monte Carlo
simulations, and an excellent agreement is found. Remarkably, the position of
the maximum in the Kovacs hump depends on the fact that the true asymptotic
behavior of the relaxation function is different from the stretched exponential
describing the relevant part of the relaxation at low temperatures.Comment: accepted for publication in Phys. Rev.
Two charges on plane in a magnetic field I. "Quasi-equal" charges and neutral quantum system at rest cases
Low-lying bound states for the problem of two Coulomb charges of finite
masses on a plane subject to a constant magnetic field perpendicular to the
plane are considered. Major emphasis is given to two systems: two charges with
the equal charge-to-mass ratio (quasi-equal charges) and neutral systems with
concrete results for the Hydrogen atom and two electrons (quantum dot). It is
shown that for these two cases, but when a neutral system is at rest (the
center-of-mass momentum is zero), some outstanding properties occur: in double
polar coordinates in CMS and relative coordinate
systems (i) the eigenfunctions are factorizable, all factors except for
-dependent are found analytically, they have definite relative angular
momentum, (ii) dynamics in -direction is the same for both systems being
described by a funnel-type potential; (iii) at some discrete values of
dimensionless magnetic fields the system becomes {\it
quasi-exactly-solvable} and a finite number of eigenfunctions in are
polynomials. The variational method is employed. Trial functions are based on
combining for the phase of a wavefunction (a) the WKB expansion at large
distances, (b) the perturbation theory at small distances (c) with a form of
the known analytically (quasi-exactly-solvable) eigenfunctions. For the lowest
states with relative magnetic quantum numbers this approximation
gives not less than 7 s.d., 8 s.d., 9 s.d., respectively, for the total energy
for magnetic fields
(Hydrogen atom) and (two electrons).Comment: 38 pages, 8 figures, 11 table
Two charges on plane in a magnetic field: II. Moving neutral quantum system across a magnetic field
The moving neutral system of two Coulomb charges on a plane subject to a
constant magnetic field perpendicular to the plane is considered. It is
shown that the composite system of finite total mass is bound for any
center-of-mass momentum and magnetic field strength; the energy of the
ground state is calculated accurately using a variational approach. Their
accuracy is cross-checked in a Lagrange-mesh method for a.u. and in a
perturbation theory at small and . The constructed trial function has
the property of being a uniform approximation of the exact eigenfunction. For a
Hydrogen atom and a Positronium a double perturbation theory in and is
developed and the first corrections are found algebraically. A phenomenon of a
sharp change of energy behavior for a certain center-of-mass momentum and a
fixed magnetic field is indicated.Comment: 24 pages, 5 figures, 13 tables (6 in main body and 7 moved in a
supplementary material), several clarifying sentences and 3 extra references
added, Chapter II rectified, typos fixed, Annals of Physics (to be published
Conformal Laplace superintegrable systems in 2D: polynomial invariant subspaces
2nd-order conformal superintegrable systems in dimensions are Laplace
equations on a manifold with an added scalar potential and independent
2nd order conformal symmetry operators. They encode all the information about
Helmholtz (eigenvalue) superintegrable systems in an efficient manner: there is
a 1-1 correspondence between Laplace superintegrable systems and Stackel
equivalence classes of Helmholtz superintegrable systems. In this paper we
focus on superintegrable systems in two dimensions, , where there are 44
Helmholtz systems, corresponding to 12 Laplace systems. For each Laplace
equation we determine the possible 2-variate polynomial subspaces that are
invariant under the action of the Laplace operator, thus leading to families of
polynomial eigenfunctions. We also study the behavior of the polynomial
invariant subspaces under a Stackel transform. The principal new results are
the details of the polynomial variables and the conditions on parameters of the
potential corresponding to polynomial solutions. The hidden gl_3-algebraic
structure is exhibited for the exact and quasi-exact systems. For physically
meaningful solutions, the orthogonality properties and normalizability of the
polynomials are presented as well. Finally, for all Helmholtz superintegrable
solvable systems we give a unified construction of 1D and 2D quasi-exactly
solvable potentials possessing polynomial solutions, and a construction of new
2D PT-symmetric potentials is established.Comment: 28 page
Three-loop Correction to the Instanton Density. II. The Sine-Gordon potential
In this second paper on quantum fluctuations near the classical instanton
configurations, see {\em Phys. Rev. D \bf 92}, 025046 (2015) and
arXiv:1501.03993, we focus on another well studied quantum-mechanical problem,
the one-dimensional Sine-Gordon potential (the Mathieu potential). Using only
the tools from quantum field theory, the Feynman diagrams in the instanton
background, we calculate the tunneling amplitude (the instanton density) to the
three-loop order. The result confirms (to seven significant figures) the one
recently recalculated by G. V. Dunne and M. \"{U}nsal, {\it Phys. Rev. \bf D
89}, 105009 (2014) from the resurgence perspective. As in the double well
potential case, we found that the largest contribution is given by the diagrams
originating from the Jacobian. We again observe that in the three-loop case
individual Feynman diagrams contain irrational contributions, while their sum
does not.Comment: 14 pages, 3 figures, 1 table, already published at Phys.Rev.D: a post
published version with tadpole diagrams redrawn to mark clearly the Jacobian
source, Note Added about significance of a tadpole diagram in 3-,4-,5-loops
contribution
Fluctuations in quantum mechanics and field theories from a new version of semiclassical theory. II
This is the second paper on semiclassical approach based on the density
matrix given by the Euclidean time path integral with fixed coinciding
endpoints. The classical path, interpolating between this point and the
classical vacuum, called "flucton", plus systematic one- and two-loop
corrections, has been calculated in the first paper \cite{Escobar-Ruiz:2016aqv}
for double-well potential and now extended for a number of quantum-mechanical
problems (anharmonic oscillator, sine-Gordon potential). The method is based on
systematic expansion in Feynman diagrams and thus can be extended to QFTs. We
show that the loop expansion in QM reminds the leading log-approximations in
QFT. In this sequel we present complete set of results obtained using this
method in unified way. Alternatively, starting from the Schr\"{o}dinger
equation we derive a {\it generalized} Bloch equation which semiclassical-like,
iterative solution generates the loop expansion. We re-derive two loop
expansions for all three above potentials and now extend it to three loops,
which has not yet been done via Feynman diagrams. All results for both methods
are fully consistent with each other. Asymmetric (tilted) double-well potential
(non-degenerate minima) is also studied using the second method
Studying the Triple Higgs Self-Coupling Via e+e- --> b bar b HH, t bar t HH at Future Linear e+e- Colliders
We study the triple Higgs self-coupling at future colliders
energies, with the reactions and . We evaluate the total cross section of , and
calculate the total number of events considering the complete set of Feynman
diagrams at tree-level. The sensitivity of the triple Higgs coupling is
considered in the Higgs mass range 110-190 , for the energy which is
expected to be available at a possible Next Linear Collider with a
center-of-mass energy and luminosity 1000 .Comment: 15 pages, 10 figure
Neutral Higgs Boson Pair-Production and Trilinear Self-Couplings in the MSSM at ILC and CLIC Energies
We study pair-production as well as the triple self-couplings of the neutral
Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM) at the Future
International Linear Collider (ILC) and Compact Linear Collider
(CLIC). The analysis is based on the reactions with . We evaluate the total cross-section for
both , and calculate the total number of events
considering the complete set of Feynman diagrams at tree-level. We vary the
triple couplings , ,
, , and
within the range and +2. The numerical
computation is done for the energies expected at the ILC with a center-of-mass
energy 500, 1000, 1600 and a luminosity 1000 . The channels
and are also
discussed to a center-of-mass energy of 3 and luminosities of 1000
and 5000 .Comment: 26 pages, 11 figure
Chaotic Dynamics of Comet 1P/Halley; Lyapunov Exponent and Survival Time Expectancy
The orbital elements of comet Halley are known to a very high precision,
suggesting that the calculation of its future dynamical evolution is
straightforward. In this paper we seek to characterize the chaotic nature of
the present day orbit of comet Halley and to quantify the timescale over which
its motion can be predicted confidently. In addition, we attempt to determine
the timescale over which its present day orbit will remain stable. Numerical
simulations of the dynamics of test particles in orbits similar to that of
comet Halley are carried out with the Mercury 6.2 code. On the basis of these
we construct survival time maps to assess the absolute stability of Halley's
orbit, frequency analysis maps, to study the variability of the orbit and we
calculate the Lyapunov exponent for the orbit for variations in initial
conditions at the level of the present day uncertainties in our knowledge of
its orbital parameters. On the basis of our calculations of the Lyapunov
exponent for comet Halley, the chaotic nature of its motion is demonstrated.
The e-folding timescale for the divergence of initially very similar orbits is
approximately 70 years. The sensitivity of the dynamics on initial conditions
is also evident in the self-similarity character of the survival time and
frequency analysis maps in the vicinity of Halley's orbit, which indicates
that, on average, it is unstable on a timescale of hundreds of thousands of
years. The chaotic nature of Halley's present day orbit implies that a precise
determination of its motion, at the level of the present day observational
uncertainty, is difficult to predict on a timescale of approximately 100 years.
Furthermore, we also find that the ejection of Halley from the solar system or
its collision with another body could occur on a timescale as short as 10,000
years.Comment: 11 pages, 10 figures, accepted for publication in MNRA
Three-loop Correction to the Instanton Density. I. The Quartic Double Well Potential
This paper deals with quantum fluctuations near the classical instanton
configuration. Feynman diagrams in the instanton background are used for the
calculation of the tunneling amplitude (the instanton density) in the
three-loop order for quartic double-well potential. The result for the
three-loop contribution coincides in six significant figures with one given
long ago by J.~Zinn-Justin. Unlike the two-loop contribution where all involved
Feynman integrals are rational numbers, in the three-loop case Feynman diagrams
can contain irrational contributions.Comment: 15 pages, 3 figures, 1 table, already published at Phys.Rev.D92
(2015) 025046, 089902(erratum), a post published version with tadpole
diagrams redrawn to clearly mark the Jacobian source and misprint on 3-loop
tadpole contribution on p.8 fixe
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