Physics welcomes the idea that space contains energy whose gravitational effect approximates that of Einstein's cosmological constant, \ensuremath{\Lambda}; today the concept is termed dark energy or quintessence. Physics also suggests that dark energy could be dynamical, allowing for the arguably appealing picture of an evolving dark-energy density approaching its natural value, zero, and small now because the expanding universe is old. This would alleviate the classical problem of the curious energy scale of a millielectron volt associated with a constant \ensuremath{\Lambda}. Dark energy may have been detected by recent cosmological tests. These tests make a good scientific case for the context, in the relativistic Friedmann-Lema\^{\i}tre model, in which the gravitational inverse-square law is applied to the scales of cosmology. We have well-checked evidence that the mean mass density is not much more than one-quarter of the critical Einstein--de Sitter value. The case for detection of dark energy is not yet as convincing but still serious; we await more data, which may be derived from work in progress. Planned observations may detect the evolution of the dark-energy density; a positive result would be a considerable stimulus for attempts at understanding the microphysics of dark energy. This review presents the basic physics and astronomy of the subject, reviews the history of ideas, assesses the state of the observational evidence, and comments on recent developments in the search for a fundamental theory.

/pdf/the-cosmological-constant-and-dark-energy-1w78acsak0.pdf

The Cosmological Constant and Dark Energy

http://cds.cern.ch/record/262851/files/9405029.pdf

Supersymmetry and quantum mechanics

The Hamiltonian H specifies the energy levels and time evolution of a quantum theory. A standard axiom of quantum mechanics requires that H be Hermitian because Hermiticity guarantees that the energy spectrum is real and that time evolution is unitary (probability-preserving). This paper describes an alternative formulation of quantum mechanics in which the mathematical axiom of Hermiticity (transpose +complex conjugate) is replaced by the physically transparent condition of space?time reflection ( ) symmetry. If H has an unbroken symmetry, then the spectrum is real. Examples of -symmetric non-Hermitian quantum-mechanical Hamiltonians are and . Amazingly, the energy levels of these Hamiltonians are all real and positive!Does a -symmetric Hamiltonian H specify a physical quantum theory in which the norms of states are positive and time evolution is unitary? The answer is that if H has an unbroken symmetry, then it has another symmetry represented by a linear operator . In terms of , one can construct a time-independent inner product with a positive-definite norm. Thus, -symmetric Hamiltonians describe a new class of complex quantum theories having positive probabilities and unitary time evolution.The Lee model provides an excellent example of a -symmetric Hamiltonian. The renormalized Lee-model Hamiltonian has a negative-norm 'ghost' state because renormalization causes the Hamiltonian to become non-Hermitian. For the past 50 years there have been many attempts to find a physical interpretation for the ghost, but all such attempts failed. The correct interpretation of the ghost is simply that the non-Hermitian Lee-model Hamiltonian is -symmetric. The operator for the Lee model is calculated exactly and in closed form and the ghost is shown to be a physical state having a positive norm. The ideas of symmetry are illustrated by using many quantum-mechanical and quantum-field-theoretic models.

https://iopscience.iop.org/article/10.1088/0034-4885/70/6/R03/pdf

Making sense of non-Hermitian Hamiltonians

In 1998, Bender and Boettcher found that a wide class of Hamiltonians, even though non-Hermitian, can still exhibit entirely real spectra provided that they obey parity-time requirements or PT symmetry. Here we demonstrate experimentally passive PT-symmetry breaking within the realm of optics. This phase transition leads to a loss induced optical transparency in specially designed pseudo-Hermitian guiding potentials.

Observation of PT-Symmetry Breaking in Complex Optical Potentials

Tables of integrals

GENERAL REMARKS ON SUPERSYMMETRY Background BASIC PRINCIPLES OF SUPERSYMMETRIC QUANTUM MECHANICS SUSY and the Oscillator Problem Superpotential and Setting Up a Supersymmetric Hamiltonian Physical Interpretation of Hs Properties of the Partner Hamiltonians Applications Superspace Formalism Other Schemes of SUSY SUPERSYMMETRIC CLASSICAL MECHANICS Classical Poisson Bracket, Its Generalizations Some Algebraic Properties of the Generalized Poisson Bracket A Classical Supersymmetric Model SUSY Breaking, Witten Index and Index Condition SUSY Breaking Witten Index Finite Temperature SUSY Regulated Witten Index Index Condition q-Deformation and Index Condition Parabosons Deformed Parabose States and Index Condition Witten's Index and Higher-Derivative SUSY Explicit SUSY Breaking and Singular Superpotentials FACTORIZATION METHOD, SHAPE INVARIANCE AND GENERATION OF SOLVABLE PROBLEMS Preliminary Remarks Factorization Method of Infeld and Hull Shape Invariance Condition Self-Similar Potentials A Note on the Generalized Quantum Condition Non-Uniqueness of the Factorizability Phase Equivalent Potentials Generation of Exactly Solvable Potentials in SUSYQM Conditionally Solvable Potentials and SUSY RADIAL PROBLEMS AND SPIN-ORBIT COUPLING SUSY and the Radial Problems Radial Problems Using Ladder Operator Techniques in SUSYQM Isotropic Oscillator and Spin-Orbit Coupling SUSY in D- Dimensions SUPERSYMMETRY IN NONLINEAR SYSTEMS The KdV Equation Conservation Laws in Nonlinear Systems Lax Equations SUSY and Conservation Laws in the KdV - MKdV Systems Darboux's Method SUSY and Conservation Laws in the KdV-SG Systems Supersymmetric KdV Conclusion PARASUPERSYMMETRY Introduction Models of PSUSYQM PSUSY of Arbitrary Order p Truncated Oscillator and PSUSYQM Multidimensional Parasuperalgebras APPENDIX Note: Each chapter also contains a References section

http://inis.jinr.ru/sl/M_Mathematics/MP_Mathematical%20physics/MPs_Symmetry%20and%20groups/Bagchi.%20Supersymmetry%20in%20quantum%20and%20classical%20mechanics%20(CRC,%202001)(226s).pdf

Supersymmetry In Quantum and Classical Mechanics

Known shape-invariant potentials for the constant-mass Schrodinger equation are taken as effective potentials in a position-dependent effective mass (PDEM) one. The corresponding shape-invariance condition turns out to be deformed. Its solvability imposes the form of both the deformed superpotential and the PDEM. A lot of new exactly solvable potentials associated with a PDEM background are generated in this way. A novel and important condition restricting the existence of bound states whenever the PDEM vanishes at an end point of the interval is identified. In some cases, the bound-state spectrum results from a smooth deformation of that of the conventional shape-invariant potential used in the construction. In others, one observes a generation or suppression of bound states, depending on the mass-parameter values. The corresponding wavefunctions are given in terms of some deformed classical orthogonal polynomials.

https://iopscience.iop.org/article/10.1088/0305-4470/38/13/008/pdf

Deformed shape invariance and exactly solvable Hamiltonians with position-dependent effective mass

sl(2, C) as a complex Lie algebra and the associated non-Hermitian Hamiltonians with real eigenvalues

The continuity, equation relating the change in time of the position probability density to the gradient of the probability current density is generalized to PT-symmetric quantum mechanics. The normalization condition of eigenfunctions is modified in accordance with this new conservation law and illustrated with some detailed examples.

Generalized continuity equation and modified normalization in PT-symmetric quantum mechanics

http://cds.cern.ch/record/432937/files/0003277.pdf

Bijan Bagchi

Papers

Supersymmetry In Quantum and Classical Mechanics

Deformed shape invariance and exactly solvable Hamiltonians with position-dependent effective mass

sl(2, C) as a complex Lie algebra and the associated non-Hermitian Hamiltonians with real eigenvalues

Generalized continuity equation and modified normalization in PT-symmetric quantum mechanics

Supersymmetry without hermiticity within PT symmetric quantum mechanics