Quantum Particle Creation Research Articles

Mining the quantum vacuum: quantum tunnelling and particle creation

Particle production from the vacuum is a remarkable aspect of particle physics. Prime examples are the Schwinger process of particle production in strong electric fields and the Hawking process of particle production from black holes. These processes can be viewed as quantum tunnelling of particles from the vacuum. The tunnelling approach, and the closely related instanton or complex path approaches, are reviewed here with emphasis on paths in the complex coordinate plane. The method is applied to particle production from a black hole in a magnetic field, where ultra-high energy charged particles are produced.

Radiative gravastar with Gibbons-Hawking temperature

We study the quantum particle creation in a toy model of spherically symmetric gravitational collapse whose final product is not a black hole but a gravastar. Precedent studies revealed that even in the case of the gravitational collapse to form a horizonless ultra-compact object, thermal radiation named transient Hawking radiation is generated at the late stage of the gravitational collapse, and a sudden stop of collapsing motion to form a horizonless ultra-compact object causes one or two bursts of quantum particle creation. The very different behavior of the model studied in this paper from the precedent ones is quantum radiation with a thermal spectrum from the gravastar between two bursts. The temperature of the radiation is not the same as the Hawking one determined by the gravitational mass of the system but the Gibbons-Hawking one of the de Sitter core inside the gravastar.

Upon the horizon’s verge: Thermal particle creation between and approaching horizons

Quantum particle creation from spacetime horizons, or accelerating boundaries in the dynamical Casimir effect, can have an equilibrium, or thermal, distribution. Using an accelerating boundary in flat spacetime (moving mirror), we investigate the production of thermal energy flux despite non-equilibrium accelerations, the evolution between equilibrium states, and the ‘interference’ between horizons. In particular, this allows us to give a complete solution to the particle spectrum of the accelerated boundary correspondence with Schwarzschild–de Sitter spacetime.

Robustness of particle creation in the formation of a compact object

Abstract Hawking predicted that the formation of a black hole by gravitational collapse causes quantum particle creation and the spectrum of the particles is almost thermal. This phenomenon is called Hawking radiation. Recently, it has been predicted that particle creation may drastically change from Hawking radiation to a strong double burst if the gravitational collapse suddenly stops just before the formation of the event horizon. In contrast with Hawking radiation, the burst may be so strong that it can be of observational interest even for collapsing objects with astrophysical mass scales. However, the burst phenomenon has been predicted through studies of idealized models in which a spherical hollow shell begins to collapse, but stops shrinking and eventually settles down to a static “star”. Therefore, one might guess that it could be particular to the hollow shell model. In this paper, we study particle creation due to the gravitational collapse of a spherical object whose interior is filled with matter. In this model, we obtain similar results to those in the case of the hollow shell model. This implies that the double burst is a robust property of particle creation by the sudden braking of gravitational collapse.

Quantum Inequalities and Particle Creation in the Presence of an External, Time-Dependent Mamaev-Trunov Potential

In 2011, Mr. Dan Solomon proposed a model of a quantized scalar field interacting with a time-dependent Mamaev-Trunov potential in two-dimensional Minkowski spacetime. This model is governed by the Klein-Gordon wave equation with a time-dependent potential. Mr. Solomon claims that this model violates both the classical energy conditions of special relativity and the quantum energy conditions of quantum field theory in curved spacetime. Every classical energy condition can be violated, and their natural replacements are known as quantum inequalities. Mr. Solomon attempted to prove violations of the spatial and temporal quantum inequalities, and he correctly assumed that the negative energy splits into two fluxes at the Cauchy surface, where the potential is turned off. Unfortunately, Solomon neglects the contribution to the energy density due to particle creation when the potential is turned off at time t = 0. In this project, we calculate the contribution to the stress energy tensor due to particle creation. We show that while the classical energy conditions are violated, the quantum energy inequalities hold, contrary to Mr. Solomon’s statements.

Quantum Riemannian geometry and particle creation on the integer line

We construct noncommutative or ‘quantum’ Riemannian geometry on the integers as a lattice line with its natural 2-dimensional differential structure and metric given by arbitrary non-zero edge square-lengths . We find for general metrics a unique -preserving quantum Levi-Civita connection, which is flat if and only if ai are a geometric progression where the ratios are constant. More generally, we compute the Ricci tensor for the natural antisymmetric lift of the volume 2-form and find that the quantum Einstein–Hilbert action up to a total divergence is where is the standard discrete Laplacian. We take a first look at some issues for quantum gravity on the lattice line. We also examine 1 + 0 dimensional scalar quantum theory with mass m and the lattice line as discrete time. As an application, we compute discrete time cosmological particle creation for a step function jump in the metric by a factor , finding that an initial vacuum state has at later times an occupancy in the continuum limit, independently of the frequency. The continuum limit of the model is the time-dependent harmonic oscillator, now viewed geometrically.

On the Electric-Magnetic Duality Symmetry: Quantum Anomaly, Optical Helicity, and Particle Creation

It is well known that not every symmetry of a classical field theory is also a symmetry of its quantum version. When this occurs, we speak of quantum anomalies. The existence of anomalies imply that some classical Noether charges are no longer conserved in the quantum theory. In this paper, we discuss a new example for quantum electromagnetic fields propagating in the presence of gravity. We argue that the symmetry under electric-magnetic duality rotations of the source-free Maxwell action is anomalous in curved spacetimes. The classical Noether charge associated with these transformations accounts for the net circular polarization or the optical helicity of the electromagnetic field. Therefore, our results describe the way the spacetime curvature changes the helicity of photons and opens the possibility of extracting information from strong gravitational fields through the observation of the polarization of photons. We also argue that the physical consequences of this anomaly can be understood in terms of the asymmetric quantum creation of photons by the gravitational field.

Weak cosmic censorship, superradiance, and quantum particle creation

Since 1970's, gedanken experiments have been devised to challenge the weak cosmic censorship conjecture (WCCC), which is the expectation that spacetime singularities will be hidden from faraway observers by event horizons so that classical predictability in a spacetime is preserved. These experiments involve the interaction of an extremal or a slightly sub-extremal black hole with a test particle or field, attempting to destroy the horizon, i.e. to create a so-called naked singularity. They usually conclude that WCCC cannot be violated starting from an extremal black hole, but may be violated starting from a slightly sub-extremal one, if backreaction and self-force effects are neglected. Some other works also analyze these effects. Starting 2007, a string of papers argue if WCCC can be violated by classically forbidden interactions occuring via the quantum nature of the particles associated with the fields; and where backrection and/or superradiance are pointed out as effects working in the direction of preserving the WCCC. We correct/modify a backrection argument, and furthermore point out that superradiance does not prevent {\em single particles} from being captured by the black hole; even if this capture would lead to WCCC violation. Then we consider the spontaneous emission (which we call the Zel'dovich-Unruh effect) of particles by the black hole, and find that at least for scalars, it can be understood without second quantization. It also completely invalidates the mentioned single- or few-particle thought experiments. However, the conclusions of our previous work on (at least) scalar fields interacting with black holes, i.e. that WCCC may be violated starting from slightly subextremal black holes, remains valid in this (semi)classical framework.

Twin paradox with macroscopic clocks in superconducting circuits

We propose an implementation of a twin paradox scenario in superconducting circuits, with velocities as large as a few percent of the speed of light. Ultrafast modulation of the boundary conditions for the electromagnetic field in a microwave cavity simulates a clock moving at relativistic speeds. Since our cavity has a finite length, the setup allows us to investigate the role of clock size as well as interesting quantum effects on time dilation. In particular, our theoretical results show that the time dilation increases for larger cavity lengths and is shifted due to quantum particle creation.

CCDM model from quantum particle creation: constraints on dark matter mass

In this work the results from the quantum process of matter creation have been used in order to constrain the mass of the dark matter particles in an accelerated Cold Dark Matter model (Creation Cold Dark Matter, CCDM). In order to take into account a back reaction effect due to the particle creation phenomenon, it has been assumed a small deviation ε for the scale factor in the matter dominated era of the form t2/3+ε. Based on recent H(z) data, the best fit values for the mass of dark matter created particles and the ε parameter have been found as m = 1.6× 103 GeV, restricted to a 68.3% c.l. interval of 1.5 < m < 6.3× 107) GeV and ε = -0.250+0.15-0.096 at 68.3% c.l. For these best fit values the model correctly recovers a transition from decelerated to accelerated expansion and admits a positive creation rate near the present era. Contrary to recent works in CCDM models where the creation rate was phenomenologically derived, here we have used a quantum mechanical result for the creation rate of real massive scalar particles, given a self consistent justification for the physical process. This method also indicates a possible solution to the so called ``dark degeneracy'', where one can not distinguish if it is the quantum vacuum contribution or quantum particle creation which accelerates the Universe expansion.

Expanding cosmology with back reaction term caused by quantum particle creation

An extended Standard cosmological Model is considered with a time dependent cosmological term of the form λ0( ˙ R/dt)/R, R(t) the cosmic scale factor. Such term, that is proportional to the number of quantum particles created by Universe expansion, is introduced to take into account the back reaction to particle creation. The model is first studied when the equation of state p = wρ holds between the energy density ρ and pressure p of the Universe. Exact solutions are determined in the flat space-time case for arbitrary w. The curved space-time cases are solved for w = −1, −1/3. The solutions show the existence of a large variety of possible dynamics of the Universe. The model is studied also when the energy density has the sufficiently general form ρ = ρ0(R/R0) −α . Solutions are given by quadrature. In the flat spacetime case case the quadrature is performed exactly. This shows the existence of an inflationary big-bang at time t = 0 and an accelerated expansion for large t with corresponding particle production. Moreover a numerical determination of the particle creation parameter Ωcr is obtained. In the matter dominated case the value of Ωcr is near to the value of ΩΛ while in the radiation dominated case Ωcr is near to ΩΛ+ΩC where ΩΛ, ΩC are the numerical values of the experimental dark energy and cold dark matter parameters at present time. The model is solved also for ρ =0 ,p � 0. For such unusual situation the value of the ”radius of the Universe” at the present time is calculated

A Cosmological Model of Thermodynamic Open Universe

In this paper we have given a generalisation of the earlier work by Prigogine et al. who have constructed a phenomenological model of entropy production via particle creation in the very early universe generated out of the vacuum rather than from a singularity, by including radiation also as the energy source and tried to develop an alternative cosmological model in which particle creation prevents the big bang. We developed Radiation dominated model of the universe which shows a general tendency that (i) it originates from instability of vacuum rather than from a singularity. (ii) Up to a characteristic time cosmological quantities like density, pressure, Hubble constant and expansion parameter vary rapidly with time. (iii) After the characteristic time these quantities settles down and the models are turned into de-sitter type model with uniform matter, radiation, creation densities and Hubble's constant H. The de-sitter regime survives during a decay time then connects continuously to a usual adiabatic matter radiation RW universe.The interesting thing in the paper is that we have related the phenomenological radiation dominated model to macroscopic model of quantum particle creation in the early universe giving rise to the present observed value of cosmic background radiation . It is also found that the dust filled model tallies exactly with that of the Prigogine's one, which justifies that our model is generalized Prigogine's model. Although the model originates from instability of vacuum rather than from a singularity, still there is a couple of unavoidable singularities in the model.

Naked singularity explosion in higher dimensions

Motivated by the recent argument that in the TeV-scale gravity trans-Planckian domains of spacetime as effective naked singularities would be generated by high-energy particle (and black-hole) collisions, we investigate the quantum particle creation by naked-singularity formation in general dimensions. Background spacetime is simply modeled by the self-similar Vaidya solution, describing the spherical collapse of a null dust fluid. In a generic case the emission power is found to be proportional to the quadratic inverse of the remaining time to a Cauchy horizon, as known in four dimensions. On the other hand, the power is proportional to the quartic inverse for a critical case in which the Cauchy horizon is `degenerate'. According to these results, we argue that the backreaction of the particle creation to gravity will be important in particle collisions, in contrast to the gravitational collapse of massive stellar objects, since the bulk of energy is carried away by the quantum radiation even if a quantum gravitational effect cutoff the radiation just before the appearance of naked singularity.

Particle creation in (2+1) circular dust collapse

We investigate the quantum particle creation during the circularly symmetric collapse of a $2+1$ dust cloud, for the cases when the cosmological constant is either zero or negative. We derive the Ford-Parker formula for the $2+1$ case, which can be used to compute the radiated quantum flux in the geometric optics approximation. It is shown that no particles are created when the collapse ends in a naked singularity, unlike in the $3+1$ case. When the collapse ends in a Banados-Teitelboim-Zanelli black hole, we recover the expected Hawking radiation.

Quantum Effect and Curvature Strength of Naked Singularities

There are many solutions to the Einstein field equations that demonstrate naked singularity (NS) formation after regular evolution. It is possible, however, that such a quantum effect as particle creation prevents NSs from forming. We investigate the relation between the curvature strength and the quantum effects of NSs in a very wide class of spherical dust collapse. Through a perturbative calculation, we find that if the NS is very strong, the quantum particle creation diverges as the Cauchy horizon is approached, while if the NS is very weak, the creation should be finite. In the context of cosmic censorship, strong NSs will be subjected to the backreaction of quantum effects and may disappear or be hidden behind horizons, while weak NSs will not.

Tachyonic Dark Matter

Recent attempts to explain the dark matter and energy content of the universe have involved some radical extensions of standard physics, including quintessence, phantom energy, additional space dimensions, and variations in the speed of light. In this paper I consider the possibility that some dark matter might be in the form of tachyons. I show that, subject to some reasonable assumptions, a tachyonic cosmological fluid would produce distinctive effects, such as a surge in quantum vacuum energy and particle creation, and a change in the conventional temperature–time relation for the normal cosmological material. Possible observational consequences are discussed.

Physical Processes in Naked Singularity Formation

Gravitational collapse is one of the most fruitful subjects in gravitational physics. It is well known that singularity formation is inevitable in complete gravitational collapse. It was conjectured that such a singularity should be hidden by horizons if it is formed from generic initial data with physically reasonable matter fields. Many possible counterexamples to this conjecture have been proposed over the past three decades, although none of them has proved to be sufficiently generic. In these examples, there appears a singularity that is not hidden by horizons. This singularity is called a `naked singularity.' The appearance of a naked singularity represents the formation of an observable high-curvature, strong-gravity region. In this paper we review examples of naked singularity formation and recent progress in research of observable physical processes - gravitational radiation and quantum particle creation - from a forming naked singularity.

Covariant and locally Lorentz-invariant varying speed of light theories

We propose definitions for covariance and local Lorentz invariance applicable when the speed of light $c$ is allowed to vary. They have the merit of retaining only those aspects of the usual definitions which are invariant under unit transformations, and which can therefore legitimately represent the outcome of an experiment. We then discuss some possibilities for invariant actions governing the dynamics of such theories. We consider first the classical action for matter fields and the effects of a changing $c$ upon quantization. We discover a peculiar form of quantum particle creation due to a varying $c$. We then study actions governing the dynamics of gravitation and the speed of light. We find the free, empty-space, no-gravity solution, to be interpreted as the counterpart of Minkowksi space-time, and highlight its similarities with Fock-Lorentz space-time. We also find flat-space string-type solutions, in which near the string core $c$ is much higher. We label them fast-tracks and compare them with gravitational wormholes. We finally discuss general features of cosmological and black hole solutions, and digress on the meaning of singularities in these theories.

Gamma-Ray Bursts and Quantum Cosmic Censorship

Gamma-ray bursts are believed to result from the coalescence of binary neutron stars. However, the standard proposals for conversion of the gravitational energy to thermal energy have difficulties. We show that if the merger of the two neutron stars results in a naked singularity, instead of a black hole, the ensuing quantum particle creation can provide the requisite thermal energy in a straightforward way. The back-reaction of the created particles can avoid the formation of the naked singularity predicted by the classical theory. Hence cosmic censorship holds in the quantum theory, even if it were to be violated in classical general relativity.

Coherent scalar-field oscillations in an expanding universe

Motivated by the cosmological importance of coherent (classical), scalar-field oscillations in the context of the invisible axion and the new inflationary-universe scenario, we analyze, in general, the classical evolution of a scalar field in an isotropic and homogeneous cosmology. For a scalar potential of the form $V(\ensuremath{\varphi})=a{\ensuremath{\varphi}}^{n}$, the energy density of the scalar-field oscillations decreases as ${R}^{\ensuremath{-}\frac{6n}{(n+2)}}$ when the oscillations are rapid compared to the expansion rate ($R=\mathrm{cosmic}\mathrm{scale}\mathrm{factor}$). We also investigate the effect of higher-order terms in the potential perturbatively, and analyze the decay of the coherent field oscillations due to quantum particle creation.