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Ralf Schützhold

Publications and source records attributed to Ralf Schützhold.

140 records · Page 8Linked to original sources
arXiv2004

A relativistic toy model for back-reaction

We consider a quantized massless and minimally coupled scalar field on a circular closed string with a time-dependent radius $R(t)$, whose undisturbed dynamics is governed by the Nambu-Goto action. Within the semi-classical treatment, the back-reaction of the quantum field onto the string dynamics is taken into account in terms of the renormalized expectation value of the energy-momentum tensor including the trace anomaly. The results indicate that the back-reaction could prevent the collapse of the circle $R\downarrow0$ -- however, the semi-classical picture fails to describe the string dynamics at the turning point (i.e., possible bounce) at finite values of $R$ and $\dot R$. The fate of the closed string after that point (e.g., oscillation or eternal acceleration) cannot be determined within the semi-classical picture and thus probably requires the full quantum treatment. PACS: 04.62.+v, 03.70.+k, 11.15.Kc, 04.60.-m.

gr-qc↗
arXiv2004

Resonant cavity photon creation via the dynamical Casimir effect

Motivated by a recent proposal for an experimental verification of the dynamical Casimir effect, the macroscopic electromagnetic field within a perfect cavity containing a thin slab with a time-dependent dielectric permittivity is quantized in terms of the dual potentials. For the resonance case, the number of photons created out of the vacuum due to the dynamical Casimir effect is calculated for both polarizations (TE and TM). PACS: 42.50.Lc, 03.70.+k, 42.50.Dv, 42.60.Da.

quant-ph↗
arXiv2002

Pattern recognition on a quantum computer

By means of a simple example it is demonstrated that the task of finding and identifying certain patterns in an otherwise (macroscopically) unstructured picture (data set) can be accomplished efficiently by a quantum computer. Employing the powerful tool of the quantum Fourier transform the proposed quantum algorithm exhibits an exponential speed-up in comparison with its classical counterpart. The digital representation also results in a significantly higher accuracy than the method of optical filtering. PACS: 03.67.Lx, 03.67.-a, 42.30.Sy, 89.70.+c.

quant-ph↗
arXiv2002

Gravity wave analogs of black holes

It is demonstrated that gravity waves of a flowing fluid in a shallow basin can be used to simulate phenomena around black holes in the laboratory. Since the speed of the gravity waves as well as their high-wavenumber dispersion (subluminal vs. superluminal) can be adjusted easily by varying the height of the fluid (and its surface tension) this scenario has certain advantages over the sonic and dielectric black hole analogs, for example, although its use in testing quantum effects is dubious. It can be used to investigate the various classical instabilities associated with black (and white) holes experimentally, including positive and negative norm mode mixing at horizons. PACS: 04.70.-s, 47.90.+a, 92.60.Dj, 04.80.-y.

gr-qc↗
arXiv2002

Dynamical Casimir Effect in a Designed Leaky Cavity

The phenomenon of particle creation within a resonantly vibrating lossy cavity is investigated for the example of a massless scalar field at finite temperature. Leakage is provided by insertion of a dispersive mirror into a larger ideal cavity. Via the rotating wave approximation we demonstrate that for the case of parametric resonance the exponential growth of the number of created particles and the strong enhancement at finite temperatures are preserved in the presence of reasonable losses. The relevance for experimental tests of quantum radiation via the dynamical Casimir effect is addressed.

quant-ph↗
arXiv2002

A cosmological constant from the QCD trace anomaly?

According to recent astrophysical observations the large scale mean pressure of our present universe is negative suggesting a positive cosmological constant like term. This article addresses the question of whether non-perturbative effects of self-interacting quantum fields in curved space-times may yield a significant contribution. Focusing on the trace anomaly of quantum chromo-dynamics (QCD), a preliminary estimate of the expected order of magnitude yields a remarkable coincidence with the empirical data, indicating the potential relevance of this effect. PACS: 04.62.+v, 12.38.Aw, 12.38.Lg, 98.80.Es.

gr-qc↗
arXiv2001

Quantum radiation at finite temperature

We investigate the phenomenon of quantum radiation - i.e. the conversion of (virtual) quantum fluctuations into (real) particles induced by dynamical external conditions - for an initial thermal equilibrium state. For a resonantly vibrating cavity a rather strong enhancement of the number of generated particles (the dynamical Casimir effect) at finite temperatures is observed. Furthermore we derive the temperature corrections to the energy radiated by a single moving mirror and an oscillating bubble within a dielectric medium as well as the number of created particles within the Friedmann-Robertson-Walker universe. Possible implications and the relevance for experimental tests are addressed. PACS: 42.50.Lc, 03.70.+k, 11.10.Ef, 11.10.Wx.

quant-ph↗
arXiv2001

Nonuniqueness of the $λΦ^4$-vacuum

We prove that the massless neutral $λΦ^4$-theory does not possess a unique vacuum. Based on the Wightman axioms the non-existence of a state which preserves Poincar{é} and scale invariance is demonstrated non-perturbatively for a non-vanishing self-interaction. We conclude that it is necessary to break the scale invariance in order to define a vacuum state. The renormalized vacuum expectation value of the energy-momentum tensor is derived from the two-point Wightman function employing the point-splitting technique and its relation to the phionic and the scalar condensate is addressed. Possible implications to other self-interacting field theories and to different approaches in quantum field theory are pointed out. PACS: 11.10.Cd, 11.15.Tk, 11.30.Qc

hep-th↗
arXiv2001

Dielectric black hole analogues

Alternative to the sonic black hole analogues we discuss a different scenario for modeling the Schwarzschild geometry in a laboratory - the dielectric black hole. The dielectric analogue of the horizon occurs if the velocity of the medium with a finite permittivity exceeds the speed of light in that medium. The relevance for experimental tests of the Hawking effect and possible implications are addressed. PACS: 04.70.Dy, 04.62.+v, 04.80.-y, 42.50.Gy.

quant-ph↗
arXiv2001

On the Hawking effect

In terms of the Painlev{é}-Gullstrand-Lema{\^ı}tre coordinates a rather general scenario for the gravitational collapse of an object and the subsequent formation of a horizon is described by a manifestly $C^\infty$-metric. For a 1+1 dimensional model of the collapse the leading contributions to the Bogoliubov coefficients are calculated explicitely and the Hawking temperature is recovered. But depending on the particular dynamics of the collapse the final state represents either evaporation or anti-evaporation. The generalization of the calculation to 3+1 dimensions is outlined and possible implications are addressed. PACS-numbers: 04.70.Dy, 04.70.-s, 04.62.+v.

gr-qc↗
arXiv2000

On the anomalous dimension for the transversity distribution

We show that a standard calculation of the splitting function for the nonsinglet structure function h_1 does not lead to the expected result. The calculation is compared to the corresponding derivation of the splitting function for the nonsinglet polarized structure function g_1. We analyze possible explanations for the unexpected result and discuss its implications. PACS: 11.10.Hi; 11.40.-q; 11.55.Ds; 13.88.+e

hep-ph↗
arXiv2000

On the Particle Definition in the presence of Black Holes

A canonical particle definition via the diagonalisation of the Hamiltonian for a quantum field theory in specific curved space-times is presented. Within the provided approach radial ingoing or outgoing Minkowski particles do not exist. An application of this formalism to the Rindler metric recovers the well-known Unruh effect. For the situation of a black hole the Hamiltonian splits up into two independent parts accounting for the interior and the exterior domain, respectively. It turns out that a reasonable particle definition may be accomplished for the outside region only. The Hamiltonian of the field inside the black hole is unbounded from above and below and hence possesses no ground state. The corresponding equation of motion displays a linear global instability. Possible consequences of this instability are discussed and its relations to the sonic analogues of black holes are addressed. PACS-numbers: 04.70.Dy, 04.62.+v, 10.10.Ef, 03.65.Db.

gr-qc↗
arXiv1998

Quantum radiation in external background fields

A canonical formalism is presented which allows for investigations of quantum radiation induced by localized, smooth disturbances of classical background fields by means of a perturbation theory approach. For massless, non-selfinteracting quantum fields at zero temperature we demonstrate that the low-energy part of the spectrum of created particles exhibits a non-thermal character. Applied to QED in varying dielectrics the response theory approach facilitates to study two distinct processes contributing to the production of photons: the squeezing effect due to space-time varying properties of the medium and of the velocity effect due to its motion. The generalization of this approach to finite temperatures as well as the relation to sonoluminescence is indicated.

quant-ph↗