Uses of zeta regularization in QFT with boundary conditions: a cosmo-topological Casimir effect

Zeta regularization has proven to be a powerful and reliable tool for the regularization of the vacuum energy density in ideal situations. With the Hadamard complement, it has been shown to provide finite (and meaningful) answers too in more involved cases, as when imposing physical boundary conditions (BCs) in two-- and higher--dimensional surfaces (being able to mimic, in a very convenient way, other {\it ad hoc} cut-offs, as non-zero depths). What we have considered is the {\it additional} contribution to the cc coming from the non-trivial topology of space or from specific boundary conditions imposed on braneworld models (kind of cosmological Casimir effects). Assuming someone will be able to prove (some day) that the ground value of the cc is zero, as many had suspected until very recently, we will then be left with this incremental value coming from the topology or BCs. We show that this value can have the correct order of magnitude in a number of quite reasonable models involving small and large compactified scales and/or brane BCs, and supergravitons.Comment: 9 pages, 1 figure, Talk given at the Seventh International Workshop Quantum Field Theory under the Influence of External Conditions, QFEXT'05, Barcelona, September 5-9, 200

Topology, Mass and Casimir energy

The vacuum expectation value of the stress energy tensor for a massive scalar field with arbitrary coupling in flat spaces with non-trivial topology is discussed. We calculate the Casimir energy in these spaces employing the recently proposed {\it optical approach} based on closed classical paths. The evaluation of the Casimir energy consists in an expansion in terms of the lengths of these paths. We will show how different paths with corresponding weight factors contribute in the calculation. The optical approach is also used to find the mass and temperature dependence of the Casimir energy in a cavity and it is shown that the massive fields cannot be neglected in high and low temperature regimes. The same approach is applied to twisted as well as spinor fields and the results are compared with those in the literature.Comment: 18 pages, 1 figure, RevTex format, Typos corrected and references adde

On the issue of imposing boundary conditions on quantum fields

An interesting example of the deep interrelation between Physics and Mathematics is obtained when trying to impose mathematical boundary conditions on physical quantum fields. This procedure has recently been re-examined with care. Comments on that and previous analysis are here provided, together with considerations on the results of the purely mathematical zeta-function method, in an attempt at clarifying the issue. Hadamard regularization is invoked in order to fill the gap between the infinities appearing in the QFT renormalized results and the finite values obtained in the literature with other procedures.Comment: 13 pages, no figure

Temperature effect in the Casimir attraction of a thin metal film

The Casimir effect for conductors at arbitrary temperatures is theoretically studied. By using the analytical properties of the Green functions and applying the Abel-Plan formula to Lifshitz's equation, the Casimir force is presented as sum of a temperature dependent and vacuum contributions of the fluctuating electromagnetic field. The general results are applied to the system consisting of a bulk conductor and a thin metal film. It is shown that a characteristic frequency of the thermal fluctuations in this system is proportional to the square root of a thickness of the metal film. For the case of the sufficiently high temperatures when the thermal fluctuations play the main role in the Casimir interaction, this leads to the growth of the effective dielectric permittivity of the film and to a disappearance of the dependence of Casimir's force on the sample thickness.Comment: LaTeX 2.09, 8 pages, no figure

Hamiltonian approach to the dynamical Casimir effect

A Hamiltonian approach is introduced in order to address some severe problems associated with the physical description of the dynamical Casimir effect at all times. For simplicity, the case of a neutral scalar field in a one-dimensional cavity with partially transmitting mirrors (an essential proviso) is considered, but the method can be extended to fields of any kind and higher dimensions. The motional force calculated in our approach contains a reactive term --proportional to the mirrors' acceleration-- which is fundamental in order to obtain (quasi)particles with a positive energy all the time during the movement of the mirrors --while always satisfying the energy conservation law. Comparisons with other approaches and a careful analysis of the interrelations among the different results previously obtained in the literature are carried out.Comment: 4 pages, no figures; version published in Phys. Rev. Lett. 97 (2006) 13040

Dynamical Casimir Effect with Semi-Transparent Mirrors, and Cosmology

After reviewing some essential features of the Casimir effect and, specifically, of its regularization by zeta function and Hadamard methods, we consider the dynamical Casimir effect (or Fulling-Davis theory), where related regularization problems appear, with a view to an experimental verification of this theory. We finish with a discussion of the possible contribution of vacuum fluctuations to dark energy, in a Casimir like fashion, that might involve the dynamical version.Comment: 11 pages, Talk given in the Workshop ``Quantum Field Theory under the Influence of External Conditions (QFEXT07)'', Leipzig (Germany), September 17 - 21, 200

Gauge Dependence of the Effective Average Action in Einstein Gravity

We study the gauge dependence of the effective average action Gamma_k and Newtonian gravitational constant using the RG equation for Gamma_k. Then we truncate the space of action functionals to get a solution of this equation. We solve the truncated evolution equation for the Einstein gravity in the De Sitter background for a general gauge parameter alpha and obtain a system of equations for the cosmological and the Newtonian constants. Analyzing the running of the gravitational constant we find that the Newtonian constant depends strongly on the gauge parameter. This leads to the appearance of antiscreening and screening behavior of the quantum gravity. The resolution of the gauge dependence problem is suggested. For physical gauges like the Landau-De Witt gauge the Newtonian constant shows an antiscreening.Comment: 19 pages, LaTeX, 1 figure, misprints correcte

Nursing Virtual Reality Training Program for SBIRT (Screening, Brief Intervention and Referral to Treatment)

Can a virtual reality training simulator enhance a nurse's ability to learn basic screening, brief intervention, and referral to treatment (SBIRT) skills better than traditional training programs? Based on SBIRT’s universal screening process, it was determined that the most beneficial training application would be one that created role playing simulations wherein practitioners could test their skills and knowledge within an immersive environment. The portability and accessibility provided by this virtual reality application not only addresses the limited opportunities students must practice screening and brief intervention skills, but also presents a practical solution to conducting tests while keeping physical distancing measures in place. As today’s world faces the need for strict social distancing measures, technologies like virtual reality open doors to practice a new way of interaction and learning. Past studies have researched whether standard online video training modules, in-person instruction, role-plays and optional patient simulations have a sufficient effect in student practitioner’s overall performance; however, simulated training in virtual reality was not considered as part of the equation. Our research will be focused on the efficacy of our virtual reality training simulator on a student’s acquisition and retention of the relevant learning material. We will do this by measuring the amount of exposure that is needed before significant changes are observed in a practitioner’s SBIRT knowledge, skills, and confidence when compared to other traditional programs. By utilizing text-to-speech solutions, user audio input, and lip-synced animation on virtual avatars, we can create a realistic environment that nurses can use to practice and test their SBIRT skills. With a variety of scenarios, voices, and characters, the application “Nursing Virtual Reality SBIRT Training Program” will provide a variety of simulated environments for training and education in healthcare