Cutkosky rules and unitarity (violation) in D-instanton amplitudes

In perturbative amplitudes in quantum field theory and string field theory, Cutkosky rule expresses the anti-hermitian part of a Feynman diagram in terms of sum over all its cut diagrams, and this in turn is used to prove unitarity of the theory. For D-instanton contribution to a string theory amplitude, the cutting rule needed for the proof of unitarity is somewhat different; we need to sum over only those cut diagrams for which all the world-sheet boundaries ending on some particular D-instanton lie on the same side of the cut. By working with the closed string effective action, obtained after integrating out the open string modes, we prove that the D-instanton amplitudes actually satisfy these cutting rules, provided the effective action is real. The violation of unitarity in the closed string sector of two dimensional string theory can be traced to the failure of this reality condition. In the critical superstring theory, multi-instanton and multi anti-instanton amplitudes satisfy the reality condition. Contribution to the amplitudes from the instanton anti-instanton sector satisfies the reality condition if we make a specific choice of integration cycle over the configuration space of string fields, whereas contribution due to the non-BPS D-instantons will need to either vanish or have an overall real normalization in order for it to give real contribution. We use Picard-Lefschetz theory to argue that these conditions are indeed satisfied in superstring theories.

COVID and the Era of Emergencies

The threat of emergency measures introduced in face of COVID-19 has largely been framed in terms of individual rights. We argue that it is not the protection of the sovereign individual that is most at stake, but the relations between political subjects and the institutions that enable their robust political participation. Drawing on Hannah Arendt’s analysis of the ways in which isolation and the incapacity to discern truth or reality condition totalitarianism and are exacerbated by it, we argue that the dangers for the evacuation of democratic politics are stark in our era. We consider contemporary political action in concert in Germany to illustrate this critique of COVID-19 emergency measures. Drawing on the legal concept of “appropriateness,” we explicate how the German critical response to the shutdown is founded on a concern for democratic principles and institutions, and aims to achieve two crucial goals: governmental transparency and social-political solidarity.

Vacua and exact solutions in lower-D limits of EGB

We consider the action principles that are the lower dimensional limits of the Einstein–Gauss–Bonnet gravity via the Kaluza–Klein route. We study the vacua and obtain some exact solutions. We find that the reality condition of the theories may select one vacuum over the other from the two vacua that typically arise in Einstein–Gauss–Bonnet gravity. We obtain exact black hole and cosmological solutions carrying scalar hair, including scalar hairy BTZ black holes with both mass and angular momentum turned on. We also discuss the holographic central charges in the asymptotic AdS backgrounds.

Physiological State and Learning Ability of Students in Normal and Virtual Reality Conditions: Complexity-Based Analysis

Background Education and learning are the most important goals of all universities. For this purpose, lecturers use various tools to grab the attention of students and improve their learning ability. Virtual reality refers to the subjective sensory experience of being immersed in a computer-mediated world, and has recently been implemented in learning environments. Objective The aim of this study was to analyze the effect of a virtual reality condition on students’ learning ability and physiological state. Methods Students were shown 6 sets of videos (3 videos in a two-dimensional condition and 3 videos in a three-dimensional condition), and their learning ability was analyzed based on a subsequent questionnaire. In addition, we analyzed the reaction of the brain and facial muscles of the students during both the two-dimensional and three-dimensional viewing conditions and used fractal theory to investigate their attention to the videos. Results The learning ability of students was increased in the three-dimensional condition compared to that in the two-dimensional condition. In addition, analysis of physiological signals showed that students paid more attention to the three-dimensional videos. Conclusions A virtual reality condition has a greater effect on enhancing the learning ability of students. The analytical approach of this study can be further extended to evaluate other physiological signals of subjects in a virtual reality condition.

Physiological State and Learning Ability of Students in Normal and Virtual Reality Conditions: Complexity-Based Analysis (Preprint)

BACKGROUND Education and learning are the most important goals of all universities. For this purpose, lecturers use various tools to grab the attention of students and improve their learning ability. Virtual reality refers to the subjective sensory experience of being immersed in a computer-mediated world, and has recently been implemented in learning environments. OBJECTIVE The aim of this study was to analyze the effect of a virtual reality condition on students’ learning ability and physiological state. METHODS Students were shown 6 sets of videos (3 videos in a two-dimensional condition and 3 videos in a three-dimensional condition), and their learning ability was analyzed based on a subsequent questionnaire. In addition, we analyzed the reaction of the brain and facial muscles of the students during both the two-dimensional and three-dimensional viewing conditions and used fractal theory to investigate their attention to the videos. RESULTS The learning ability of students was increased in the three-dimensional condition compared to that in the two-dimensional condition. In addition, analysis of physiological signals showed that students paid more attention to the three-dimensional videos. CONCLUSIONS A virtual reality condition has a greater effect on enhancing the learning ability of students. The analytical approach of this study can be further extended to evaluate other physiological signals of subjects in a virtual reality condition.

Gaming in Virtual Reality: What Changes in Terms of Usability, Emotional Response and Sense of Presence Compared to Non-Immersive Video Games?

Background. Virtual reality can provide innovative gaming experiences for present and future game players. However, scientific knowledge is still limited about differences between player’s experience in video games played in immersive modalities and games played in non-immersive modalities (i.e., on a desktop display). Materials and method. Smash Hit was played by 24 young adults in immersive (virtual reality) and non-immersive (desktop) condition. Self-report questionnaires (VAS-A, VAS-HP, VAS-SP, SUS, SUS-II) and psycho-physiological measures (heart rate and skin conductance) were used to assess usability, emotional response and the reported sense of presence. Results. No statistical differences emerged between the immersive and the non-immersive condition regarding usability and performance scores. The general linear model for repeated measures conducted on VAS-A, VAS-HP, VAS-SP scores for the virtual reality condition supported the idea that playing in the immersive display modality was associated with higher self-reported happiness and surprise; analysis on SUS-II revealed that the perceived sense of presence was higher in the virtual reality condition Discussion and conclusion. The proposed study provides evidence that (a) playing a video game in virtual reality was not more difficult than playing through a desktop display; (b) players showed a more intense emotional response, as assessed by self-report questionnaires and with psycho-physiological indexes (heart rate and skin conductance), after playing in virtual reality versus after playing through the desktop display; (c) the perceived sense of presence was found to be greater in virtual reality as opposed to the non-immersive condition.

BPS Equations of Monopole and Dyon in SU(2) Yang-Mills-Higgs Model, Nakamula-Shiraishi Models, and Their Generalized Versions from the BPS Lagrangian Method

We apply the BPS Lagrangian method to derive BPS equations of monopole and dyon in the SU2 Yang-Mills-Higgs model, Nakamula-Shiraishi models, and their generalized versions. We argue that, by identifying the effective fields of scalar field, f, and of time-component gauge field, j, explicitly by j=βf with β being a real constant, the usual BPS equations for dyon can be obtained naturally. We validate this identification by showing that both Euler-Lagrange equations for f and j are identical in the BPS limit. The value of β is bounded to β<1 due to reality condition on the resulting BPS equations. In the Born-Infeld type of actions, namely, Nakamula-Shiraishi models and their generalized versions, we find a new feature that, by adding infinitesimally the energy density up to a constant 4b2, with b being the Born-Infeld parameter, it might turn monopole (dyon) to antimonopole (antidyon) and vice versa. In all generalized versions there are additional constraint equations that relate the scalar-dependent couplings of scalar and of gauge kinetic terms or G and w, respectively. For monopole the constraint equation is G=w-1, while for dyon it is wG-β2w=1-β2 which further gives lower bound to G as such G≥2β1-β2. We also write down the complete square-forms of all effective Lagrangians.