Takahiro Terada, KEK
Bouncing Universe from Nothing
Meeting room 1, Kenkyu honkan 1F We find a class of solutions for a homogeneous and isotropic universe in which the initially expanding universe stops expanding, experiences contraction, and then expands again (the “bounce”), in the framework of Einstein gravity with a real scalar field without violating the null energy condition nor encountering any singularities. Two essential ingredients for the bouncing universe are the positive spatial curvature and the scalar potential which becomes flatter at large field values. Depending on the initial condition, either the positive curvature or the negative potential stops the cosmic expansion and begins the contraction phase. The flat potential plays a crucial role in triggering the bounce. After the bounce, the flat potential naturally allows the universe to enter the slow-roll inflation regime, thereby making the bouncing universe compatible with observations. If the e-folding of the subsequent inflation is just enough, a positive spatial curvature may be found in the future observations. Our scenario nicely fits with the creation of the universe from nothing, which leads to the homogeneous and isotropic universe with positive curvature. As a variant of the mechanism, we also find solutions representing a cyclic universe.
We find a class of solutions for a homogeneous and isotropic universe in which the initially expanding universe stops expanding, experiences contraction, and then expands again (the “bounce”), in the framework of Einstein gravity with a real scalar field without violating the null energy condition nor encountering any singularities. Two essential ingredients for the bouncing universe are the positive spatial curvature and the scalar potential which becomes flatter at large field values. Depending on the initial condition, either the positive curvature or the negative potential stops the cosmic expansion and begins the contraction phase. The flat potential plays a crucial role in triggering the bounce. After the bounce, the flat potential naturally allows the universe to enter the slow-roll inflation regime, thereby making the bouncing universe compatible with observations. If the e-folding of the subsequent inflation is just enough, a positive spatial curvature may be found in the future observations. Our scenario nicely fits with the creation of the universe from nothing, which leads to the homogeneous and isotropic universe with positive curvature. As a variant of the mechanism, we also find solutions representing a cyclic universe.
Reference:
H. Matsui, F. Takahashi and T. Terada, “Bouncing Universe from Nothing,” arXiv:1904.12312 [gr-qc].
Yoshinori Matsuo, Osaka University
Vacuum energy and apparent horizon
Meeting room 1, Kenkyu honkan 1F
Effects of the negative vacuum energy plays a crucial role in a small neighborhood of the apparent horizon of evaporating black holes. We consider spherically symmetric configurations in which the collapsing star has already collapsed below the Schwarzschild radius. For static case, there are no divergences around the Schwarzschild radius even in the Boulware vacuum, if the back reaction from the negative vacuum energy is taken into account. The geometry around the Schwarzschild radius is modified by the effect of vacuum energy and has no event horizon. Instead, there is a local minimum in the radius, like the geometry around the neck of the wormhole. The local minimum of the radius becomes the apparent horizon when the black hole is evaporating by the Hawking radiation. Information can get away from the apparent horizon since it is time-like because of the negative vacuum energy.
Yoshitaka Hatta, Brookhaven National Laboratory
Unraveling the nucleon's mass and spin structure at an Electron-Ion Collider
Seminar room, Kenkyu honkan 3F, slides (kek.jp only)
The US-based Electron-Ion Collider (EIC) is a future high-luminosity, polarized ep and eA collider dedicated to the physics of the nucleon/nucleus structure. I will give a theory overview of the science cases for the EIC. A special emphasis is placed on the partonic origin of the mass and spin of the nucleon, namely, how they can be understood in terms of quarks’ and gluons’ degrees of freedom. I will give a review of the mass and spin decompositions in QCD and discuss possible experimental observables
Masayuki Asakawa, Department of Physics, Graduate School of Science, Osaka University
Toward the understanding of strongly interacting quark-gluon plasma
Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
It was discovered at RHIC that the quark-gluon plasma is very strongly interacting matter contrary to naive expectation. First I will explain how this conclusion was drawn with emphasis on the characteristics of the physics of high energy nuclear collisions. After the introduction, I will examine the interaction in the quark-gluon plasma in three ways: interaction measure, charmonia with finite momenta, and fluctuations of conserved quantities. In the presentation, I will mainly discuss physical implications rather than technical details.
Takeshi Morita, Shizuoka University
Nuclear physics and D-branes in string theory
Meeting room 3, Kenkyu honkan 1F, slides (kek.jp only), slides (kek.jp only)
Holographic QCD predicts that nucleons in QCD may be described by D-branes so called baryon vertices in string theory. The effective theory of the baryon vertices is a matrix quantum mechanics similar to the Dp-Dp+4-brane systems. We study this quantum mechanics and find a similarity with the quark model. By solving our model for small numbers of baryons, we obtain the Gell-Mann-Okubo formula for hyperons, baryon resonances, dibaryon spectra, and a stable Helium like nucleus. In such a way, D-brane dynamics may be understood as nuclear physics.
Masatoshi Yamada, Heidelberg University
Scalegenesis from a bilinear scalar condensate and its phenomenological implications
Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
We consider a classically scale invariant extension of the standard model where non-abelian scalar-gauge theory in a hidden sector is introduced to explain the origin of the electroweak scale. Due to the strong dynamics in the hidden sector a bilinear scalar condensate occurs and becomes an origin of a scale. We discuss phenomenological implications from this extension.
Masatoshi Yamada, Heidelberg U
Introduction to the functional renormalization group
Meeting room 3, Kenkyu honkan 1F
The functional renormalization group is a powerful tool to study critical phenomena in quantum field theory. In this lecture, we introduce its basic ideas and applications to scalar theories in 3 and 4 dimensional spacetime. We discuss the concept of renormalizability and the so-called gauge hierarchy problem from the view point of the functional renormalization group.
Mohab Abou Zeid, University of Gottingen
T-duality in (2,1) superspace and SKT geometry
Seminar room, Kenkyu honkan 3F
I will explain our recent derivation of the T-duality transformation rules for two-dimensional (2,1) supersymmetric sigma-models in (2,1) superspace. To this end I will first review the gauging of sigma-models in (2,1) superspace and present a new manifestly real and geometric expression for the gauged action. I will also discuss the obstructions to gauging (2,1) sigma-models and show that the obstructions to (2,1) T-duality are considerably weaker than the obstructions to gauging. Our complexified T-duality transformations are equivalent to the usual Buscher duality transformations (including an important refinement) together with diffeomorphisms.
So Chigusa, University of Tokyo
Indirect Studies of Electroweakly Interacting Particles at 100 TeV Hadron Colliders
Meeting room 1, Kenkyu honkan 1F
There are many models beyond the standard model which include electroweakly interacting massive particles (EWIMPs), often in the context of the dark matter. We study the indirect search of EWIMPs using a precise measurement of the lepton pair production cross sections at future 100 TeV hadron colliders. It is revealed that this search strategy is suitable in particular for Higgsino and that the Higgsino mass up to about 850 GeV will be covered at 5 sigma level irrespective of the chargino and neutralino mass difference. We also show that the property of the observed signal, in particular its weak charges and mass, can be independently read off by using both the neutral and the charged current processes.
Pablo Soler, Institute for Theoretical Physics, University of Heidelberg
Swampland conjectures and some phenomenological applications
Meeting room 1, Kenkyu honkan 1F
