理論物理学セミナー
127 イベント
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セミナー
Causality Constraints on Black Hole Thermodynamics in Nonlinear Electrodynamics
2026年3月6日(金) 16:00 - 17:30
吉村 果保 (東京大学 大学院総合文化研究科 博士課程)
Black holes exhibit thermodynamic properties and provide an important window into the quantum aspects of gravity. In this context, nonlinear electrodynamics (NLED) offers a useful framework for constructing and analyzing charged black-hole solutions beyond Maxwell theory. Requiring causality - namely, excluding superluminal signal propagation - imposes nontrivial constraints on the allowed form of the NLED Lagrangian. In this talk, we focus on two quantities: the charge-to-mass ratio and the entropy density (entropy-to-mass squared ratio). The charge-to-mass ratio is expected to obey a monotonic behavior consistent with the Weak Gravity Conjecture, while the entropy density is also anticipated to be monotonic, reflecting the expectation that higher-energy effective theories contain more degrees of freedom. We show that these monotonic behaviors follow directly from the causality constraints on the NLED sector.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Non-perturbative geodesic length in JT gravity and universal time evolution of holographic complexity
2026年3月2日(月) 16:00 - 17:00
渋谷 翔之 (名古屋大学 博士課程)
The interplay between black hole interior dynamics and quantum chaos provides a crucial framework for probing quantum effects in quantum gravity. According to the holographic "Complexity=Volume" proposal, we investigated non-perturbative generating function of geodesic length in Jackiw-Teitelboim (JT) gravity to uncover universal signatures of quantum chaos and quantum complexity. We observed that the generating function interpolates between two major probes of quantum chaos - spectral form factor and complexity - highlighting its utility as a probe of chaotic spectrum in quantum gravity. Generalizing the result to general chaotic systems, we demonstrated that time evolution of the complexity is universally governed by a certain pole structure of observables, suggesting a validity of wide class of observables as a probe of quantum chaos in quantum gravity.
会場: via Zoom / セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Noninvertible symmetry protected topological phases on lattice
2026年2月25日(水) 10:30 - 11:30
Weiguang Cao (PD, Centre for Quantum Mathematics, University of Southern Denmark, Denmark)
The recent discovery of noninvertible symmetries—a radical extension of conventional symmetry—has challenged long-standing paradigms in condensed matter physics and quantum information and opened new territory in both theory and technology. Unlike ordinary symmetries, which can be inverted, these symmetries behave like projections (one-way operations) yet still strongly constrain quantum dynamics and enable new classes of phases and phase transitions. However, their role in organizing and stabilizing novel quantum phases remains poorly understood. One important example is a symmetry protected topological (SPT) phase, characterized by nontrivial edge modes and potential applications in quantum information. In this talk, I will discuss the classification of noninvertible symmetry-protected topological (NISPT) phases in both closed and open quantum systems using a duality-based method, and present concrete lattice realizations. These lattice models provide controlled playgrounds in which the physics of noninvertible symmetry can be explored numerically and, potentially, experimentally.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Tunneling with physics-informed renormalisation group flows in the anharmonic oscillator
2026年2月20日(金) 10:00 - 11:00
Friederike Ihssen (Postdoctoral Fellow, Physics, Ruhr University Bochum, Germany)
The resolution of strongly correlated physical systems is computationally hard, but can be simplified enormously by a formulation in terms of suitable dynamical degrees of freedom. Within the functional renormalisation group framework, physics-informed renormalisation group flows (PIRG flows) [1] implement scale-dependent coordinate transformations that can be used to devise optimal expansion schemes around such degrees of freedom. Recently, we have applied PIRG flows to the anharmonic oscillator, with an emphasis on the weak coupling regime with its instanton-dominated tunnelling processes [2]. We show that the instanton physics behind the exponential decay of the energy gap is already covered in the first order of the derivative expansion of the PIRG. The crucial new ingredients in the present analysis are the use of the ground state expansion within PIRG flows, as well as precision numerics based on Galerkin methods. Our result a_inst = 1.910(2) for the decay constant is in quantitative agreement with the analytic one, a_inst = 1.886 with a deviation of 1%. This illustrates very impressively the capacity of the PIRG for fully capturing non-perturbative physics already in relatively simple approximations.
会場: via Zoom / 研究本館
イベント公式言語: 英語
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セミナー
Classical Spinning Black Hole Scattering from Quantum Amplitudes
2026年1月15日(木) 14:00 - 15:30
Dogan Akpinar (Ph.D. Student, Higgs Centre for Theoretical Physics, School of Physics and Astronomy, University of Edinburgh, UK)
Scattering amplitudes have recently become a powerful tool for extracting classical observables in two-body gravitational dynamics, with direct relevance for current and future gravitational-wave experiments. In this talk, I will review how quantum scattering amplitudes can be used to obtain classical black hole scattering observables. A key focus will be the inclusion of spin effects, modelled by treating black holes as point particles in fixed-spin representations. This approach introduces a subtle ambiguity in the separation between classical and quantum information, which we resolve using our spin interpolation method. Leveraging this, we obtain, for the first time, the classical two-loop amplitude accurate to quartic order in spin, from which we extract physical observables such as linear and angular impulses using covariant Dirac brackets. Remarkably, the resulting amplitude obeys a spin-shift symmetry, remaining invariant under a shift of the black hole spin by the momentum transfer in the scattering process. Motivated by this structure, we examine the conserved quantities governing scattering and show that—at least asymptotically—the probe dynamics remain integrable through quartic order in spin. Under this asymptotic integrability, together with the spin-shift symmetry, we demonstrate that the quartic-in-spin radial action is fully determined by the aligned-spin sector. Taken together, these results advance our understanding of spinning black hole scattering and illuminate new structural features of Kerr dynamics.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Cosmological correlators beyond the de-Sitter invariance
2025年12月24日(水) 15:00 - 17:00
Zhu Yuhang (Postdoctoral Researcher, Particle Theory and Cosmology Group, Center for Theoretical Physics of the Universe (CTPU), Institute for Basic Science (IBS), Republic of Korea)
Cosmological correlators serve as powerful probes of the physics that governed the Universe in its earliest moments. Yet analytic calculations of correlators involving massive spinning fields are highly challenging. Recent progress in the cosmological bootstrap program has greatly deepened our understanding of these correlators. In this talk, we will show how to extend the bootstrap program beyond exact de Sitter invariance by studying two types of symmetry breaking: explicit scale-invariance breaking and boost breaking. We will present the boundary differential equations that characterise correlators in these settings and highlight the rich phenomenology that emerges. Finally, we will also show recent developments in approximation methods, based on the combination of exact WKB and saddle-point method, which provide a precise, efficient, and physically transparent way to capture and classify the non-analytic features of correlators.
会場: via Zoom / セミナー室 (359号室)
イベント公式言語: 英語
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セミナー
The Functional Renormalisation Group: From the physics of strongly correlated systems to generative models
2025年12月5日(金) 10:30 - 12:00
Jan Martin Pawlowski (Professor, Institute for Theoretical Physics, University of Heidelberg, Germany)
In the past decades, the functional renormalisation group (fRG) has matured into a comprehensive approach to strongly-correlated (non-perturbative) systems, covering quantitatively both universal and non-universal phenomena. The fRG also constitutes an ideal approach for unravelling structural aspects of quantum field theories. This is not only interesting for studies in mathematical physics, but also guides systematic diagrammatic expansion schemes. It is also used to set up novel statistical (lattice) approaches to non-perturbative phenomena. In the present talk I survey these advances and illustrate the progress with selected examples ranging from ultracold atoms, QCD and quantum gravity to novel generative architectures for lattice simulations and beyond.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Towards the prediction of clusters of primordial black holes
2025年11月7日(金) 16:00 - 17:30
Danilo Artigas (京都大学 大学院理学研究科 物理学・宇宙物理学専攻 物理学第二教室 学振特別研究員PD)
Primordial black holes (PBHs) are a major candidate for dark matter, expected to form from the collapse of large density fluctuations generated during inflation. Their abundance is highly sensitive to non-linear effects, some of which can be described through the δN formalism. This approach models the universe as a set of locally homogeneous patches evolving independently throughout inflation. However, accounting for the spatial correlations between these patches is crucial to predicting the spatial distribution of PBHs and the formation of clusters. In this talk, after reviewing the δN formalism, I will show how to include spatial correlations within this framework. As an illustration, I will discuss the ultra-slow-roll model and compute the curvature perturbation ζ — necessary to determine PBH formation — and its spatial correlations at the end of inflation. In the future, this could enable the prediction of PBH binaries and clusters, which may leave observable imprints such as gravitational waves.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Topological Field Theory Coupled to Parameter Spaces
2025年10月15日(水) 13:30 - 15:00
安藤 貴政 (京都大学 基礎物理学研究所 博士課程)
Topological quantum field theories (TQFTs) describe the IR fixed points of wide classes of gapped theories and are useful for studying many-body quantum phases of matter. In this talk, I will talk about TQFTs coupled to parameter spaces. I first explain the motivation for studying such TQFTs with parameter spaces from two perspectives: generalizing the description of the partition function with background gauge fields, and generalizing to invariants of many-body gapped phases over parameter spaces, known as the Berry phase. Then I will explain how these two are related by showing two physically motivated maps that connect them. The construction of these maps provides physical evidence for the Cobordism Hypothesis. I also discuss other related topics, such as the bulk-boundary correspondence. The talk is based on my ongoing work with Ryan Thorngren (UCLA).
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Quantum tunneling in the curved spacetime
2025年10月2日(木) 13:30 - 15:00
山口 昌英 (Director, Center for Theoretical Physics of the Universe, Institute for Basic Science, Republic of Korea)
False vacuum decay is theorized to have occurred frequently throughout the history of the universe, particularly during first-order phase transitions associated with spontaneous symmetry breaking. The decay rate of such a vacuum is governed by Euclidean bounce solutions, which can exhibit a wide range of configurations, even under fixed boundary conditions. In the absence of gravitational effects, it was established over four decades ago—under reasonable assumptions—that the most symmetric bounce solution, namely the O(4)-symmetric one, minimizes the Euclidean action. This renders it the dominant tunneling path in flat spacetime. However, when gravitational effects are taken into account—as is essential in cosmological settings—all prior studies have assumed, without rigorous proof, that the O(4)-symmetric bounce continues to minimize the action. This has remained a longstanding unresolved problem for more than forty years. In this work, we address this issue by employing the anti-de Sitter/conformal field theory (AdS/CFT) correspondence to determine the configuration with the lowest Euclidean action in a metastable AdS false vacuum. Within the Euclidean formalism of Callan and Coleman, we identify the most probable decay channel of the AdS vacuum. The AdS/CFT duality enables us to sidestep the technical challenges intrinsic to metastable gravitational systems. We demonstrate that the Fubini bounce in conformal field theory—which is dual to the Coleman–de Luccia (CdL) bounce in AdS—indeed minimizes the Euclidean action among all finite bounce solutions in a conformal scalar field theory. Consequently, under certain conditions, we establish that the CdL bounce yields the lowest action among all relevant configurations, including both large and thin-wall limits. Time permitting, we also discuss the prefactor of the decay rate, as obtained from one-loop quantum corrections.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
What constitutes a gravitational wave in an expanding universe?
2025年10月1日(水) 16:00 - 17:30
Yi-Zen Chu (Professor, Department of Physics, National Central University, Taiwan)
Our understanding of gravitational waves produced by isolated astrophysical systems is primarily based on gravitational perturbation theory off a flat spacetime background. This leads to the common identification of gravitational radiation with massless spin-2 waves. In this talk, I will argue that gravitational waves may no longer be solely "spin-2" in character once the background spacetime is our expanding universe instead. As a result of the mixing between gravitational and other degrees of freedom, scalar "spin-0" gravitational waves may exist during the radiation-dominated epoch of our universe; as well as during its current accelerated expansion phase -- provided the main driver is not the cosmological constant, but some extra "Dark Energy" field. Moreover, during the radiation-dominated era, spin-0 Cherenkov gravitational waves may even be generated if its material source were traveling faster than 1/\sqrt{3}.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Spontaneous quasiparticle creation in an analogue preheating experiment
2025年9月30日(火) 10:00 - 12:00
アモリ・ミケリ (理化学研究所 数理創造研究センター (iTHEMS) 数理基礎部門 特別研究員)
Abstract: First, I will briefly outline the motivations and concepts that underpin the analogue gravity program. Next, I will provide a detailed description of a specific experiment designed to simulate various features of the cosmological reheating era. Finally, I will present our recent experimental results from this setup, where we demonstrated the parametric creation of quasiparticle pairs from the quantum vacuum, drawing an analogy with the preheating phase of reheating.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
The QCD phase diagram at finite densities
2025年9月29日(月) 13:30 - 15:00
Franz Sattler (Postdoc, Faculty of Physics, Bielefeld University, Germany)
I discuss recent progress towards calculating the QCD phase diagram at finite density using the functional Renormalisation Group (fRG). After introducing the fRG as applied to QCD, I explain some of the challenges encountered in functional approaches to the QCD phase diagram. Many of these can be resolved by recent developments of new numerical methods. In particular, the application of numerical hydrodynamics to RG flows and resolution of momentum dependences allow us to make progress towards quantitative access to the region of the conjectured critical end-point (CEP) of the QCD phase diagram. An interesting result is the appearance of new phases characterised by spatial modulations (the moat regime) and inhomogeneous condensates at high densities from a self-consistent first-principles calculation. For the near future, a clear program emerges to further pinpoint the CEP and its possibly modified nature using the fRG.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Lecture 2 on "Modular Structures in N=4 supersymmetric Yang-Mills theory"
2025年9月19日(金) 14:30 - 17:30
Daniele Dorigoni (Associate Professor, University of Durham, UK)
In this lecture series we present recent results in the study of exact correlation functions of half-BPS operators in N=4 supersymmetric Yang-Mills theory (SYM) averaged over the space-time insertion points. After presenting some basic properties of 1/2-BPS operators in N=4 SYM, we review how these integrated correlation functions can be obtained from a matrix model formulation of the N=4 path-integral. We then move to present two different integrated correlation functions of four superconformal primary operators of the stress-tensor multiplet which are holographically related to scattering amplitudes of 4-gravitons in type IIB superstring theory on an AdS_5 x S^5 background. We derive exact expressions both in the number of colours N, as well as in the complexified Yang-Mills coupling \tau. A key player in our discussion is electro-magnetic duality of N=4 SYM which provides strong constraints on the coupling dependence of such observables which, in particular, have to be real-analytic modular invariant functions of \tau. We then discuss the large-N fixed-\tau limit to show how these results can be interpreted on the dual stringy side. We also present some details on how these integrated correlator can be used to supplement the standard bootstrap approach leading to exciting coupling dependent bounds on the anomalous dimensions of non-protected operators in N=4 SYM, such as the Konishi operator. Lastly, we discuss an integrated correlation function involving two superconformal primary operators in the stress tensor multiplet in the presence of a half-BPS line defect operator, such as a Wilson line. Electro-magnetic duality is again fundamental in understanding the exact dependence from the coupling constant \tau. [OPTIONAL: If time and energy permit, I can also present some new results regarding integrated correlation functions of two light operators, dual to gravitons on the holographic side, and heavy giant graviton operators, dual to D3 branes extended on the background geometry]
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Lecture 1 on "Modular Structures in N=4 supersymmetric Yang-Mills theory"
2025年9月18日(木) 14:30 - 17:30
Daniele Dorigoni (Associate Professor, University of Durham, UK)
In this lecture series we present recent results in the study of exact correlation functions of half-BPS operators in N=4 supersymmetric Yang-Mills theory (SYM) averaged over the space-time insertion points. After presenting some basic properties of 1/2-BPS operators in N=4 SYM, we review how these integrated correlation functions can be obtained from a matrix model formulation of the N=4 path-integral. We then move to present two different integrated correlation functions of four superconformal primary operators of the stress-tensor multiplet which are holographically related to scattering amplitudes of 4-gravitons in type IIB superstring theory on an AdS_5 x S^5 background. We derive exact expressions both in the number of colours N, as well as in the complexified Yang-Mills coupling \tau. A key player in our discussion is electro-magnetic duality of N=4 SYM which provides strong constraints on the coupling dependence of such observables which, in particular, have to be real-analytic modular invariant functions of \tau. We then discuss the large-N fixed-\tau limit to show how these results can be interpreted on the dual stringy side. We also present some details on how these integrated correlator can be used to supplement the standard bootstrap approach leading to exciting coupling dependent bounds on the anomalous dimensions of non-protected operators in N=4 SYM, such as the Konishi operator. Lastly, we discuss an integrated correlation function involving two superconformal primary operators in the stress tensor multiplet in the presence of a half-BPS line defect operator, such as a Wilson line. Electro-magnetic duality is again fundamental in understanding the exact dependence from the coupling constant \tau. [OPTIONAL: If time and energy permit, I can also present some new results regarding integrated correlation functions of two light operators, dual to gravitons on the holographic side, and heavy giant graviton operators, dual to D3 branes extended on the background geometry]
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Multi-strangeness matter from ab initio calculations
2025年9月16日(火) 13:30 - 15:00
童 辉 (Post-doctoral Fellow, Helmholtz-Institut für Strahlen- und Kernphysik, University of Bonn, Germany)
Hypernuclei and hypernuclear matter connect nuclear structure in the strangeness sector with the astrophysics of neutron stars, where hyperons are expected to emerge at high densities and affect key astrophysical observables. We present the first ab initio calculations that simultaneously describe single- and double- hypernuclei from the light to medium-mass range, the equation of state for -stable hypernuclear matter, and neutron star properties. Despite the formidable complexity of quantum Monte Carlo (QMC) simulations with multiple baryonic degrees of freedom, by combining nuclear lattice effective field theory with a newly developed auxiliary-field QMC algorithm we achieve the first sign-problem free ab initio QMC simulations of hypernuclear systems containing arbitrary number of neutrons, protons, and hyperons, including all relevant two- and three-body interactions. This eliminates reliance on the symmetry-energy approximation, long used to interpolate between symmetric nuclear matter and pure neutron matter. Our unified calculations reproduce hyperon separation energies, yield a neutron star maximum mass consistent with observations, predict tidal deformabilities compatible with gravitational-wave measurements, and give a trace anomaly in line with Bayesian constraints. By bridging the physics of finite hypernuclei and infinite hypernuclear matter within a single ab initio framework, this work establishes a direct microscopic link between hypernuclear structure, dense matter composition, and the astrophysical properties of neutron stars.
会場: セミナー室 (359号室) (メイン会場) / via Zoom
イベント公式言語: 英語
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セミナー
Exciting Possibilities of Multi-Messenger Windows on Cosmic Accelerators
2025年9月9日(火) 13:30 - 15:00
安田 航一朗 (Ph.D. Student, Department of Physics and Astronomy, University of California, Los Angeles, USA)
Active Galactic Nuclei (AGN) jets are among the most extreme particle accelerators in the universe and are thought to play a key role in the origin of ultra-high-energy cosmic rays. Yet, the physical processes inside these jets, particularly those involving heavy nuclei, remain poorly understood. In this talk, I will explore how nuclear and atomic processes in AGN jets can leave distinctive multi-messenger signatures, from neutrino production via nuclear decays to characteristic gamma-ray features from nuclear excitations. These phenomena offer a new window into the microscopic physics of nuclei under astrophysical extreme conditions, while also serving as macroscopic probes of jet composition and acceleration mechanisms. I will also discuss how upcoming observations, including neutrino flavor studies and MeV gamma-ray missions, could provide critical tests of these ideas and shed light on the role of nuclear physics in shaping cosmic accelerators.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Shadow formation in gravitational collapse: redshift and blueshift by spacetime dynamics
2025年8月28日(木) 16:00 - 17:30
古賀 泰敬 (大阪工業大学 情報科学部 情報知能学科 助教)
A black hole illuminated by a background light source is observed as a black hole shadow. For a black hole formed by the gravitational collapse of a transmissive object, redshift of light due to the spacetime dynamics is expected to play a crucial role in the shadow formation. In this talk, we investigate the redshift of light caused by the spacetime dynamics. First, we consider a spherical shell model. We see that the collapse of a shell typically leads to the redshift of light, while blueshift can be also observed in some cases. This result suggests that a shadow image is generally formed in the late stage of the gravitational collapse of a transmissive object. Second, we consider a general, dynamical, spherically symmetric spacetime and propose a new covariant formula for the redshift of light. This formula relates the dynamical redshift to the energy-momentum tensor of the background spacetime and provides its intuitive interpretation with Newtonian analogy.
会場: via Zoom / セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
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セミナー
Analysis of inflationary models in higher-dimensional uniform inflation
2025年8月27日(水) 16:00 - 18:00
廣瀬 拓哉 (九州産業大学 教育研究施設 基礎教育サポートセンター 特任助教)
In this talk, we consider higher-dimensional uniform inflation, in which the extra dimensions expand at the same rate as three-dimensional non- compact space during inflation. We compute the cosmological perturbation in $D+4$ dimensions and derive the spectral index $n_s$ and the tensor- scalar ratio $r$. We analyze five inflationary models: chaotic inflation, natural inflation, quartic hilltop inflation, inflation with spontaneously broken SUSY, and $R^2$ inflation. By combining the results from these models with the Planck 2018 constraints, we discuss that it is not desirable for the extra-dimensional space to expand at the same rate as the three-dimensional non-compact space, except for the case of one extra dimension. This talk is based on arXiv:2501.13581[hep-ph].
会場: セミナー室 (359号室)
イベント公式言語: 英語
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セミナー
Observational constraint of non-scalar phantom dark energies
2025年8月26日(火) 16:00 - 17:30
Hsu-Wen Chiang (Postdoc, Department of Physics, Southern University of Science and Technology, China)
Recent observation of DESI strongly disfavors cosmological constant. Given the lack of constraint regarding the fundamental field that constitutes a dynamical dark energy, people traditionally resort on a hypothetical scalar field. We instead consider minimally coupled non-spinless field as alternative, specifically the extended Proca-Nuevo theory (spin-1) and 3-form field (spin-3). Both theories at the background level permit pure phantom (w < -1) and phantom crossing (w < -1 to w > -1) scenarios. Furthermore, with reasonable choice of EFT parameters we can decouple the scalar perturbation of the dark energy from the matter sector. However, the Lorentz constraint within the higher-spin field inevitably modifies the response of the scalar potential to the matter perturbation. This leads to an enhancement of the matter power spectrum most obvious in BAO fullshape analysis. We then perform MCMC analysis and show that the Hubble tension is alleviated, and the non-spin-0 models are preferred marginally over a cosmological constant.
会場: セミナー室 (359号室) 3階 359号室とZoomのハイブリッド開催
イベント公式言語: 英語
127 イベント