Multidimensional Gravity Research Articles

Plasmon-graviton conversion in a magnetic field in TeV-scale gravity

Kaluza-Klein (KK) gravitons emission rates due to plasmon-graviton conversion in magnetic field are computed within the ADD model of TeV-scale gravity. Plasma is described in the kinetic approach as the system of charged particles and Maxwell field both confined on the brane. Interaction with multidimensional gravity living in the bulk with $n$ compact extra dimensions is introduced within the linearized theory. Plasma collective effects enter through the two-point correlation function of the fluctuations of the energy-momentum tensor. The estimate for magnetic stars is presented leading to the lower limit of the D-dimensional Plank mass.

Plasma gravi-bremsstrahlung in TeV-scale gravity

We develop a theory of interaction of a classical plasma with Kaluza-Klein (KK) gravitons in the ADD model of TeV-scale gravity. The plasma is described in the kinetic approach as a system of charged particles and the Maxwell field, both confined to the brane. Interaction with multidimensional gravity living in the bulk with n compact extra dimensions is introduced within a linearized theory. The KK graviton emission rates are computed taking into account plasma collective effects through two-point correlation functions of fluctuations of the plasma energy-momentum tensor. Apart from known mechanisms (such as bremsstrahlung and the gravi-Primakoff effect), we find essentially collective channels such as coalescence of plasma waves into gravitons which may be manifest in turbulent plasmas. Our results indicate that the commonly used KK gravitons production rates in stars and supernovae may be underestimated.

Plasma graviton production in TeV-scale gravity

We develop the theory of interaction of classical plasma with Kaluza-Klein (KK) gravitons in the ADD model of TeV-scale gravity. Plasma is described within the kinetic approach as the system of charged particles and Maxwell field both confined on the brane. Interaction with multidimensional gravity living in the bulk with n compact extra dimensions is introduced within the linearized theory. The KK gravitons emission rates are computed taking into account plasma collective effects through the two-point correlation functions of the fluctuations of the plasma energy-momentum tensor. Apart from known mechanisms (such as bremsstrahlung and gravi-Primakoff effect) we find essentially collective channels such as the coalescence of plasma waves into gravitons which may be manifest in turbulent plasmas. Our results indicate that commonly used rates of the KK gravitons production in stars and supernovae may be underestimated.

Multidimensional world, inflation, and modern acceleration

Starting from pure multidimensional gravity with curvature-nonlinear terms but no matter fields in the initial action, we obtain a cosmological model with two effective scalar fields related to the size of two extra factor spaces. The model includes both an early inflationary stage and that of modern accelerated expansion and satisfies the observational data. There are no small parameters; the effective inflaton mass depends on the initial conditions which explain its small value as compared to the Planck mass. At the modern stage, the size of extra dimensions slowly increases, therefore this model predicts drastic changes in the physical laws of our Universe in the remote future.

Non-relativistic limit of multidimensional gravity: exact solutions and applications

We found the exact solution of the Poisson equation for the multidimensional space with topology . This solution describes the smooth transition from the newtonian behavior 1/r3 for distances bigger than periods of tori (the extra dimension sizes) to multidimensional behavior 1/r1 + d3 + d in the opposite limit. In the case of one extra dimension d = 1, the gravitational potential is expressed via compact and elegant formulae. These exact solutions are applied to some practical problems to get the gravitational potentials for considered configurations. Found potentials are used to calculate the acceleration for point masses and gravitational self-energy. Models with test masses smeared over some (or all) extra dimensions are proposed. In ten-dimensional spacetime with three smeared extra dimensions, it is shown that the size of three rest extra dimensions can be enlarged up to a submillimeter for the case of 1 TeV fundamental Planck scale MPl(10). In the models where all extra dimensions are smeared, the gravitational potential exactly coincides with the newtonian one regardless of the size of the extra dimensions. Nevertheless, the hierarchy problem can be solved in these models.

MULTIDIMENSIONAL COSMOLOGY AND FUNDAMENTAL CONSTANTS

Studies of multidimensional models with different sources (models with S -branes, thin and thick brane worlds, Kaluza-Klein type models in curvature-nonlinear multidimensional gravity etc.) and their application to the cosmological constant, cosmological singularity, hierarchy and coincidence problems are presented. Their observational predictions: variations of fundamental physical constants, new types of black holes and wormholes are discussed.

High-order multidimensional gravity and inflation

Starting from pure multidimensional gravity with higher-order curvature invariants but without any scalar and matter fields, we obtain an inflationary model satisfying the observational data regarding the CMB properties.

The Planck mass as a function of extra space volume

It is shown that, in the framework of multidimensional gravity, the Planck mass depends on the geometry of a compact extra space.

Cosmologies from nonlinear multidimensional gravity with acceleration and slowly varying G

We consider multidimensional gravity with a Lagrangian containing the Ricci tensor squared and the Kretschmann invariant. In a Kaluza-Klein approach with a single compact extra space of arbitrary dimension, with the aid of a slow-change approximation (as compared with the Planck scale), we build a class of spatially flat cosmological models in which both the observed scale factor a(τ) and the extradimensional one, b(τ), grow exponentially at large times, but b(τ) grows slowly enough to admit variations of the effective gravitational constant G within observational limits. Such models predict a drastic change in the physical laws of our Universe in the remote future due to further growth of the extra dimensions.

On a possible test of multidimensional gravity with the aid of neutrons

We consider a possible experimental test of Newton’s law of gravity at small distances with the aid of neutron scattering. A deviation from Newton’s law can be expected if the idea of multidimensional gravity is correct. In the framework of a theoretical model related to the weak interaction length, in the Born approximation, we obtain expressions for neutrons’ gravitational scattering amplitudes. We calculate the influence of gravitational scattering on the asymmetry (forward vs. backward) in scattering of neutrons interacting with nuclei, for neutron energies from 10−10 eV (ultra-cold neutrons) to a few GeV. An analysis of the results shows that, with the existing accuracy, experiments of this king can hardly test the idea of multidimensional gravity.

The diversity of universes created by pure gravity

We show that a number of problems of modern cosmology may be solved in the framework of multidimensional gravity with high-order curvature invariants, without invoking other fields. We use a method employing a slow-change approximation, able to work with rather a general form of the gravitational action, and consider Kaluza–Klein type spacetimes with one or several extra factor spaces. A vast choice of effective theories suggested by the present framework may be stressed: even if the initial Lagrangian is entirely fixed, one obtains quite different models for different numbers, dimensions and topologies of the extra factor spaces. As examples of problems addressed we consider (i) explanation of the present accelerated expansion of the universe, with a reasonably small cosmological constant, and the problem of its fine tuning is considered from a new point of view; (ii) the mechanism of closed wall production in the early universe; such walls are necessary for massive primordial black hole formation which is an important stage in some scenarios of cosmic structure formation; (iii) sufficient particle production rate at the end of inflation; (iv) the possible existence of spatial domains in our universe with a macroscopic size of extra dimensions. We also discuss chaotic attractors appearing at possible nodes of the kinetic term of the effective scalar field Lagrangian.

1010 細胞間ネットワークの抑制が多方向重力環境下の骨細胞に及ぼす影響(S03-2 細胞・生体分子のバイオメカニクス(2),S03 細胞・生体分子のバイオメカニクス)

1010 細胞間ネットワークの抑制が多方向重力環境下の骨細胞に及ぼす影響(S03-2 細胞・生体分子のバイオメカニクス(2),S03 細胞・生体分子のバイオメカニクス)

SPIN PRECESSION IN THE DVALI–GABADADZE–PORRATI BRANEWORLD SCENARIO

In this letter, we work out the secular precession of the spin of a gyroscope in geodesic motion around a central mass in the framework of the Dvali–Gabadadze–Porrati multidimensional gravity model. Such an effect, which depends on the mass of the central body and on the orbit radius of the gyroscope, contrary to the precessions of the orbital elements of the orbit of a test body, is far too small to be detected.

Bone marrow cell differentiation regulated by gel-embedded osteocyte under multi-dimensional gravity

Bone marrow cell differentiation regulated by gel-embedded osteocyte under multi-dimensional gravity

211 多方向重力場が骨細胞のサイトカイン産生に及ぼす影響(OS1-3 再生医工学(3),オーガナイズドセッション1:細胞・組織・器官のバイオメカニクス/再生医工学,学術講演)

211 多方向重力場が骨細胞のサイトカイン産生に及ぼす影響(OS1-3 再生医工学(3),オーガナイズドセッション1:細胞・組織・器官のバイオメカニクス/再生医工学,学術講演)

多方向重力負荷による骨細胞の力学応答

微小重力環境における長期滞在や高齢社会により増加傾向にある長期臥床患者では骨量減少による生活の質の低下が問題となっている. 骨量減少を抑止するには骨量減少のメカニズムを解明することが必須である. 骨は機械的刺激に応答してリモデリング (再構築) を行う組織であることから, 解明には力学的側面からのアプローチが重要である. そこで本研究では, 擬微小重力環境を発生させる多方向重力負荷培養システムを新たに開発した. 骨組織の中で機械的刺激を感受する骨細胞を用いて, 多方向重力環境が細胞の機能や分化に及ぼす影響を調査した. その結果, 多方向重力環境にさらされた骨細胞は細胞増殖能および細胞間情報伝達能が有意に抑制されること, 骨細胞の培養液上清を用いた骨髄細胞の培養において骨髄細胞から破骨細胞様細胞への分化を有意に増加させることが明らかになった.

Oscillatory regime in the multidimensional homogeneous cosmological models induced by a vector field

We show that in multidimensional gravity, vector fields completely determine the structure and properties of singularity. It turns out that in the presence of a vector field the oscillatory regime exists in all spatial dimensions and for all homogeneous models. By analysing the Hamiltonian equations we derive the Poincaré return map associated with the Kasner indexes and fix the rules according to which the Kasner vectors rotate. In correspondence to a four-dimensional spacetime, the oscillatory regime here constructed overlaps the usual Belinski–Khalatnikov–Liftshitz one.

1223 多方向重力場に置かれた三次元培養骨細胞の機能調整(G02-3 骨梁構造とリモデリング,G02 バイオエンジニアリング)

Microgravity induces osteoporosis. Osteocytes are considered to act as a mechanosensor in bone tissue. They are the most abundant cells in bone and distribute throughout the bone matrix. However, very little is known about detail mechanism of osteoporosis occurred under microgravity. We have already reported that microgravity influenced cell proliferation, cell-to-cell communication and differentiation of bone marrow cells when osteocyte-like cell line MLO-Y4 cells were cultured in monolayer and subjected to multi-dimensional gravity. However, osteocytes in vivo were deep embedded in bone matrix. Therefore, the aim of this study was to examine the effects of multi-dimensional gravity on osteocytes in three-dimensional culture. MLO-Y4 cells were cultured in type I collagen gel, and then exposed to multi-dimensional gravity for 24h. Double fluorescence staining technique revealed that cell-to-cell communications via gap junction were significantly decreased in multi-dimensional gravity. Bone marrow cells were cultured for a week with using conditioned medium (CM) obtained from osteocyte culture under multidimensional gravity. TRAP (tartrate-resistant acid phosphatase) activity was significantly increased by adding CM from osteocyte culture exposed to multi-dimensional gravity.

101 多方向重力環境で培養した骨細胞が骨髄細胞に与える影響(OS1-01 : 細胞の物理刺激応答(1),マイクロ・ナノバイオメカニクス)

101 多方向重力環境で培養した骨細胞が骨髄細胞に与える影響(OS1-01 : 細胞の物理刺激応答(1),マイクロ・ナノバイオメカニクス)

517 骨細胞に対する多方向重力環境の影響(O.S.1:臨床応用に向けたバイオメカニクス,九州支部 第58期総会・講演会)

517 骨細胞に対する多方向重力環境の影響(O.S.1:臨床応用に向けたバイオメカニクス,九州支部 第58期総会・講演会)