ESSAY: The Cosmological Constant Problem in Brane-Worlds and Gravitational Lorentz Violations

Brane worlds are theories with extra spatial dimensions in which ordinary matter is localized on a (3+1) dimensional submanifold. Such theories could have interesting consequences for particle physics and gravitational physics. In this essay we concentrate on the cosmological constant (CC) problem in the context of brane worlds. We show how extra-dimensional scenarios may violate Lorentz invariance in the gravity sector of the effective 4D theory, while particle physics remains unaffected. In such theories the usual no-go theorems for adjustment of the CC do not apply, and we indicate a possible explanation of the smallness of the CC. Lorentz violating effects would manifest themselves in gravitational waves travelling with a speed different from light, which can be searched for in gravitational wave experiments.     

Relationship between the symmetry energy and the single-nucleon potential in isospin-asymmetric nucleonic matter

When skyrmions representing nucleons are put on crystal lattice and compressed to simulate high density, there is a transition above the normal nuclear matter density (n₀) from a matter consisting of skyrmions with integer baryon charge to a state of half-skyrmions with half-integer baryon charge. We exploit this observation in an effective field theory framework to access dense baryonic system. We find that the topology change involved in the transition implies changeover from a Fermi liquid structure to a non-Fermi liquid with the chiral condensate in the “melted-off” nucleon. The ～ 80% of the nucleon mass that remains “unmelted”, invariant under chiral transformation, points to the possible origin of the (bulk of) proton mass that is not encoded in the standard mechanism of spontaneously broken chiral symmetry. The topology change engenders a drastic modification of the nuclear tensor forces, thereby non-trivially affecting the EoS, in particular, the symmetry energy, for compact star matter. It brings in stiffening of the EoS needed to accommodate a neutron star of ～ 2 solar mass. The strong effect on the EoS in general and in the tensor force structure in particular will also have impact on processes that could be measured at RIB-type accelerators.     

Assessment of Neutron Star Equation of State by Gravitational Waves

The possibility of assessing the equation of state of the neutron star matter using gravitational waves is briefly sketched. The effective theory recently proposed in the frame work of the scale-invariant hidden local symmetry is discussed to demonstrate its particular feature of a change over in EoS from lower density to higher density. The possible implications on the gravitational waves from coalescing binary neutron stars are discussed.     

Gauge eelations for spherical gravitational waves

Einstein gravitational waves radiated by an island system of arbitrary structure are analyzed. The effect of retardation on the wave structure can be dealt with vigorously by using Fourier series and switching to the Helmholtz equation. The Lorentz gauge and the strong conservation of the energy-momentum tensor of the matter determine each other unambiguously, so the introduction of gauge fields is unnecessary. It is not possible to suppress radiated waves of any type by means of the gauge. The most promising types of gravitational waves for gravitational-wave experiments are identified.Leningrad Electrotechnical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 107–111, October, 1992.     

Identifying the inflaton with primordial gravitational waves

We explore the ability of experimental physics to uncover the underlying structure of the gravitational Lagrangian describing inflation. While the observable degeneracy of the inflationary parameter space is large, future measurements of observables beyond the adiabatic and tensor two-point functions, such as non-gaussianity or isocurvature modes, might reduce this degeneracy. We show that, even in the absence of such observables, the range of possible inflaton potentials can be reduced with a precision measurement of the tensor spectral index, as might be possible with a direct detection of primordial gravitational waves.     

Galilean-invariant scalar fields can strengthen gravitational lensing

The mystery of dark energy suggests that there is new gravitational physics on long length scales. Yet light degrees of freedom in gravity are strictly limited by Solar System observations. We can resolve this apparent contradiction by adding a Galilean-invariant scalar field to gravity. Called Galileons, these scalars have strong self-interactions near overdensities, like the Solar System, that suppress their dynamical effect. These nonlinearities are weak on cosmological scales, permitting new physics to operate. In this Letter, we point out that a massive-gravity-inspired coupling of Galileons to stress energy can enhance gravitational lensing. Because the enhancement appears at a fixed scaled location for dark matter halos of a wide range of masses, stacked cluster analysis of weak lensing data should be able to detect or constrain this effect.     

A possible quark mechanism for the saturation of nuclear matter

A nuclear matter saturation mechanism based on the quark structure of the nucleon is proposed. Nuclear matter is described by nucleons and mesons but the meson field modifies the internal quark motion and this induces a saturation mechanism. Its possible relevance for nuclear physics is studied in a schematic model where it is the only active mechanism. Though caricatural, this model provides a rather satisfactory interpretation of the nuclear matter properties.     

天体物理、引力波及重离子碰撞中的物质

通过相对论性磁流体力学的计算知道,由双中子星合并产生的引力波对中子星内部是否存在夸克物质以及QCD物质状态方程的硬度度非常敏感。这些天文学上创造的热力学极限在20%以内跟某些快度、碰撞参数等条件下的相对论重离子碰撞产生的温度和密度相当。本文结合相对论模拟双中子星系统及实验室中重离子碰撞的结果,从而确定高密物质的状态方程和相结构。讨论了中子星合并后残留物的引力波发射,这将有助于了解夸克强子过渡的性质。     

Gravitational wave production at the end of inflation

We consider gravitational wave production due to parametric resonance at the end of inflation, or "preheating." This leads to large inhomogeneities that source a stochastic background of gravitational waves at scales inside the comoving Hubble horizon at the end of inflation. We confirm that the present amplitude of these gravitational waves need not depend on the inflationary energy scale. We analyze an explicit model where the inflationary energy scale is approximately 10{9} GeV, yielding a signal close to the sensitivity of Advanced Laser Interferometer Gravitational Wave Observatory and Big Bang Observer. This signal highlights the possibility of a new observational "window" into inflationary physics and provides significant motivation for searches for stochastic backgrounds of gravitational waves in the Hz to GHz range, with an amplitude on the order of Omega_{gw}(k)h{2} approximately 10{-11}.     

Gravitational decoherence of atomic interferometers

We study the decoherence of atomic interferometers due to the scattering of stochastic gravitational waves. We evaluate the “direct” gravitational effect registered by the phase of the matter waves as well as the “indirect” effect registered by the light waves used as beam-splitters and mirrors for the matter waves. Considering as an example the space project HYPER, we show that both effects are negligible for the presently studied interferometers. Received 15 February 2002 / Received in final form 12 April 2002 Published online 19 July 2002     

Cumulation processes in gravitational and inertial force fields and in zero gravity

The effect of gravitational and inertial forces on precision cumulation of fast flows of matter, bubbles, and detonation and shock waves is studied. Possible effects on the motion of masses and waves, whose velocity, direction, and structure change, and on the change in the properties of the medium in front of waves, causing the parameters of the waves to change and giving rise to refraction, are noted. The advantages of doing experiments with precision cumulation in zero gravity are indicated. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 9, 748–751 (10 May 1996)     

Physics and the explanation of life

It is proposed to consider present-day physics as dealing with a special situation, the situation in which the phenomena of life and consciousness play no role. It is pointed out that physical theory has often dealt, in the past, with similarly special situations. Planetary theory neglects all but gravitational forces, macroscopic physics neglects fluctuations due to the atomic structure of matter, nuclear physics disregards weak and gravitational interactions. In some of these cases, physicists were well aware of dealing with special situations, or limiting cases as they are called in the article; in other cases, they were not. It is pointed out that, even if it were true that present-day physics accurately describes the motion of the physical constituents of living bodies, it would not give the whole story. Arguments are adduced, however, to show that the laws of physics, applicable for inanimate matter, will have to be modified when dealing with the more general situation in which life and consciousness play significant roles.The present article is a somewhat revised version of the address presented by the writer at the 1969 AAAS meeting in Boston, Mass.     

核外环境对衰变率的影响

核衰变速率是否受核外环境影响, 一直是核物理研究的热点问题。 这一问题不仅对核物理基础研究很重要, 而且与天体物理、 地质年代学、 凝聚态物理和核废物处理等都有重要关系。 旨在对这方面研究工作的进展做一介绍。The possible change of nuclear decay rates in different environments has long been an interesting topic due to its importance not only in nuclear physics but also in astrophysics, geological dating, condensed matter physics, disposal of nuclear waste etc. The progresses in the investigation of variations in nuclear decay rates are reviewed.     

Leptogenesis from gravity waves in models of inflation

We present a new mechanism for creating the observed cosmic matter-antimatter asymmetry which satisfies all three Sakharov conditions from one common thread, gravitational waves. We generate lepton number through the gravitational anomaly in the lepton number current. The source term comes from elliptically polarized gravity waves that are produced during inflation if the inflaton field contains a CP-odd component. The amount of matter asymmetry generated in our model can be of realistic size for the parameters within the range of some inflationary scenarios and grand unified theories.     

On the gravitodynamics of moving bodies

In the present work we propose a generalization of Newton’s gravitational theory from the original works of Heaviside and Sciama, that takes into account both approaches, and accomplishes the same result in a simpler way than the standard cosmological approach. The established formulation describes the local gravitational field related to the observables and effectively implements the Mach’s principle in a quantitative form that retakes Dirac’s large number hypothesis. As a consequence of the equivalence principle and the application of this formulation to the observable universe, we obtain, as an immediate result, a value of Ω = 2. We construct a dynamic model for a galaxy without dark matter, which fits well with recent observational data, in terms of a variable effective inertial mass that reflects the present dynamic state of the universe and that replicates from first principles, the phenomenology proposed in MOND. The remarkable aspect of these results is the connection of the effect dubbed dark matter with the dark energy field, which makes it possible for us to interpret it as longitudinal gravitational waves.     

Environmental effects on nuclear decay rates

The possible change of nuclear decay rates in different environments has long been an interesting topic due to its importance not only in nuclear physics but also in astrophysics, geological dating, condensed matter physics, etc. The progress in the investigation of variations in nuclear decay rates are reviewed.     

Environmental effects on nuclear decay rates

The possible change of nuclear decay rates in different environments has long been an interesting topic due to its importance not only in nuclear physics but also in astrophysics, geological dating, condensed matter physics, etc. The progress in the investigation of variations in nuclear decay rates are reviewed.     

致密物质状态方程:中子星与奇异星

中子星结构一直是核物理、粒子物理和天体物理共同关注的热点难题,双中子星并合事件GW170817的发现更是掀起这一研究的高潮。致密物质的状态方程是决定中子星结构的关键输入量,但是到目前为止,高密度的核物质状态方程行为依然很难确定。如今国内外已有许多运行或规划的大型核实验装置和天文观测设备,有望帮助我们很快解开致密物质状态方程的谜团。本文系统地阐述了基于微观多体理论和唯象模型对脉冲星类天体状态方程的研究现状,也讨论了奇异相变和奇异物质。结合理论计算和核物理实验及天文观测数据,致密物质状态方程的研究已取得相当多进展,但是也面临不少挑战,比如从实验和观测数据提取状态方程信息时的模型依赖,中子星各部分模型的不自洽以及各种依赖热密物质复杂动力学性质的实验和观测量。随着LIGO即将再运行而发现更多双中子星甚至中子星-黑洞等并合事件,多信使天文观测可望最终揭开中子星结构之谜。The matter state inside neutron stars (NSs) is an exciting problem in nuclear physics, particle physics and astrophysics. The equation of state (EOS) of NSs plays a crucial role in the present multimessenger astronomy, especially after the event of GW170817. Thanks to accruing studies with advanced telescopes and radioactive beam facilities, the unknown EOS of supranuclear matter could soon be understood. We review the current status of the EOS for pulsar-like compact objects, that have been studied with both microscopic many-body approaches and phenomenological models. The appearance of strange baryonic matter and strange quark matter are also discussed. We compare the theoretical predictions with different data coming from both nuclear physics experiments and astrophysical observations. Despite great progresses obtained in dense nuclear matter properties, there are various challenges ahead, such as the model dependence of the constraints extracted from either experimental or observational data, the lack of a consistent and rigorous many-body treatment of all parts of the star, the dependence of many observables on the turbulent dynamics of relevant hot dense system. As LIGO is about to run again and discover more NS merger events, multimessenger observations are expected to finally unravel the mystery of NS structure.     

Glimmers of a Pre-geometric Perspective

Spacetime measurements and gravitational experiments are made by using objects, matter fields or particles and their mutual relationships. As a consequence, any operationally meaningful assertion about spacetime is in fact an assertion about the degrees of freedom of the matter (i.e. non gravitational) fields; those, say for definiteness, of the Standard Model of particle physics. As for any quantum theory, the dynamics of the matter fields can be described in terms of a unitary evolution of a state vector in a Hilbert space. By writing the Hilbert space as a generic tensor product of “subsystems” we analyse the evolution of a state vector on an information theoretical basis and attempt to recover the usual spacetime relations from the information exchanges between these subsystems. We consider generic interacting second quantized models with a finite number of fermionic degrees of freedom and characterize on physical grounds the tensor product structure associated with the class of “localized systems” and therefore with “position”. We find that in the case of free theories no spacetime relation is operationally definable. On the contrary, by applying the same procedure to the simple interacting model of a one-dimensional Heisenberg spin chain we recover the tensor product structure usually associated with “position”. Finally, we discuss the possible role of gravity in this framework.     

Gravitational structure formation, the cosmological problem and statistical physics

Models of structure formation in the universe postulate that matter distributions observed today in galaxy catalogs arise, through a complex non-linear dynamics, by gravitational evolution from a very uniform initial state. Dark matter plays the central role of providing the primordial density seeds which will govern the dynamics of structure formation. We critically examine the role of cosmological dark matter by considering three different and related issues: Basic statistical properties of theoretical initial density fields, several elements of the gravitational many-body dynamics and key correlation features of the observed galaxy distributions are discussed, stressing some useful analogies with known systems in modern statistical physics.