Jay D. Tasson
The production of low-energy antimatter provides unique opportunities to search for new physics in an unexplored regime. Testing gravitational interactions with antimatter is one such opportunity. Here a scenario based on Lorentz and CPT violation in the Standard- Model Extension is considered in which anomalous gravitational effects in antimatter could arise.
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The gravitational field of matter and that of antimatter could differ. This might be one signature of quantum gravity. We show that primordial Big Bang Nucleosynthesis restricts such a possibility.
We propose an experimental test of the gravitational interaction with antimatter by measuring the branching fraction of the CP~violating decay $K_\mathrm{L} \to π^{+} π^{-}$ in space. We show that at the altitude of the International Space Station, gravitational effects may change the level of CP~violation such that a 5$σ$ discrimination may be obtained by collecting the $K_\mathrm{L}$ produced by the cosmic proton flux within a few years.
Support for Gravitationally-Attractive Composite Antimatter and Gravitationally-Repulsive Non-composite Antimatter
本文指出ALPHA实验仅测量了复合反物质（反氢）的引力效应，提出价反夸克等非复合反物质可能受地球引力排斥，并建议通过反夸克与引力场直接相互作用实验及AMS-01数据验证。
Certain modern theories of gravity predict that antimatter will fall differently than matter in the Earth's gravitational field. However, no experimental tests of gravity on antimatter exist and all conclusions drawn from experiments on matter depend, at some level, on a specific model. We have proposed a direct measurement that would compare the gravitational acceleration of antiprotons to that of negatively charged hydrogen ions. Substantial progress towards the development of this experiment has been achieved. Based on our work a number of alternative proposals for measuring ``$g$" on both …
Aspects of matter-antimatter asymmetries in relativistic heavy ions collisions and Astroparticle Physics
该研究基于强相互作用相图思路，以自发对称性破缺等效应为基础，探讨相对论重离子碰撞与早期宇宙中的物质-反物质不对称性，假设无需依赖非平衡条件。
Provided that matter-antimatter domains are present at the onset of big bang nucleosynthesis (BBN), the number of allowed additional relativistic species increases, compared to the standard scenario when matter-antimatter domains are absent. The extra relativistic species may take the form of massless fermions or even massless bosons, like relic gravitons. The number of additional degrees of freedom compatible with BBN depends, in this framework, upon the typical scale of the domains and the antimatter fraction. Since the presence of matter-antimatter domains allows a reduction of the neutron …
We review the experimental evidence for a net baryon density in cosmology, and the theoretical mechanism for producing it, called leptogenesis, which relies on the creation of a lepton asymmetry at an intermediate step. The naturality of this mechanism and its possible relations with neutrino oscillations are outlined.
The universality of free fall, the weak equivalence principle (WEP), is a cornerstone of the general theory of relativity, the most precise theory of gravity confirmed in all experiments up to date. The WEP states the equivalence of the inertial, $m$, and gravitational, $m_g$, masses and was tested in numerous occasions with normal matter at relatively low energies. However, there is no proof for the matter and antimatter at high energies. For the antimatter the situation is even less clear -- current direct observations of trapped antihydrogen suggest the limits $-65 < m_g / m < 110$ not excl…
The AEgIS collaboration is underway to directly measure the gravitational free-fall of neutral antimatter atoms. The experiment recently succeded in producing a pulsed cold antihydrogen source for the first time, and has now entered into its second phase, which aims at the formation of a slow antihydrogen beam and subseuqently a first proof-of-concept gravitational measurement. Major upgrades have been made, such as an improved antihydrogen production scheme and a new state-of-the-art antiproton trap. AEgIS was also connected to CERN's new antiproton deceleration facility ELENA and achieved fi…
General relativity (GR) is the current description of gravity in modern physics. One of the cornerstones of GR, as well as Newton's theory of gravity, is the weak equivalence principle (WEP), stating that the trajectory of a freely falling test body is independent of its internal structure and composition. WEP is known to be valid for the normal matter with a high precision. However, due to the rarity of antimatter and weakness of the gravitational forces, the WEP has never been confirmed for antimatter. The current direct bounds on the ratio between the gravitational and inertial masses of th…
The discovery of neutrino oscillations provides a solid evidence for nonzero neutrino masses and leptonic mixing. The fact that neutrino masses are so tiny constitutes a puzzling problem in particle physics. From the theoretical viewpoint, the smallness of neutrino masses can be elegantly explained through the seesaw mechanism. Another challenging issue for particle physics and cosmology is the explanation of the matter-antimatter asymmetry observed in Nature. Among the viable mechanisms, leptogenesis is a simple and well-motivated framework. In this talk we briefly review these aspects, makin…
We demonstrate how loop effects in gravitational backgrounds lead to a difference in the propagation of matter and antimatter, and show this is forbidden in flat space due to CPT and translation invariance. This mechanism, which is naturally present in beyond the standard model (BSM) theories exhibiting C and CP violation, generates a curvature-dependent chemical potential for leptons in the low-energy effective Lagrangian, allowing a matter-antimatter asymmetry to be generated in thermodynamic equilibrium, below the BSM scale.
We present a model for the Universe in which quantum anomalies are argued to play an important dual role: they are responsible for generating matter-antimatter asymmetry, but also provide time-dependent contributions to the vacuum energy density of "running-vacuum" type, which drive the Universe evolution. During the inflationary phase of a string-inspired Universe, and its subsequent exit, the existence of primordial gravitational waves induce gravitational anomalies, which couple to the Kalb-Ramond (KR)axion field of the massless gravitational string multiplet. Such anomalous CP violating in…
A number of experiments are currently underway on antimatter, particularly anti-hydrogen, to test whether the fundamental interactions behave the same way as for matter. Here we present a simple argument showing that a bound on a difference in gravitational forces exerted on matter and antimatter is already so severe that is goes well beyond the sensitivity of the above measurements.
The generation of a matter-antimatter asymmetry in the Universe may be induced by the propagation of fermions in non-trivial, spherically asymmetric (and hence Lorentz violating) gravitational backgrounds. Such backgrounds may characterise the epoch of the early universe. The key point in these models is that the background induces different dispersion relations, hence populations, between fermions and antifermions, and thus CPT Violation (CPTV) appears in thermal equilibrium. Species populations may freeze out leading to leptogenesis and baryogenesis. We consider here a string-inspired scenar…
Chemical evolution of antimatter domains in early Universe
研究早期宇宙中反物质领域在质子物质环境中的化学演化及生存条件与湮灭过程
The apparent dominance of matter over antimatter in our universe is an obvious and puzzling fact which cannot be adequately explained in present physical frameworks that assume matter-antimatter symmetry at the big bang. However, our present knowledge of starting conditions and of known sources of CP violation are both insufficient to explain the observed asymmetry. Therefore ongoing research on matter-antimatter differences is strongly motivated as well as attempts to identify viable new mechanisms that could create the present asymmetry. Here we concentrate on possible precision experiments …
Gravitational leptogenesis from metric perturbations
本文提出无需新轴耦合，利用暴胀后扰动时空度规破坏宇称产生Pontryagin密度，从而实现引力轻子生成，产生物质-反物质不对称性，并在某些暴胀和再加热情景下局部与观测相当。
The gravitational acceleration of antimatter, $\bar g$, has yet to be directly measured but could change our understanding of gravity, the Universe, and the possibility of a fifth force. Three avenues are apparent for such a measurement: antihydrogen, positronium, and muonium, the last requiring a precision atom interferometer and benefiting from a novel muonium beam under development. The interferometer and its few-picometer alignment and calibration systems appear to be feasible. With 100 nm grating pitch, measurements of $\bar g$ to 10%, 1%, or better can be envisioned. This could constitut…
Antimatter nuclei in cosmic rays (CRs) are a promising tool for the indirect detection of dark-matter annihilation signatures. However, the search of new-physics signals in CRs relies on our knowledge of the astrophysical antimatter background which, in turns, depends critically on the several fragmentation cross-sections that regulate production and destruction of antiparticles in the interstellar medium. In this work, we have re-evaluated the astrophysical background of CR antiproton, antineutron, and antihelium nuclei in Galactic CRs using improved calculations. The production cross-section…
Imprint of matter-antimatter asymmetry on collapsing domain walls
本文探讨了在有限温度下，由狄拉克费米子的大不对称性引起的辐射修正如何产生偏置项，从而影响塌缩域墙及引力波的产生。
Gravitational ABJ Anomaly, Stochastic Matter Production, and Leptogenesis
本研究提出早期宇宙部分手征随机引力波通过引力ABJ反常随机产生费米子物质的机制，可解释全部暗物质遗迹密度与宇宙物质-反物质不对称性，且引力波的暂时手征性会留下可保存的量子遗迹。
We know that the generally accepted theories of gravity and quantum mechanics are fundamentally incompatible. Thus, when we try to combine these theories, we must beware of physical pitfalls. Modern theories of quantum gravity are trying to overcome these problems. Any ideas must confront the present agreement with general relativity, but yet be free to wonder about not understood phenomena, such as the dark matter problem and the anomalous spacecraft data which we announce here. This all has led some ``intrepid" theorists to consider a new gravitational regime, that of antimatter. Even more `…
The Standard-Model Extension (SME) provides a comprehensive effective field-theory framework for the study of CPT and Lorentz symmetry. This work reviews the structure and philosophy of the SME and provides some intuitive examples of symmetry violation. The results of recent gravitational tests performed within the SME are summarized including analysis of results from the Laser Interferometer Gravitational-Wave Observatory (LIGO), sensitivities achieved in short-range gravity experiments, constraints from cosmic-ray data, and results achieved by studying planetary ephemerids. Some proposals an…
A Common Antimatter Response in AMS-02 Positrons and Antiprotons
基于AMS-02数据，提出反物质共同响应机制：反粒子（正电子和反质子）在高刚度区域具有相似的刚度依赖性，通过减少后产生延迟暴露而非额外源来解释。
In models with the fundamental gravity scale in the TeV range, early cosmology is quite different from the standard picture, because the universe must have arisen at a much lower temperature and the electroweak symmetry was probably never restored. In this context, baryogenesis appears to be problematic: if the involved physics is essentially that of the Standard Model, ``conventional'' non-conserving baryon number processes are completely negligible at such low temperatures. In this paper we show that the observed matter-antimatter asymmetry of the universe may be generated by gravitational d…
The recent advent of high precision antihydrogen spectroscopy opens the way to stringent experimental tests of the fundamental principles underlying particle physics and general relativity (GR), such as Lorentz and CPT invariance and the Einstein Equivalence Principle (EEP), on pure antimatter systems. In this paper, the nature and implications of these tests is investigated, with special reference to the ALPHA antihydrogen programme at CERN. This is underpinned by a theoretical review of the role of antiparticles, causality and fundamental symmetries in relativistic quantum field theory (QFT)…
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