High Energy Physics Theory Research Articles

Constraining ultralight axions with galaxy surveys

Ultralight axions and other bosons are dark matter candidates present in many high energy physics theories beyond the Standard Model. In particular, the string axiverse postulates the existence of up to \U0001d4aa(100) light scalar bosons constituting the dark sector. We test the validity of the effective field theory of large-scale structure approach to mixed ultralight axion dark matter by making our own mock galaxy catalogs and find an anisotropic ultralight axion signature in the galaxy quadrupole. We use the Fourier-space galaxy clustering statistics from the Baryon Oscillation Spectroscopic Survey (BOSS) and obtain upper bounds for the axion relic density Ω_a h2<0.004 for axions of mass 10-31 eV≤ m_a≤ 10-26 eV at 95% confidence. We also improve existing constraints by a factor of over 4.5 and 2.1 for axion masses of 10-25 eV and 10-32 eV compared to CMB alone. To improve the convergence speed of our analysis, we develop an augmented interpolation scheme allowing a fast computation of the axion contribution to the linear matter power spectrum. This method leads to a 70% reduction of the computational cost for the full Monte Carlo Markov chains analysis.

Ultrarelativistic polarized positron jets via collision of electron and ultraintense laser beams

Relativistic spin-polarized positron beams are indispensable for future electron-positron colliders to test modern high-energy physics theory with high precision. However, present techniques require very large scale facilities for those experiments. We put forward a novel efficient method for generating ultrarelativistic polarized positron beams employing currently available laser fields. For this purpose, the generation of polarized positrons via multiphoton Breit-Wheeler pair production and the associated spin dynamics in single-shot interaction of an ultraintense laser pulse with an ultrarelativistic electron beam is investigated in the quantum radiation-dominated regime. The pair production spin asymmetry in strong fields, significantly exceeding the asymmetry of the radiative polarization, produces locally highly polarized particles, which are split by a specifically tailored small ellipticity of the laser field into two oppositely polarized beams along the minor axis of laser polarization. In spite of radiative de-polarization, a dense positron beam with up to about 90% polarization can be generated in tens of femtoseconds. The method may eventually usher high-energy physics studies into smaller-scale laser laboratories.

Homophyly/kinship hypothesis: Natural communities, and predicting in networks

It has been a longstanding challenge to understand natural communities in real world networks. We proposed a community finding algorithm based on fitness of networks, two algorithms for prediction, accurate prediction and confirmation of keywords for papers in the citation network Arxiv HEP-TH (high energy physics theory), and the measures of internal centrality, external de-centrality, internal and external slopes to characterize the structures of communities. We implemented our algorithms on 2 citation and 5 cooperation graphs. Our experiments explored and validated a homophyly/kinship principle of real world networks. The homophyly/kinship principle includes: (1) homophyly is the natural selection in real world networks, similar to Darwin’s kinship selection in nature, (2) real world networks consist of natural communities generated by the natural selection of homophyly, (3) most individuals in a natural community share a short list of common attributes, (4) natural communities have an internal centrality (or internal heterogeneity) that a natural community has a few nodes dominating most of the individuals in the community, (5) natural communities have an external de-centrality (or external homogeneity) that external links of a natural community homogeneously distributed in different communities, and (6) natural communities of a given network have typical structures determined by the internal slopes, and have typical patterns of outgoing links determined by external slopes, etc. Our homophyly/kinship principle perfectly matches Darwin’s observation that animals from ants to people form social groups in which most individuals work for the common good, and that kinship could encourage altruistic behavior. Our homophyly/kinship principle is the network version of Darwinian theory, and builds a bridge between Darwinian evolution and network science.

Approximate von Neumann entropy for directed graphs.

In this paper, we develop an entropy measure for assessing the structural complexity of directed graphs. Although there are many existing alternative measures for quantifying the structural properties of undirected graphs, there are relatively few corresponding measures for directed graphs. To fill this gap in the literature, we explore an alternative technique that is applicable to directed graphs. We commence by using Chung's generalization of the Laplacian of a directed graph to extend the computation of von Neumann entropy from undirected to directed graphs. We provide a simplified form of the entropy which can be expressed in terms of simple node in-degree and out-degree statistics. Moreover, we find approximate forms of the von Neumann entropy that apply to both weakly and strongly directed graphs, and that can be used to characterize network structure. We illustrate the usefulness of these simplified entropy forms defined in this paper on both artificial and real-world data sets, including structures from protein databases and high energy physics theory citation networks.

Chameleon gravity, electrostatics, and kinematics in the outer galaxy

Light scalar fields are expected to arise in theories of high energy physics (such as string theory), and find phenomenological motivations in dark energy, dark matter, or neutrino physics. However, the coupling of light scalar fields to ordinary (or dark) matter is strongly constrained from laboratory, solar system, and astrophysical tests of the fifth force. One way to evade these constraints in dense environments is through the chameleon mechanism, where the field's mass steeply increases with ambient density. Consequently, the chameleonic force is only sourced by a thin shell near the surface of dense objects, which significantly reduces its magnitude.In this paper, we argue that thin-shell conditions are equivalentto ``conducting'' boundary conditions in electrostatics. As anapplication, we use the analogue of the method of images tocalculate the back-reaction (or self-force) of an object around aspherical gravitational source. Using this method, we canexplicitly compute the violation of the equivalence principle in theoutskirts of galactic haloes (assuming an NFW dark matterprofile): Intermediate mass satellites can be slower than theirlarger/smaller counterparts by as much as 10% close to a thinshell.

Phenomenology of gravitational aether as a solution to the old cosmological constant problem

One of the deepest and most long-standing mysteries in physics has been the huge discrepancy between the observed vacuum density and our expectations from theories of high energy physics, which has been dubbed the Old Cosmological Constant problem. One proposal to address this puzzle at the semi-classical level is to decouple quantum vacuum from space-time geometry via a modification of gravity that includes an incompressible fluid, known as Gravitational Aether. In this paper, we discuss classical predictions of this theory along with its compatibility with cosmological and experimental tests of gravity. We argue that deviations from General Relativity (GR) in this theory are sourced by pressure or vorticity. In particular, the theory predicts that the gravitational constant for radiation is 33% larger than that of non-relativistic matter, which is preferred by (most) cosmic microwave background (CMB), Lyman-Alpha forest, and Lithium-7 primordial abundance observations, while being consistent with other cosmological tests at ~2-sigma level. It is further shown that all Parametrized Post-Newtonian (PPN) parameters have the standard GR values aside from the anomalous coupling to pressure, which has not been directly measured. A more subtle prediction of this model (assuming irrotational aether) is that the (intrinsic) gravitomagnetic effect is 33% larger than GR prediction. This is consistent with current limits from LAGEOS and Gravity Probe B at ~2-sigma level.

Fundamental constants and their variability in theories of high energy physics

The Standard Model of particle physics and the theory of General Relativity (GR) currently provide a good description of almost all phenomena of particle physics and gravitation that have received controlled experimental tests. However, the Standard Model contains many a priori variable parameters whose values, and whose apparent (near-)constancy, have yet to receive a convincing theoretical explanation. At the same time, GR may now require to be extended or altered at the largest length scales, to account for the recent apparent accelerated cosmological expansion. In this introductory review I present theoretical aspects of the search for explanations of the values and possible variations of fundamental “constants”, focusing on the possibility of unification of interactions. I also relate cosmological variations to modifications of gravity both locally and cosmologically.

A parametric model for dark energy

Determining the mechanism behind the current cosmic acceleration constitutes a major question nowadays in theoretical physics. If the dark energy route is taken, this problem may potentially bring to light new insights not only in cosmology but also in high energy physics theories. Following this approach, we explore in this Letter some cosmological consequences of a new time-dependent parameterization for the dark energy equation of state (EoS), which is a well behaved function of the redshift z over the entire cosmological evolution, i.e., z∈[−1,∞). This parameterization allows us to divide the parametric plane (w0,w1) in defined regions associated to distinct classes of dark energy models that can be confirmed or excluded from a confrontation with current observational data. By assuming a flat universe, a statistical analysis involving the most recent observations from type Ia supernovae, baryon acoustic oscillation peak, Cosmic Microwave Background shift parameter and Hubble evolution H(z) is performed to check the observational viability of the EoS parameterization here proposed.

A Cosmic Microwave Background Feature Consistent with a Cosmic Texture

The Cosmic Microwave Background provides our most ancient image of the universe and our best tool for studying its early evolution. Theories of high-energy physics predict the formation of various types of topological defects in the very early universe, including cosmic texture, which would generate hot and cold spots in the Cosmic Microwave Background. We show through a Bayesian statistical analysis that the most prominent 5°-radius cold spot observed in all-sky images, which is otherwise hard to explain, is compatible with having being caused by a texture. From this model, we constrain the fundamental symmetry-breaking energy scale to be ϕ0 ≈ 8.7 × 1015 gigaelectron volts. If confirmed, this detection of a cosmic defect will probe physics at energies exceeding any conceivable terrestrial experiment.

Freudental magic square and its dimensional implication for [formula omitted] and high energy physics

Modern theories of high energy physics are based in one way or another on Lie symmetry group’s considerations. In particular the exceptional family plays a pivotal role in superstring and E-infinity theory. For a long time the very existence of the famous 5 exceptional Lie groups G 2, F 4, E 6, E 7 and E 8 with dimensions 14; 52, 78, 133 and 248 was bizarre. Freudental magic square gives some reasons to believe that the exceptional groups are not that exceptional. In the present work we elaborate this point further still and show that the sum of the dimension of E 8, E 7 and E 6 when adding the dimensions of the two grand unification groups SO(10) and SU(4) to them amounts to the number of states in Witten’s p = 5 Brane model, namely 528. Furthermore when taking the standard model SU(3) SU(2) U(1) and an eight degrees of freedom Higgs field into account, the number rises to 4 multiplied with 137 of the inverse electromagnetic fine structure constant 528 + 12 + 8 = 4 α ¯ 0 = ( 4 ) ( 137 ) = 548 . The general implications of these results for high energy physics are briefly discussed.

A Cosmic Microwave Background Feature Consistent with a Cosmic Texture

The Cosmic Microwave Background provides our most ancient image of the universe and our best tool for studying its early evolution. Theories of high-energy physics predict the formation of various types of topological defects in the very early universe, including cosmic texture, which would generate hot and cold spots in the Cosmic Microwave Background. We show through a Bayesian statistical analysis that the most prominent 5 degrees -radius cold spot observed in all-sky images, which is otherwise hard to explain, is compatible with having being caused by a texture. From this model, we constrain the fundamental symmetry-breaking energy scale to be (0) approximately 8.7 x 10(15) gigaelectron volts. If confirmed, this detection of a cosmic defect will probe physics at energies exceeding any conceivable terrestrial experiment.

Ranking scientific publications using a model of network traffic

To account for strong ageing characteristics of citation networks, we modify thePageRank algorithm by initially distributing random surfers exponentially with age, infavour of more recent publications. The output of this algorithm, which we callCiteRank, is interpreted as approximate traffic to individual publications in a simplemodel of how researchers find new information. We optimize parameters of ouralgorithm to achieve the best performance. The results are compared for tworather different citation networks: all American Physical Society publicationsbetween 1893 and 2003 and the set of high-energy physics theory (hep-th) preprints.Despite major differences between these two networks, we find that their optimalparameters for the CiteRank algorithm are remarkably similar. The advantages andperformance of CiteRank over more conventional methods of ranking publications arediscussed.

Exploring the expansion history of the universe.

Exploring the recent expansion history of the universe promises insights into the cosmological model, the nature of dark energy, and potentially clues to high energy physics theories and gravitation. We examine the extent to which precision distance-redshift observations can map out the history, including the acceleration-deceleration transition, and the components and equations of state of the energy density. We consider the ability to distinguish between various dynamical scalar field models for the dark energy, as well as higher dimension and alternate gravity theories. Finally, we present a new, advantageous parametrization for the study of dark energy.

Possible evidence for a variable fine-structure constant from QSO absorption lines: motivations, analysis and results

An experimental search for variation in the fundamental coupling constants is strongly motivated by modern high-energy physics theories. Comparison of quasar (QSO) absorption-line spectra with laboratory spectra provides a sensitive probe for variability of the fine-structure constant, α, over cosmological time-scales. We have previously developed and applied a new method providing an order-of-magnitude gain in precision over previous optical astrophysical constraints. Here we extend that work by including new quasar spectra of damped Lyman-α absorption systems. We also reanalyse our previous lower-redshift data and confirm our initial results. The constraints on α come from simultaneous fitting of absorption lines of subsets of the following species: Mg-i, Mg-ii, Al-ii, Al-iii, Si-ii, Cr-ii, Fe-ii, Ni-ii and Zn-ii. We present a detailed description of our methods and results based on an analysis of 49 quasar absorption systems (towards 28 QSOs) covering the redshift range . There is statistical evidence for a smaller α at earlier epochs: The new and original samples are independent but separately yield consistent and significant non-zero values of . We summarize the results of a thorough investigation of systematic effects published in a companion paper. The value we quote above is the raw value, not corrected for any of these systematic effects. The only significant systematic effects so far identified, if removed from our data, would lead to a more significant deviation of from zero.

Universal Algebraic Varieties and Ideals in Physics: Field Theory on Algebraic Varieties

A class of universal algebraic varieties in physics is discussed herein using the concepts of determinant ideals in algebraic geometry. It is shown that these algebraic varieties arise with very different physical contexts in many branches of physics and mathematics from high energy physics theory to chaos theory. In these physical systems the models are constructed by using the fields on usual manifolds such as vector fields in a Euclidean space and a Minkowskian space. But there is a universal mathematical aspect of linear algebra for linear vector spaces, where the linear independency and dependency are described using the Gramians of the vectors. These Gramians form a class of hypersurfaces in a higher-dimensional mathematical space: If there exist g vectors vi in an n-dimensional Euclidean space, the Gramian Gg is given as a g × g determinant Gg= Det [xij] with the inner products xij=(vi,vj), and exists in a g(g-1)/2-[g(g+1)/2-] dimensional space if the vectors are (not) normalized, xii=1(xii ≠ 1). It is also shown that the Gramians are invariant under automorphisms of the vectors. The mathematical structure of the Gramians is revealed to be equivalent to the concepts of determinant ideals Ig(v), each element of which is a g × g determinant constructed from components of an arbitrary N×N matrix with N&gt;n and which have inclusion relation: R=I0(v)⊃ I1(v) ⊃···⊃ Ig(v) ⊃···, and Ig(v)=0 if g&gt;n. In the various physical systems the ideals naturally emerge to give us dynamical flows on the hypersurfaces, and therefore, it is called the field theory on algebraic varieties. This viewpoint provides us a grand viewpoint in physics and mathematics.

Material content of the Universe: chairman's introduction

The question before us at this Discussion Meeting differs from many of the fundamental problems of contemporary science in that it can be stated concisely without the introduction of technicalities: how much material is there in the Universe and in what forms does it reside? This simple question appears to possess a very convoluted and, as yet, incomplete answer. It has become clear that a satisfactory answer to it must go hand-in-hand with the development of a mature theory of how galaxies form and cluster, together with an understanding of the complete catalogue of elementary particle types that exist in Nature. The reason for this last stipulation has only been adequately recognized during the last six years, throughout which astronomers have witnessed burgeoning interest in the possibility that the Universe may consist primarily of weakly interacting elementary particles of a sort as yet undetected in terrestrial laboratories. This interest has been motivated by the success of the high-energy physics theories that predict the existence of such particles and by the accumulation of observational evidence for the existence of large quantities of non-luminous matter in the Universe.