Showing papers on "Elementary particle published in 2019"
TL;DR: Angle-resolved photoemission spectroscopy measurements in CoSi reveal the presence of unconventional chiral fermions near the Fermi level, with giant surface Ferm i arcs and one pair of well separated chiral nodes.
Abstract: Chirality—the geometric property of objects that do not coincide with their mirror image—is found in nature, for example, in molecules, crystals, galaxies and life forms. In quantum field theory, the chirality of a massless particle is defined by whether the directions of its spin and motion are parallel or antiparallel. Although massless chiral fermions—Weyl fermions—were predicted 90 years ago, their existence as fundamental particles has not been experimentally confirmed. However, their analogues have been observed as quasiparticles in condensed matter systems. In addition to Weyl fermions1–4, theorists have proposed a number of unconventional (that is, beyond the standard model) chiral fermions in condensed matter systems5–8, but direct experimental evidence of their existence is still lacking. Here, by using angle-resolved photoemission spectroscopy, we reveal two types of unconventional chiral fermion—spin-1 and charge-2 fermions—at the band-crossing points near the Fermi level in CoSi. The projections of these chiral fermions on the (001) surface are connected by giant Fermi arcs traversing the entire surface Brillouin zone. These chiral fermions are enforced at the centre or corner of the bulk Brillouin zone by the crystal symmetries, making CoSi a system with only one pair of chiral nodes with large separation in momentum space and extremely long surface Fermi arcs, in sharp contrast to Weyl semimetals, which have multiple pairs of Weyl nodes with small separation. Our results confirm the existence of unconventional chiral fermions and provide a platform for exploring the physical properties associated with chiral fermions. Angle-resolved photoemission spectroscopy measurements in CoSi reveal the presence of unconventional chiral fermions near the Fermi level, with giant surface Fermi arcs and one pair of well separated chiral nodes.
291 citations
KEK1
TL;DR: In this article, the authors derived a limit on the scattering cross section of dark matter with electrons that extends down to sub-keV masses, closing a previously allowed wide region of parameter space.
Abstract: Sub-GeV dark matter particles up-scattered by cosmic rays gain enough kinetic energy to pass the thresholds of large volume detectors on Earth. We then use public Super-Kamiokande and MiniBooNE data to derive a novel limit on the scattering cross section of dark matter with electrons that extends down to sub-keV masses, closing a previously allowed wide region of parameter space. We finally discuss search strategies and prospects at existing and planned neutrino facilities.
135 citations
TL;DR: In this paper, the weak charge of the proton was measured using parity-violating (PV) polarized electron-proton scattering asymmetry, and the value of Q_W^p was derived from the predicted neutral electroweak force.
Abstract: The fields of particle and nuclear physics have undertaken extensive programs to search for evidence of physics beyond that explained by current theories. The observation of the Higgs boson at the Large Hadron Collider completed the set of particles predicted by the Standard Model (SM), currently the best description of fundamental particles and forces. However, the theory's limitations include a failure to predict fundamental parameters and the inability to account for dark matter/energy, gravity, and the matter-antimater asymmetry in the universe, among other phenomena. Given the lack of additional particles found so far through direct searches in the post-Higgs era, indirect searches utilizing precise measurements of well predicted SM observables allow highly targeted alternative tests for physics beyond the SM. Indirect searches have the potential to reach mass/energy scales beyond those directly accessible by today's high-energy accelerators. The value of the weak charge of the proton Q_W^p is an example of such an indirect search, as it sets the strength of the proton's interaction with particles via the well-predicted neutral electroweak force. Parity violation (invariance under spatial inversion (x,y,z) -> (-x,-y,-z)) is violated only in the weak interaction, thus providing a unique tool to isolate the weak interaction in order to measure the proton's weak charge. Here we report Q_W^p=0.0719+-0.0045, as extracted from our measured parity-violating (PV) polarized electron-proton scattering asymmetry, A_ep=-226.5+-9.3 ppb. Our value of Q_W^p is in excellent agreement with the SM, and sets multi-TeV-scale constraints on any semi-leptonic PV physics not described within the SM.
119 citations
TL;DR: In this paper, Togashi et al. presented a much improved equation of state for neutron star matter, QHC19, with a smooth crossover from the hadronic regime at lower densities to the quark regime at higher densities.
Abstract: We present a much improved equation of state for neutron star matter, QHC19, with a smooth crossover from the hadronic regime at lower densities to the quark regime at higher densities. We now use the Togashi et al.~equation of state (Togashi:2017), a generalization of the Akmal-Pandharipande-Ravenhall equation of state of uniform nuclear matter, in the entire hadronic regime; the Togashi equation of state consistently describes non-uniform as well as uniform matter, and matter at beta equilibrium without the need for an interpolation between pure neutron and symmetric nuclear matter. We describe the quark matter regime at higher densities with the Nambu--Jona--Lasinio model, now identifying tight constraints on the phenomenological universal vector repulsion between quarks and the pairing interaction between quarks arising from the requirements of thermodynamic stability and causal propagation of sound. The resultant neutron star properties agree very well with the inferences of the LIGO/Virgo collaboration, from GW170817, of the pressure vs. baryon density, neutron star radii, and tidal deformabilities. The maximum neutron star mass allowed by QHC19 is 2.35 $M_\odot$, consistent with all neutron star mass determinations.
110 citations
TL;DR: In this paper, the authors identify the origin of this shift as arising from the exponentiation of spin operators for the recently defined "minimally coupled" three-particle amplitudes of spinning particles coupled to gravity, in the large-spin limit.
Abstract: Long ago, Newman and Janis showed that a complex deformation $z\rightarrow z+i a$ of the Schwarzschild solution produces the Kerr solution. The underlying explanation for this relationship has remained obscure. The complex deformation has an electromagnetic counterpart: by shifting the Coloumb potential, we obtain the EM field of a certain rotating charge distribution which we term $\sqrt{\rm Kerr}$. In this note, we identify the origin of this shift as arising from the exponentiation of spin operators for the recently defined "minimally coupled" three-particle amplitudes of spinning particles coupled to gravity, in the large-spin limit. We demonstrate this by studying the impulse imparted to a test particle in the background of the heavy spinning particle. We first consider the electromagnetic case, where the impulse due to $\sqrt{\rm Kerr}$ is reproduced by a charged spinning particle; the shift of the Coloumb potential is matched to the exponentiated spin-factor appearing in the amplitude. The known impulse due to the Kerr black hole is then trivially derived from the gravitationally coupled spinning particle via the double copy.
90 citations
TL;DR: In this article, the authors review the complex but well-ordered scenario of the properties of the dark halos also in relation with those of the baryonic components they host.
Abstract: The distribution of the non-luminous matter in galaxies of different luminosity and Hubble type is much more than a proof of the existence of dark particles governing the structures of the Universe. Here, we will review the complex but well-ordered scenario of the properties of the dark halos also in relation with those of the baryonic components they host. Moreover, we will present a number of tight and unexpected correlations between selected properties of the dark and the luminous matter. Such entanglement evolves across the varying properties of the luminous component and it seems to unequivocally lead to a dark particle able to interact with the Standard Model particles over cosmological times. This review will also focus on whether we need a paradigm shift, from pure collisionless dark particles emerging from “first principles”, to particles that we can discover only by looking to how they have designed the structure of the galaxies.
87 citations
TL;DR: In this article, it was shown that in a theory where the low energy dynamics of the gravitons are governed by the Einstein-Hilbert action, any finite number of massive elementary higher spin particles with spin more than two cannot interact with gravity in a way that preserves causality.
Abstract: According to common lore, massive elementary higher spin particles lead to inconsistencies when coupled to gravity. However, this scenario was not completely ruled out by previous arguments. In this paper, we show that in a theory where the low energy dynamics of the gravitons are governed by the Einstein-Hilbert action, any finite number of massive elementary particles with spin more than two cannot interact with gravitons, even classically, in a way that preserves causality. This is achieved in flat spacetime by studying eikonal scattering of higher spin particles in more than three spacetime dimensions. Our argument is insensitive to the physics above the effective cut-off scale and closes certain loopholes in previous arguments. Furthermore, it applies to higher spin particles even if they do not contribute to tree-level graviton scattering as a consequence of being charged under a global symmetry such as ℤ2. We derive analogous bounds in anti-de Sitter space-time from analyticity properties of correlators of the dual CFT in the Regge limit. We also argue that an infinite tower of fine-tuned higher spin particles can still be consistent with causality. However, they necessarily affect the dynamics of gravitons at an energy scale comparable to the mass of the lightest higher spin particle. Finally, we apply the bound in de Sitter to impose restrictions on the structure of three-point functions in the squeezed limit of the scalar curvature perturbation produced during inflation.
74 citations
TL;DR: In this article, the authors present a new experiment based on the concept of a dielectric haloscope for the direct search of dark matter axions in the mass range of 40 to 400
Abstract: The axion emerges in extensions of the Standard Model that explain the absence of CP violation in the strong interactions. Simultaneously, it can provide naturally the cold dark matter in our universe. Several searches for axions and axion-like particles (ALPs) have constrained the corresponding parameter space over the last decades but no unambiguous hints of their existence have been found. The axion mass range below 1 meV remains highly attractive and a well motivated region for dark matter axions. In this White Paper we present a description of a new experiment based on the concept of a dielectric haloscope for the direct search of dark matter axions in the mass range of 40 to 400 $$\upmu \hbox {eV}$$
. This MAgnetized Disk and Mirror Axion eXperiment (MADMAX) will consist of several parallel dielectric disks, which are placed in a strong magnetic field and with adjustable separations. This setting is expected to allow for an observable emission of axion induced electromagnetic waves at a frequency between 10 to 100 GHz corresponding to the axion mass.
57 citations
TL;DR: In this paper, the photon coupling of axion-like particles at the level of 10−12 GeV−1 for masses between 5× 10−23 eV and 1.2 × 10−21 eV was investigated.
Abstract: Dark matter may consist of axion-like particles with ultra-low masses. Two-photon interactions of these particles affect the polarization of radiation propagating through the dark matter. Coherent oscillations of the Bose condensate of the particles induce periodic changes in the plane of polarisation of emission passing through the condensate. We estimate this effect and analyze MOJAVE VLBA polarization observations of bright downstream features in the parsec-scale jets of active galaxies. Through the non-observation of periodic changes in the polarization angle, we are able to constrain the photon coupling of the ultra-light dark-matter axion-like particles at the level of 10−12 GeV−1 for masses between ~ 5× 10−23 eV and ~ 1.2 × 10−21 eV.
50 citations
01 Aug 2019
TL;DR: In this paper, the authors discuss recent developments in the measurement and interpretation of EDMs, and assess proposed techniques for future experiments that could push experimental limits on T-violating BSM physics to the PeV scale.
Abstract: New fundamental particles at the mass scale of a few TeV c–2 could account for observed phenomena that cannot be explained by the standard model (SM) of particle physics, including the microscopic origin of dark matter and the macroscopic imbalance of matter over antimatter in the Universe. However, no beyond-the-SM (BSM) particles at the TeV scale have yet been detected at the Large Hadron Collider (LHC). With recent innovations, searches for time-reversal symmetry (T) violation through low-energy precision measurements of electric dipole moments (EDMs) of atoms and molecules have attained the sensitivity to detect indirect signatures of certain particles with masses of more than 10 TeV c–2. In this Perspective, we discuss recent developments in the measurement and interpretation of EDMs, and assess proposed techniques for future experiments that could push experimental limits on T-violating BSM physics to the PeV scale. Electric dipole moments (EDMs) of atoms and molecules are a sensitive probe for sources of time-reversal symmetry violation beyond the standard model. In this Perspective, we review recent progress in EDM searches with atoms and molecules and survey proposed next-generation experiments.
49 citations
TL;DR: In this paper, the topology of the electronic structure in PdBiSe using density functional theory calculations and bulk-sensitive soft x-ray angle-resolved photoemission spectroscopy was studied.
Abstract: Topological semimetals with different types of band crossings provide a rich platform to realize novel fermionic excitations, known as topological fermions. In particular, some fermionic excitations can be direct analogs of elementary particles in quantum field theory when both obey the same laws of physics in the low-energy limit. Examples include Dirac and Weyl fermions, whose solid-state realizations have provided new insights into long-sought phenomena in high-energy physics. Recently, theorists predicted new types of fermionic excitations in condensed-matter systems without any high-energy counterpart, and their existence is protected by crystalline symmetries. By studying the topology of the electronic structure in PdBiSe using density functional theory calculations and bulk-sensitive soft x-ray angle-resolved photoemission spectroscopy, we demonstrate a coexistence of four different types of topological fermions: Weyl, Rarita-Schwinger-Weyl, double class-II three-component, and charge-2 fourfold fermions. Our discovery provides a remarkable platform to realize multiple fermions in a single solid, charting the way forward to studies of their potentially exotic properties as well as their interplay.
TL;DR: A review of the most recent direct searches for supersymmetry developed by the ATLAS and CMS collaborations at the Large Hadron Collider can be found in this paper, where a supersymmetric model is proposed.
03 Oct 2019
TL;DR: The present study aims to present in an original vision the structure of the nuclear particles and their dimensions, with the possibility of their dynamic determination, depending on the energy of the respective moving particles.
Abstract: To better understand the structure of matter, it is not enough to study atoms and molecules. For living matter, it is necessary to study the cell, including the mitochondrial, and for matter in general, it is necessary to determine the elemental elements of the atom, and further those of the nucleus, how the nucleons bind to each other, forming virtually new atomic structures if they have electrons, or new ionic structures if they suffer a lack of electrons. The present study aims to present in an original vision the structure of the nuclear particles and their dimensions, with the possibility of their dynamic determination, depending on the energy of the respective moving particles. The basic idea of the theoretical study is that an elementary particle in motion changes its dimensions according to its linear displacement velocity. The originality of the study consists in using the total kinetic energy of a moving mechanical particle, the energy constituted by the sum of kinetic energy at translation and that of the kinetic energy of rotation around a particle’s own axis. The most important application of the theory presented is the determination of the dimensions and structure of the elementary nuclear particles in order to understand the nuclear phenomena of the nucleus and of the nuclei particles of an atom.
TL;DR: In this paper, the relativistic coupled cluster calculations of the nuclear MQM interaction constants in BaF, YbF, BaOH, and YbOH were presented.
Abstract: Nuclear magnetic quadrupole moments (MQMs), like intrinsic electric dipole moments of elementary particles, violate both parity and time-reversal symmetry and therefore probe physics beyond the Standard Model of particle physics. We report on accurate relativistic coupled cluster calculations of the nuclear MQM interaction constants in BaF, YbF, BaOH, and YbOH. We elaborate on estimates of the uncertainty of our results. The implications of experiments searching for nonzero nuclear MQMs are discussed.
TL;DR: Several models of dark matter are discussed, predicting new colored, hyper-colored or techni-colored particles and their accelerator and non-accelerator probes and the nontrivial properties of the proposed dark matter candidates can shed new light on the dark matter physics.
Abstract: The problems of simple elementary weakly interacting massive particles (WIMPs) appeal to extend the physical basis for nonbaryonic dark matter. Such extension involves more sophisticated dark matter candidates from physics beyond the Standard Model (BSM) of elementary particles. We discuss several models of dark matter, predicting new colored, hyper-colored or techni-colored particles and their accelerator and non-accelerator probes. The nontrivial properties of the proposed dark matter candidates can shed new light on the dark matter physics. They provide interesting solutions for the puzzles of direct and indirect dark matter search.
TL;DR: The results are interpreted using simplified models of dark matter production via spin-0 mediators that couple to dark matter particles and to standard model quarks, providing constraints on the coupling strength between the mediator and the quarks.
Abstract: A search is performed for dark matter particles produced in association with a top quark pair in proton-proton collisions at root s = 13 TeV. The data correspond to an integrated luminosity of 35.9 fb(-1) recorded by the CMS detector at the LHC. No significant excess over the standard model expectation is observed. The results are interpreted using simplified models of dark matter production via spin-0 mediators that couple to dark matter particles and to standard model quarks, providing constraints on the coupling strength between the mediator and the quarks. These are the most stringent collider limits to date for scalar mediators, and the most stringent for pseudoscalar mediators at low masses.
TL;DR: In this paper, the authors systematically study scenarios for multi-component dark matter based on various $Z_N$ symmetries and with different sets of scalar fields charged under it.
Abstract: The dark matter may consist not of one elementary particle but of different species, each of them contributing a fraction of the observed dark matter density. A major theoretical difficulty with this scenario --dubbed multi-component dark matter-- is to explain the stability of these distinct particles. Imposing a single $Z_N$ symmetry, which may be a remnant of a spontaneously broken $U(1)$ gauge symmetry, seems to be the simplest way to simultaneously stabilize several dark matter particles. In this paper we systematically study scenarios for multi-component dark matter based on various $Z_N$ symmetries ($N\leq 10$) and with different sets of scalar fields charged under it. A generic feature of these scenarios is that the number of stable particles is not determined by the Lagrangian but depends on the relations among the masses of the different fields charged under the $Z_N$ symmetry. We explicitly obtain and illustrate the regions of parameter space that are consistent with up to five dark matter particles. For $N$ odd, all these particles turn out to be complex, whereas for $N$ even one of them may be real. Within this framework, many new models for multi-component dark matter can be implemented.
Posted Content•
TL;DR: The electron and positron magnetic moments are the most precise prediction of the standard model of particle physics as mentioned in this paper, and the most accurate measurement of a property of an elementary particle has been made to test this result.
Abstract: The electron and positron magnetic moments are the most precise prediction of the standard model of particle physics. The most accurate measurement of a property of an elementary particle has been made to test this result. A new experimental method is now being employed in an attempt to improve the measurement accuracy by an order of magnitude. Positrons from a "student source" now suffice for the experiment. Progress toward a new measurement is summarized.
TL;DR: In this paper, the role of the Yang-Mills Higgs interaction plays at fixing the gauge for the Higgs field, in order to sustain a homogeneous and isotropic background, and at driving the late accelerated expansion of the Universe by moving the field away of the minimum of its potential and holding it towards an asymptotic finite value.
Abstract: Inspired in the Standard Model of Elementary Particles, the Einstein Yang-Mills Higgs action with the Higgs field in the SU(2) representation was proposed in Class. Quantum Grav. 32 (2015) 045002 as the element responsible for the dark energy phenomenon. We revisit this action emphasizing in a very important aspect not sufficiently explored in the original work and that substantially changes its conclusions. This aspect is the role that the Yang-Mills Higgs interaction plays at fixing the gauge for the Higgs field, in order to sustain a homogeneous and isotropic background, and at driving the late accelerated expansion of the Universe by moving the Higgs field away of the minimum of its potential and holding it towards an asymptotic finite value. We analyse the dynamical behaviour of this system and supplement this analysis with a numerical solution whose initial conditions are in agreement with the current observed values for the density parameters. This scenario represents a step towards a successful merging of cosmology and well-tested particle physics phenomenology.
TL;DR: In this article, the authors discuss several models of dark matter, predicting new colored, hyper-colored or techni-colored particles and their accelerator and non-accelerator probes.
Abstract: The problems of simple elementary weakly interacting massive particles (WIMPs) appeal to extend the physical basis for nonbaryonic dark matter. Such extension involves more sophisticated dark matter candidates from physics beyond the Standard Model (BSM) of elementary particles. We discuss several models of dark matter, predicting new colored, hyper-colored or techni-colored particles and their accelerator and non-accelerator probes. The nontrivial properties of the proposed dark matter candidates can shed new light on the dark matter physics. They provide interesting solutions for the puzzles of direct and indirect dark matter search.
01 Jan 2019
TL;DR: In this paper, the authors consider the unitary Abelian Higgs model and investigate its spectral functions at one-loop order, which allows them to disentangle what is physical and what is not at the level of the elementary particle propagators, in conjunction with the Nielsen identities.
Abstract: We consider the unitary Abelian Higgs model and investigate its spectral functions at one-loop order. This analysis allows us to disentangle what is physical and what is not at the level of the elementary particle propagators, in conjunction with the Nielsen identities. We highlight the role of the tadpole graphs and the gauge choices to get sensible results. We also introduce an Abelian Curci-Ferrari action coupled to a scalar field to model a massive photon which, like the non-Abelian Curci-Ferarri model, is left invariant by a modified non-nilpotent BRST symmetry. We clearly illustrate its nonunitary nature directly from the spectral function viewpoint. This provides a functional analogue of the Ojima observation in the canonical formalism: there are ghost states with nonzero norm in the BRST-invariant states of the Curci-Ferrari model.
TL;DR: In this article, a topological model for elementary particles based on 3-manifolds is described, where fermions are represented as hyperbolic knot complements and bosons as torus bundles.
Abstract: In this paper, we will describe a topological model for elementary particles based on 3-manifolds. Here, we will use Thurston’s geometrization theorem to get a simple picture: fermions as hyperbolic knot complements (a complement C ( K ) = S 3 \ ( K × D 2 ) of a knot K carrying a hyperbolic geometry) and bosons as torus bundles. In particular, hyperbolic 3-manifolds have a close connection to number theory (Bloch group, algebraic K-theory, quaternionic trace fields), which will be used in the description of fermions. Here, we choose the description of 3-manifolds by branched covers. Every 3-manifold can be described by a 3-fold branched cover of S 3 branched along a knot. In case of knot complements, one will obtain a 3-fold branched cover of the 3-disk D 3 branched along a 3-braid or 3-braids describing fermions. The whole approach will uncover new symmetries as induced by quantum and discrete groups. Using the Drinfeld–Turaev quantization, we will also construct a quantization so that quantum states correspond to knots. Particle properties like the electric charge must be expressed by topology, and we will obtain the right spectrum of possible values. Finally, we will get a connection to recent models of Furey, Stoica and Gresnigt using octonionic and quaternionic algebras with relations to 3-braids (Bilson–Thompson model).
TL;DR: In this paper, the authors used lattice gauge theory to study the physical weak vector bosons off shell, especially their form factor and weak radius, and compared the results to the ones for the elementary particles.
Abstract: Gauge invariance requires even in the weak interactions that physical, observable particles are described by gauge-invariant composite operators. Such operators have the same structure as those describing bound states, and consequently the physical versions of the ${W}^{\ifmmode\pm\else\textpm\fi{}}$, the $Z$, and the Higgs should have some kind of substructure. To test this consequence, we use lattice gauge theory to study the physical weak vector bosons off shell, especially their form factor and weak radius, and compare the results to the ones for the elementary particles. We find that the physical particles show substantial deviations from the structure of a pointlike particle. At the same time the gauge-dependent elementary particles exhibit unphysical behavior.
TL;DR: In this article, the sensitivity of the proposed compact linear collider (CLIC) to the existence of beyond the standard model (SM) Higgs bosons through their decays into pairs of massive gauge bosons was analyzed.
Abstract: We analyse the sensitivity of the proposed compact linear collider (CLIC) to the existence of beyond the standard model (SM) Higgs bosons through their decays into pairs of massive gauge bosons $$H \rightarrow VV$$
and SM-like Higgses $$H \rightarrow hh$$
, considering CLIC centre of mass energies $$\sqrt{s} = 1.4$$
TeV and 3 TeV. We find that resonant di-Higgs searches at CLIC would allow for up to two orders of magnitude improvement w.r.t. the sensitivity achievable by HL-LHC in the mass range $$m_H \in [250\,\mathrm {GeV},\, 1 \,\mathrm {TeV}]$$
. Focusing then on a real singlet extension of the SM, we explore the prospects of heavy Higgs searches at CLIC for probing the regions of parameter space yielding a strongly first order electroweak phase transition that could generate the observed matter-antimatter asymmetry of the Universe. Our study illustrates the complementarity between CLIC and other possible future colliders like FCC-ee in probing singlet extensions of the SM, and shows that high-energy $$e^+ e^-$$
colliders provide a powerful means to unravel the nature of electroweak symmetry breaking in the early Universe.
TL;DR: In this article, the anomalous magnetic moment and electric dipole moment (EDM) were used to study the exotic spin-dependent interactions for muons and electrons, and a constraint for the scalar-pseudo-scalar (SP) type interaction at the interested range was obtained.
Abstract: Many experiments have been performed to search for the exotic spin-dependent interactions in ranges from $$\sim \upmu $$m to astrophysical range which corresponds to the energy scale of less than $$\sim $$10 eV. At present, nearly all known experiments searching for these new interactions at the macroscopic range are for protons, neutrons, and electrons. Constraints at this range for other fermions such as muons are scarce, though muons might be the most suspicious particles which might take part in new interactions, considering their involvement of several well-known puzzles of modern physics. We use the anomalous magnetic moment and electric dipole moment (EDM) to study the exotic spin-dependent interactions for muons and electrons. The muon’s magnetic moment might indicate existing of the pseudo-scalar–pseudo-scalar (PP) type interaction. We set up a constraint for the scalar–pseudo-scalar (SP) type interaction at the interested range for muons. For the PP type interaction of electrons, we obtained a new constraint at the range of $$\sim $$ nm to $$\sim $$ 1 mm. Since all the present experiments searching for the new forces give zero results, it is reasonable to consider that these new interactions might only couple to muons. We propose to further search for the new interactions using the muon spin rotation techniques.
23 May 2019
TL;DR: In this paper, the authors employ holography to analyze the role of the critical point on far-from-equilibrium dynamics of strongly coupled plasmas and show that it affects the time it takes for a strongly coupled plasma to display hydrodynamic behavior.
Abstract: Quantum Chromodynamics (QCD) is the fundamental theory that governs the strong interaction, whose fundamental particles are quarks and gluons. In terms of energy scales, QCD is characterized by asymptotic freedom (approximately free quarks and gluons) and color confinement (quarks and gluons confined inside hadrons), where the former can be treated perturbatively and the latter is an intrinsic non-perturbative phenomenon. At finite temperature, hadronic matter undergoes a crossover phase transition from a gas of hadrons to the quark-gluon plasma (QGP) as the temperature increases. Near the crossover, where hadrons ``melt'' to release quarks and gluons, QCD is in its non-perturbative regime and the QGP is strongly coupled, posing great challenges for analytical studies. The so-called AdS/CFT duality, also known as holography, comes to offer a unique opportunity to study the QGP by providing a map between strongly coupled theories (which are generally very hard to solve) and a classical theory of gravity. On the experimental front, the study of the QGP is carried out in particle accelerators by colliding ultrarelativistic heavy ions. In these experiments, the QGP created undergoes rapid expansion and there is a very intricate interplay between soft and hard scales, from initial conditions to final the stream of particles. This scenario makes it evident that one must understand the QGP also out of equilibrium. Fortunately, holography is well suited for this task. By solving the time dependent Einstein's equations, using general techniques previously employed in numerical general relativity, one can study non-equilibrium phenomena of strongly coupled plasmas. Furthermore, the QCD phase diagram on the (T,mu_B) plane, where T is the temperature and mu_B the baryon chemical potential, remains largely unknown due to its non-perturbative aspects. In particular, it is conjectured the existence of a critical point delimiting the crossover region from the first order phase transition. Motivated by these facts, this thesis employs holography to analyze the role of the critical point on far-from-equilibrium dynamics. For instance, it is investigated how the critical point affects the time that it takes for a strongly coupled plasma to display hydrodynamic behavior starting from a far-from-equilibrium initial state.
TL;DR: Using lattice simulations, it is demonstrated from first principles the existence of a nonperturbative mechanism for elementary particle mass generation in models with gauge fields, fermions, and scalars, if an exact invariance forbids power divergent fermion masses and fermionic chiral symmetries broken at UV scale are maximally restored.
Abstract: Using lattice simulations we demonstrate from first principles the existence of a nonperturbative mechanism for elementary particle mass generation in models with gauge fields, fermions, and scalars, if an exact invariance forbids power divergent fermion masses and fermionic chiral symmetries broken at UV scale are maximally restored. We show that in the Nambu-Goldstone phase a fermion mass term, unrelated to the Yukawa operator, is dynamically generated. In models with electroweak interactions weak boson masses are also generated, opening new scenarios for beyond the standard model physics.