24 research outputs found
Millicharged Scalar Fields, Massive Photons and the Breaking of
Under the assumption that the current epoch of the Universe is not special,
i.e. is not the final state of a long history of processes in particle physics,
the cosmological fate of is investigated.
Spontaneous symmetry breaking of at the temperature of the
Universe today is carried out. The charged scalar field which
breaks the symmetry is found to be ruled out for the charge of the electron,
. Scalar fields with millicharges are viable and limits on their masses
and charges are found to be and . Furthermore, it is possible that
has already been broken at temperatures higher than given the nonzero
limits on the mass of the photon. A photon mass of , the current upper limit, is found to require a spontaneously symmetry
breaking scalar mass of with charge
, well within the allowed parameter space of the model. Finally,
the cosmological fate of the strong interaction is studied. is tested
for complementarity in which the confinement phase of QCD colored scalars
is equivalent to a spontaneously broken gauge theory. If
complementarity is not applicable, has multiple symmetry breaking
paths with various final symmetry structures. The stability of the colored
vacuum at finite temperature in this scenario is nonperturbative and a
definitive statement on the fate of is left open. Cosmological
implications for the metastability of the vacua - electromagnetic, color and
electroweak - are discussed.Comment: 7 pages. Version accepted for publication in PR
Asymmetric Dark Matter and Baryogenesis from
We propose a theory in which the Standard Model gauge symmetry is extended by
a new group acting nontrivially on the lepton sector which is
spontaneously broken at the TeV scale. Under this the ordinary
leptons form doublets along with new lepton partner fields. This construction
naturally contains a dark matter candidate, the partner of the right-handed
neutrino, stabilized by a residual global symmetry. We show that
one can explain baryogenesis through an asymmetric dark matter scenario, in
which generation of related asymmetries in the dark matter and baryon sectors
is driven by the instantons during a first order phase transition
in the early universe.Comment: Version accepted for publication in Physical Review D. 11 pages, 4
figures. References added, minor change
Quantum Chromodynamics Resolution of the ATOMKI Anomaly in Nuclear Transitions
Recent observations of the angular correlation spectra in the decays and have
been suggested as due to the creation and subsequent decay to an
electron-positron pair of a new light particle with a mass of MeV. In
this work, we present a calculation of the invariant mass spectrum
of the electromagnetic transition of an excited state of helium and estimate
the differential and total width of the decay. We investigate the possibility
that the source of the signal is an pair created by a new
electromagnetic decay of caused by a proposed 12-quark hidden-color
Fock state in the nuclear wavefunction, the "hexadiquark.'' We
find that we can fit the shape of the signal with the QCD Fock state at
excitation energy MeV and a Gaussian form factor for
the electromagnetic decay. We address the physical issues with the fit
parameters using properties of the hexadiquark state. In light of this work, we
emphasize the need for independent experimental confirmation or refutation of
the ATOMKI results as well as further experiments to detect the proposed new
excitation of .Comment: Condensed version, 8 pages, 3 figures, comments welcom
Physical Implications of the Extrapolation and Statistical Bootstrap of the Nucleon Structure Function Ratio for Mirror Nuclei He and H}
A nuclear physics example of statistical bootstrap is used on the MARATHON
data nucleon structure function ratio, , in the quark
momentum fraction and regions. The
extrapolated ratio value as quark momentum fraction
approaches 0.4 and this value is compared to theoretical predictions. The
extrapolated ratio when favors the simple model of isospin
symmetry with the complete dominance of seaquarks at low momentum fraction. At
high-, the proton quark distribution function ratio is derived from
the ratio and found to be
. Our extrapolated values for both the
ratio and the parton distribution function ratio
most closely match perturbative QCD values from quark counting and helicity
conservation arguments but still differ by roughly . The mismatch to
theoretical predictions may be ameliorated if two compatible models act
simultaneously in the nucleon wavefunction. One such example is nucleon
wavefunctions composed of a linear combination of a quark-diquark state and a
3-valence quark correlated state with coefficients that combine to give the
extrapolated ratio of
Searching for an Enhanced Signal of the Onset of Color Transparency in Baryons with D(e,e′p)n Scattering
Observation of the onset of color transparency in baryons would provide a new means of studying the nuclear strong force and would be the first clear evidence of baryons transforming into a color-neutral point-like size in the nucleus as predicted by quantum chromodynamics. Recent C (e, e′p) results from electron-scattering did not observe the onset of color transparency (CT) in protons up to spacelike four-momentum transfers squared, Q2 = 14.2 GeV 2 . The traditional methods of searching for CT in (e, e′p) scattering use heavy targets favoring kinematics with already initially reduced final state interactions (FSIs) such that any CT effect that further reduces FSIs will be small. The reasoning behind this choice is the difficulty in accounting for all FSIs. D (e, e′p)η , on the other hand, has well-understood FSI contributions from double scattering with a known dependence on the kinematics and can show an increased sensitivity to hadrons in point-like configurations. Double scattering is the square of the re-scattering amplitude in which the knocked-out nucleon interacts with the spectator nucleon, a process that is suppressed in the presence of point-like configurations and is particularly well-studied for the deuteron. This suppression yields a quadratic sensitivity to CT effects and is strongly dependent on the choice of kinematics. Here, we describe a possible Jefferson National Accelerator Facility (JLab) electron-scattering experiment that utilizes these kinematics and explores the potential signal for the onset of CT with enhanced sensitivity as compared to recent experiments
Diffractive Dissociation of Alpha Particles as a Test of Isophobic Short-Range Correlations inside Nuclei
The CLAS collaboration at Jefferson Laboratory has compared nuclear parton
distributions for a range of nuclear targets and found that the EMC effect
measured in deep inelastic lepton-nucleus scattering has a strongly "isophobic"
nature. This surprising observation suggests short-range correlations between
neighboring and nucleons in nuclear wavefunctions that are much
stronger compared to or correlations. In this paper we propose a
definitive experimental test of the nucleon-nucleon explanation of the
isophobic nature of the EMC effect: the diffractive dissociation on a nuclear
target of high energy nuclei to pairs of nucleons and
with high relative transverse momentum, . The
comparison of events with and events directly tests the
postulated breaking of isospin symmetry. The experiment also tests alternative
QCD-level explanations for the isophobic EMC effect. In particular it will test
a proposal for hidden-color degrees of freedom in nuclear wavefunctions based
on isospin-zero diquarks.Comment: 5 pages, references added, clarifications due to helpful referee
comments (latexdiff for all changes). Accepted for publication in Physics
Letters
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Symmetries, Dark Matter and Minicharged Particles
This theoretical particle physics thesis is an investigation into old and new symmetries of Nature. Known symmetries and conservation laws serve as a guide for dark and visible sector model building. New symmetries of Nature are proposed, broken and subsequently reinstated at high temperatures in order to discover well motivated particle physics models for cosmological observations implying the existence of a dark sector. Candidate processes for creation of a non-primordial matter/antimatter asymmetry result from out of equilibrium spontaneous breaking of these symmetries in the early Universe. Using the Standard Model of particle physics as a foundation with minimal new degrees of freedom, minicharged and millicharged particles emerge from a proposed spontaneous breaking of known symmetries. Experimental predictions and constraints for such dark matter candidates are given briefly here and outlined for future work. Constraints on neutrino-like particles found in the debris of broken local (gauge) symmetries are given, a subset of which are sterile and appear to be viable particle dark matter candidates
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Diquark induced short-range nucleon-nucleon correlations & the EMC effect
Diquark formation across a short-range nucleon-nucleon pair is proposed as the underlying QCD physics of short-range correlations (SRC) in nuclei. SRC pairs have been proposed as the cause of distorted quark behavior in nuclei; experimentally observed quark momentum distribution distortions termed the EMC effect. The strong spatial overlap of SRC pairs brings nucleon constituents within range of inter-nucleon QCD potentials and any bonds formed - such as the diquark bond - affects their distributions. In this SRC model, diquarks form in the 3C⊗3C→3¯C channel of SU(3)C acting on valence quarks from highly overlapping nucleon wavefunctions. The most energetically favorable diquark is a valence u quark from one nucleon with a valence d quark from the other in a spin-0 state bound together via continual single gluon exchange and an attractive quantum chromodynamics short-range potential. Formation of a new scalar isospin-singlet [ud] diquark across a NN pair is proposed as the primary QCD-level theoretical foundation for SRC models of distorted structure functions in A≥3 nuclei. Contributions from the higher mass spin-1 isospin triplet states (ud), (uu) and (dd) are possible, with the spin-1 (ud) diquark proposed as a higher mass but viable structure function distortion mechanism for the spin-1 ground state deuteron. Predictions are made for lepton scattering experiments on H3 and He3 nuclear targets, with implications for the coefficients of the 3-valence quark Fock states in the nucleon wavefunction
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Strong Interaction Physics at the Luminosity Frontier with 22 GeV Electrons at Jefferson Lab
This document presents the initial scientific case for upgrading the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab (JLab) to 22 GeV. It is the result of a community effort, incorporating insights from a series of workshops conducted between March 2022 and April 2023. With a track record of over 25 years in delivering the world's most intense and precise multi-GeV electron beams, CEBAF's potential for a higher energy upgrade presents a unique opportunity for an innovative nuclear physics program, which seamlessly integrates a rich historical background with a promising future. The proposed physics program encompass a diverse range of investigations centered around the nonperturbative dynamics inherent in hadron structure and the exploration of strongly interacting systems. It builds upon the exceptional capabilities of CEBAF in high-luminosity operations, the availability of existing or planned Hall equipment, and recent advancements in accelerator technology. The proposed program cover various scientific topics, including Hadron Spectroscopy, Partonic Structure and Spin, Hadronization and Transverse Momentum, Spatial Structure, Mechanical Properties, Form Factors and Emergent Hadron Mass, Hadron-Quark Transition, and Nuclear Dynamics at Extreme Conditions, as well as QCD Confinement and Fundamental Symmetries. Each topic highlights the key measurements achievable at a 22 GeV CEBAF accelerator. Furthermore, this document outlines the significant physics outcomes and unique aspects of these programs that distinguish them from other existing or planned facilities. In summary, this document provides an exciting rationale for the energy upgrade of CEBAF to 22 GeV, outlining the transformative scientific potential that lies within reach, and the remarkable opportunities it offers for advancing our understanding of hadron physics and related fundamental phenomena