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 $SU(3)_C \times U(1)_{\rm EM}$ is investigated. Spontaneous symmetry breaking of $U(1)_{\rm EM}$ at the temperature of the Universe today is carried out. The charged scalar field $\phi_{\rm EM}$ which breaks the symmetry is found to be ruled out for the charge of the electron, $q=e$. Scalar fields with millicharges are viable and limits on their masses and charges are found to be $q\lesssim10^{-3}e$ and $m_{\phi_{\rm EM}}\lesssim10^{-5} \rm eV$. Furthermore, it is possible that $U(1)_{\rm EM}$ has already been broken at temperatures higher than $T=2.7K$ given the nonzero limits on the mass of the photon. A photon mass of $m_{\gamma}=10^{-18} \rm eV$, the current upper limit, is found to require a spontaneously symmetry breaking scalar mass of $m_{\phi_{\rm EM}}\sim 10^{-13} \rm eV$ with charge $q=10^{-6}e$, well within the allowed parameter space of the model. Finally, the cosmological fate of the strong interaction is studied. $SU(3)_C$ is tested for complementarity in which the confinement phase of QCD $+$ colored scalars is equivalent to a spontaneously broken $SU(3)$ gauge theory. If complementarity is not applicable, $SU(3)_C$ 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 $SU(3)_C$ is left open. Cosmological implications for the metastability of the vacua - electromagnetic, color and electroweak - are discussed.

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 SU(3)C×U(1)EM is investigated. Spontaneous symmetry breaking of U(1)EM at the temperature of the Universe today is carried out. The charged scalar field φEM which breaks the symmetry is found to be ruled out for the charge of the electron, q=e. Scalar fields with millicharges are viable and limits on their masses and charges are found to be q10-3e and mφEM10-5 eV. Furthermore, it is possible that U(1)EM has already been broken at temperatures higher than T=2.7 K given the nonzero limits on the mass of the photon. A photon mass of mγ=10-18 eV, the current upper limit, is found to require a spontaneous symmetry breaking scalar mass of mφEM∼10-13 eV with charge q=10-6e, well within the allowed parameter space of the model. Finally, the cosmological fate of the strong interaction is studied. SU(3)C is tested for complementarity in which the confinement phase of QCD+ colored scalars is equivalent to a spontaneously broken SU(3) gauge theory. If complementarity is not applicable, SU(3)C 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 SU(3)C is left open. Cosmological implications for the metastability of the vacua - electromagnetic, color, and electroweak - are discussed.

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.

We propose a theory in which the Standard Model gauge symmetry is extended by a new SU(2) group acting nontrivially on the lepton sector which is spontaneously broken at the TeV scale. Under this SU(2) 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 U(1)χ 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 SU(2) instantons during a first order phase transition in the early Universe.

Recent observations of the angular correlation spectra in the decays $ {\rm ^4He}^*\to {\rm ^4He}+ e^+e^-$ and $ {\rm ^8Be}^*\to {\rm ^8Be}+ e^+e^-$ 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 $\sim 17$ MeV. In this work, we present a calculation of the invariant $m_{e^+e^-}$ 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 $e^+ e^-$ pair created by a new electromagnetic decay of $\rm ^4He$ caused by a proposed 12-quark hidden-color Fock state in the ${\rm {^4He}}$ nuclear wavefunction, the "hexadiquark.'' We find that we can fit the shape of the signal with the QCD Fock state at excitation energy ${\rm E^*}\simeq 17.9 $ 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 ${\rm ^4He}$.

Hidden-color configurations are a key prediction of QCD with important physical consequences. In this work we examine a QCD color-singlet configuration in nuclei formed by combining six scalar [ud] diquarks in a strongly bound SU(3)C channel. The resulting hexadiquark state is a charge-2, spin-0, baryon number-4, isospin-0, color-singlet state. It contributes to alpha clustering in light nuclei and to the additional binding energy not saturated by ordinary nuclear forces in He4 as well as the alpha-nuclei sequence of interest for nuclear astrophysics. We show that the strongly bound combination of six scalar isospin-0 [ud] diquarks within the nuclear wave function - relative to free nucleons - provides a natural explanation of the EMC effect measured by the CLAS collaboration's comparison of nuclear parton distribution function ratios for a large range of nuclei. These experiments confirmed that the EMC effect; i.e., the distortion of quark distributions within nuclei, is dominantly identified with the dynamics of neutron-proton (“isophobic”) short-range correlations within the nuclear wave function rather than proton-proton or neutron-neutron correlations.

A nuclear physics example of statistical bootstrap is used on the MARATHON nucleon structure function ratio data in the quark momentum fraction regions xB→0 and xB→1. The extrapolated F2 ratio as quark momentum fraction xB→1 is F2nF2p→0.4±0.05 and this value is compared to theoretical predictions. The extrapolated ratio when xB→0 favors the simple model of isospin symmetry with the complete dominance of sea quarks at low momentum fraction. At high-xB, the proton quark distribution function ratio d/u is derived from the F2 ratio and found to be d/u→1/6. Our extrapolated values for both the F2nF2p ratio and the d/u parton distribution function ratio are within uncertainties of perturbative QCD values from quark counting, helicity conservation arguments, and a Dyson-Schwinger equation with a contact interaction model. In addition, it is possible to match the statistical bootstrap value to theoretical predictions by allowing two compatible models to act simultaneously in the nucleon wave function. One such example is nucleon wave functions composed of a linear combination of a quark-diquark state and a three-valence quark correlated state with coefficients that combine to give the extrapolated F2 ratio at xB=1.

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 n and p nucleons in nuclear wavefunctions that are much stronger compared to p−p or n−n 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 A of high energy He4 nuclei to pairs of nucleons n and p with high relative transverse momentum, α+A→n+p+A′+X. The comparison of n−p events with p−p and n−n 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 [ud] diquarks.

The effective quantum field theory description of gravity, despite its non-renormalizability, allows for predictions beyond classical general relativity. As we enter the age of gravitational wave astronomy, an important and timely question is whether measurable quantum predictions that depart from classical gravity, analogous to quantum optics effects which cannot be explained by classical electrodynamics, can be found. In this work, we investigate quantum signatures in gravitational waves using tools from quantum optics. Squeezed-coherent gravitational waves, which can exhibit sub-Poissonian graviton statistics, can enhance or suppress the signal measured by an interferometer, a characteristic effect of quantum squeezing. Moreover, we show that Gaussian gravitational wave quantum states can be reconstructed from measurements over an ensemble of optical fields interacting with a single copy of the gravitational wave, thus opening the possibility of detecting quantum features of gravity beyond classical general relativity.