Nucleation at Finite Temperature: A Gauge-Invariant Perturbative Framework

We present a gauge-invariant framework for bubble nucleation in theories with radiative symmetry breaking at high temperature. As a procedure, this perturbative framework establishes a practical, gauge-invariant computation of the leading order nucleation rate, based on a consistent power counting in the high-temperature expansion. In model building and particle phenomenology, this framework has applications such as the computation of the bubble nucleation temperature and the rate for electroweak baryogenesis and gravitational wave signals from cosmic phase transitions.

Detection of early-universe gravitational-wave signatures and fundamental physics

Detection of a gravitational-wave signal of non-astrophysical origin would be a landmark discovery, potentially providing a significant clue to some of our most basic, big-picture scientific questions about the Universe. In this white paper, we survey the leading early-Universe mechanisms that may produce a detectable signal-including inflation, phase transitions, topological defects, as well as primordial black holes-and highlight the connections to fundamental physics. We review the complementarity with collider searches for new physics, and multimessenger probes of the large-scale structure of the Universe.

Thermodynamics of a Two-Step Electroweak Phase Transition

New field content beyond that of the standard model of particle physics can alter the thermal history of electroweak symmetry breaking in the early Universe. In particular, the symmetry breaking may have occurred through a sequence of successive phase transitions. We study the thermodynamics of such a scenario in a real triplet extension of the standard model, using nonperturbative lattice simulations. Two-step electroweak phase transition is found to occur in a narrow region of allowed parameter space with the second transition always being first order. The first transition into the phase of nonvanishing triplet vacuum expectation value is first order in a non-negligible portion of the two-step parameter space. A comparison with two-loop perturbative calculation is provided and significant discrepancies with the nonperturbative results are identified.

Left-Right Symmetry and Leading Contributions to Neutrinoless Double Beta Decay

We study the impact of the mixing (LR mixing) between the standard model W boson and its hypothetical, heavier right-handed parter W_{R} on the neutrinoless double beta decay (0νββ decay) rate. Our study is done in the minimal left-right symmetric model assuming a type-II dominance scenario with charge conjugation as the left-right symmetry. We then show that the 0νββ decay rate may be dominated by the contribution proportional to this LR mixing, which at the hadronic level induces the leading-order contribution to the interaction between two pions and two charged leptons. The resulting long-range pion exchange contribution can significantly enhance the decay rate compared to previously considered short-range contributions. Finally, we find that even if future cosmological experiments rule out the inverted hierarchy for neutrino masses, there are still good prospects for a positive signal in the next generation of 0νββ decay experiments.

Parity-Violating Møller Scattering at Next-to-Next-to-Leading Order: Closed Fermion Loops

A complete, gauge-invariant computation of two-loop virtual corrections involving closed fermion loops to the polarized Møller scattering asymmetry is presented. The set of contributions involving two closed fermion loops and the set involving one closed fermion loop are numerically similar in magnitude to the one-loop bosonic corrections and yield an overall correction of 1.3% relative to the tree level asymmetry. We estimate sizes of the remaining two-loop contributions and discuss implications for the upcoming MOLLER (Measurement of a Lepton-Lepton Electroweak Reaction) experiment.

Reduced Hadronic Uncertainty in the Determination of V_{ud}

We analyze the universal radiative correction Δ_{R}^{V} to neutron and superallowed nuclear β decay by expressing the hadronic γW-box contribution in terms of a dispersion relation, which we identify as an integral over the first Nachtmann moment of the γW interference structure function F_{3}^{(0)}. By connecting the needed input to existing data on neutrino and antineutrino scattering, we obtain an updated value of Δ_{R}^{V}=0.02467(22), wherein the hadronic uncertainty is reduced. Assuming other standard model theoretical calculations and experimental measurements remain unchanged, we obtain an updated value of |V_{ud}|=0.97370(14), raising tension with the first row Cabibbo-Kobayashi-Maskawa unitarity constraint. We comment on ways current and future experiments can provide input to our dispersive analysis.

Electroweak beautygenesis: from b→s CP violation to the cosmic baryon asymmetry

We address the possibility that CP violation in B(s)-B(s) mixing may help explain the origin of the cosmic baryon asymmetry. We propose a new baryogenesis mechanism--"electroweak beautygenesis"--explicitly showing that these two CP-violating phenomena can be sourced by a common CP phase. As an illustration, we work in the two-Higgs-doublet model. Because the relevant CP phase is flavor off diagonal, this mechanism is less severely constrained by null results of electric dipole moment searches than other scenarios. We show how measurements of flavor observables by the D0, CDF, and LHCb collaborations test this scenario.

Dark-matter-induced violation of the weak equivalence principle

A long-range fifth force coupled to dark matter can induce a coupling to ordinary matter if the dark matter interacts with standard model fields. We consider constraints on such a scenario from both astrophysical observations and laboratory experiments. We also examine the case where the dark matter is a weakly interacting massive particle, and derive relations between the coupling to dark matter and the coupling to ordinary matter for different models. Currently, this scenario is most tightly constrained by galactic dynamics, but improvements in Eötvös experiments can probe unconstrained regions of parameter space.

Yukawa interactions and supersymmetric electroweak baryogenesis

We analyze the quantum transport equations for supersymmetric electroweak baryogenesis including previously neglected bottom and tau Yukawa interactions and show that they imply the presence of a previously unrecognized dependence of the cosmic baryon asymmetry on the spectrum of third generation quark and lepton superpartners. For fixed values of the CP-violating phases in the supersymmetric theory, the baryon asymmetry can vary in both magnitude and sign as a result of the squark and slepton mass dependence. For light, right-handed top and bottom quark superpartners, the baryon number creation can be driven primarily by interactions involving third generation leptons and their superpartners.

How Magnetic is the Dirac Neutrino?

We derive model-independent, "naturalness" upper bounds on the magnetic moments munu of Dirac neutrinos generated by physics above the scale of electroweak symmetry breaking. In the absence of fine-tuning of effective operator coefficients, we find that current information on neutrino mass implies that[EQUATION: SEE TEXT] bohr magnetons. This bound is several orders of magnitude stronger than those obtained from analyses of solar and reactor neutrino data and astrophysical observations.

Neutrinoless double Beta decay and lepton flavor violation

We point out that extensions of the standard model with low scale (approximately TeV) lepton number violation (LNV) generally lead to a pattern of lepton flavor violation (LFV) experimentally distinguishable from the one implied by models with grand unified theory scale LNV. As a consequence, muon LFV processes provide a powerful diagnostic tool to determine whether or not the effective neutrino mass can be deduced from the rate of neutrinoless double beta decay. We discuss the role of mu-->egamma and mu-->e conversion in nuclei, which will be studied with high sensitivity in forthcoming experiments.

Hadronic light-by-light contribution to muon g - 2 in chiral perturbation theory

We compute the hadronic light-by-light scattering contributions to the muon anomalous magnetic moment, a(LL)(mu)(had), in chiral perturbation theory that are enhanced by large logarithms and a factor of N(C). They depend on a low-energy constant constrained by eta-->mu(+) mu(-) and pi(0)-->e(+)e(-) branching ratios. However, the dependence of a(LL)(mu)(had) on nonlogarithmically enhanced effects cannot be constrained except through the measurement of the anomalous moment itself.

Charged current universality in the minimal supersymmetric standard model

We compute the complete one-loop contributions to low-energy charged current weak interaction observables in the minimal supersymmetric standard model (MSSM). We obtain the constraints on the MSSM parameter space which arise when precision low-energy charged current data are analyzed in tandem with measurements of the muon anomaly. While the data allow the presence of at least one light neutralino, they also imply a pattern of mass splittings among first and second generation sleptons and squarks which contradicts predictions of widely used models for supersymmetry-breaking mediation.

Parity-violating photoproduction of pi(+/-) on the delta resonance

We analyze the real-photon asymmetry A(gamma)(+/-) for the parity-violating (PV) pi(+/-) production on the Delta resonance via the reactions (-->)gamma + p --> Delta(+) --> pi(+) + n and (-->)gamma + d --> Delta(0) + p --> pi(-) + p + p. This asymmetry is nonvanishing due to a PV gamma N Delta coupling constant, d(Delta)(+/-). We argue that an experimental determination of this coupling would be of interest for hadron dynamics, possibly shedding light on the S-wave/ P-wave puzzle in the hyperon nonleptonic decays and the violation of Hara's theorem in weak radiative hyperon decays.

Anapole moment and other constraints on the strangeness conserving Hadronic weak interaction

Standard analyses of low-energy NN and nuclear parity-violating observables have been based on a pi-, rho-, and omega-exchange model capable of describing all five independent s-p partial waves. Here a parallel analysis is performed for the one-body, exchange-current, and nuclear polarization contributions to the anapole moments of 133Cs and 205Tl. The resulting constraints are not consistent, though there remains some degree of uncertainty in the nuclear structure analysis of the atomic moments.