We investigate an extension of the Standard Model (SM) with a $U(1{)}^{\prime }$ gauge symmetry, which is spontaneously broken by a complex scalar singlet and where the new gauge boson is a stable dark matter candidate via a $Z_2$ flavor symmetry. The possibility of generating a strongly first order electroweak phase transition (EWPT) needed for the electroweak baryogenesis mechanism in this model is studied using a gauge-independent method. Our result shows a considerable parameter space where both successful dark matter phenomenologies and a strongly first order electroweak phase transition can be achieved.

We found a minimal and a comprehensive set of directly measurable quantities defining the most general two-Higgs-doublet model (2HDM); we call these quantities observables. The potential parameters of the model are expressed explicitly via these observables (plus nonphysical parameters which are similar to gauge parameters). The model with arbitrary values of these observables can, in principle, be realized (up to general enough limitations). Our results open the door for the study of Higgs models in terms of measurable quantities only. The experimental limitations can be implemented here directly, without complex, often model-dependent, analysis of the Lagrangian coefficients. The principal opportunity to determine all parameters of the 2HDM from the (future) data meets strong practical limitation. It is the problem for a very long time. Apart from this construction per se, we also obtain some by-products. Among them are the following: a simple criterium for charge parity symmetry ($CP$) conservation in the 2HDM, a new sum rules for Higgs couplings, a clear possibility of the coexistence of relatively light Higgses with the strong interaction in the Higgs sector, and a simple expression for the triple Higgs vertex $g(h_a{h}_a{h}_a)$, useful for the analysis of future $hhh$ coupling measurements.

Doubly charged excited leptons give rise to interesting signatures for physics beyond the standard model at the present Large Hadron Collider. These exotic states are introduced in extended isospin multiplets which couple to the ordinary leptons and quarks either with gauge or contact effective interactions or a combination of both. In this paper we study the production and the corresponding signatures of doubly charged leptons at the forthcoming linear colliders, and we focus on the electron-electron beam setting. In the framework of gauge interactions, the interference between the $t$ and $u$ channels is evaluated that has been neglected so far. A pure leptonic final state is considered ($e^{-}{e}^{-}\to e^{-}{e}^{-}{\nu }_e{\overline{\nu }}_e$) that experimentally translates into a like-sign dilepton and missing transverse energy signature. We focus on the standard model irreducible background, and we study the invariant like-sign dilepton mass distribution for both the signal and background processes. Finally, we provide the 3 and 5-sigma statistical significance exclusion curves in the model parameter space. We find that for a doubly charged lepton mass $m^{*}\approx 2\mathrm{TeV}$ the expected lower bound on the compositeness scale at Compact Linear Collider, $\mathrm{\Lambda }>25\mathrm{TeV}$, is much stronger than the current lower bound from the LHC ($\mathrm{\Lambda }>5\mathrm{TeV}$) and remains highly competitive with the bounds expected from run II of the LHC.

We study the breaking of rotational symmetry on the lattice for irreducible tensor operators and practical methods for suppressing such breaking. We illustrate the features of the general problem using an $\alpha$ cluster model for ${}^8\mathrm{Be}$. We focus on the lowest states with nonzero angular momentum and examine the matrix elements of multipole moment operators. We show that reduced matrix elements are well reproduced by averaging over all possible orientations of the quantum state. This averaging is performed in terms of a sum of matrix elements weighted by the Clebsch-Gordan coefficients of each orientation. For our $\alpha$ cluster model, we find that the effects of rotational symmetry breaking can be largely eliminated for lattice spacings of $a\le 1.7\mathrm{fm}$, and we expect similar improvement for lattice Monte Carlo calculations.

We present a lattice-QCD calculation of the $B\to \pi \ell \nu$ semileptonic form factors and a new determination of the CKM matrix element $|V_{ub}|$. We use the MILC asqtad ($2+1$)-flavor lattice configurations at four lattice spacings and light-quark masses down to $1/20$ of the physical strange-quark mass. We extrapolate the lattice form factors to the continuum using staggered chiral perturbation theory in the hard-pion and SU(2) limits. We employ a model-independent $z$ parametrization to extrapolate our lattice form factors from large-recoil momentum to the full kinematic range. We introduce a new functional method to propagate information from the chiral-continuum extrapolation to the $z$ expansion. We present our results together with a complete systematic error budget, including a covariance matrix to enable the combination of our form factors with other lattice-QCD and experimental results. To obtain $|V_{ub}|$, we simultaneously fit the experimental data for the $B\to \pi \ell \nu$ differential decay rate obtained by the BABAR and Belle collaborations together with our lattice form-factor results. We find $|V_{ub}|=(3.72\pm 0.16)\times {10}^{-3}$, where the error is from the combined fit to lattice plus experiments and includes all sources of uncertainty. Our form-factor results bring the QCD error on $|V_{ub}|$ to the same level as the experimental error. We also provide results for the $B\to \pi \ell \nu$ vector and scalar form factors obtained from the combined lattice and experiment fit, which are more precisely determined than from our lattice-QCD calculation alone. These results can be used in other phenomenological applications and to test other approaches to QCD.

We report on the first observations of ${\overline{B}}^0\to D_1(2430{)}^0\omega$, ${\overline{B}}^0\to D_1(2420{)}^0\omega$, and ${\overline{B}}^0\to D_2^{*}(2460{)}^0\omega$ decays. The ${\overline{B}}^0\to D^{*+}\rho (1450{)}^{-}$ decay is also observed. The branching fraction measurements are based on $(771.6\pm 10.6)\times {10}^6$ $B\overline{B}$ events collected at the $\mathrm{\Upsilon }(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. The fractions of longitudinal polarization of the $D^{**}$ states as well as partial wave fractions of the $D_1(2430{)}^0$ are obtained. We also set a 90% confidence level upper limit for the product of branching fractions of $\mathcal{B}({\overline{B}}^0\to D^{*+}{b}_1(1235{)}^{-})\times \mathcal{B}(b_1(1235{)}^{-}\to \omega {\pi }^{-})$. The measurements show evidence of nontrivial final-state interaction phases for the $\rho$-meson-like amplitudes.

We study the finite temperature behavior of the $CPT$-even pure-photon sector of the standard model extension, which is defined by the standard Maxwell Lagrangian plus the term $(k_F{)}_{\mu \nu \alpha \beta }{F}^{\mu \nu }{F}^{\alpha \beta }$. The Hamiltonian analysis is performed, from which the degrees of freedom and constraints of the theory are derived. We have explicitly calculated the partition function for an arbitrary configuration of the $(k_F{)}_{\mu \nu \alpha \beta }$ coefficients, to second order, and we have used it to obtain the thermodynamic properties of the modified photon sector. We find the correction to the frequency dependence in Planck’s radiation law, and we identify that the total energy density is adjusted, relative to the standard scenario, by a global proportionality constant containing the Lorentz-violating contributions. Nevertheless, the equation of state is not affected by these modifications.

We investigate the scalar and the tensor perturbations of the ${\phi }^2$ inflation model in the strong-gravity limit of Eddington-inspired Born-Infeld (EiBI) theory. In order to consider the strong EiBI-gravity effect, we take the value of $\kappa$ large, where $\kappa$ is the EiBI theory parameter. The energy density of the Universe at the early stage is very high, and the Universe is in a strong-gravity regime. Therefore, the perturbation feature is not altered from what was investigated earlier. At the attractor inflationary stage, however, the feature is changed in the strong EiBI-gravity limit. The correction to the scalar perturbation in this limit comes mainly via the background matter field, while that to the tensor perturbation comes directly from the gravity ($\kappa$) effect. The change in the value of the scalar spectrum is little compared with that in the weak EiBI-gravity limit, or in general relativity. The form of the tensor spectrum is the same as that in the weak limit, but the value of the spectrum can be suppressed down to zero in the strong limit. Therefore, the resulting tensor-to-scalar ratio can also be suppressed in the same way, which makes the ${\phi }^2$ model in EiBI theory viable.

Superheavy dark matter may show its presence in high-energy neutrino signals detected on Earth. From the latest results of IceCube, we could set the strongest lower bound on the lifetime of dark matter beyond 100 TeV around ${10}^{28}s$. The excess around a PeV is noticed and may be interpreted as the first signal of dark matter even though further confirmation and dedicated searches are invited.

The combination of $S$-matrix unitarity and the dynamics of thermal freeze-out for massive relic particles (denoted here simply by WIMPs) implies a lower limit on the density of such particles, that provide a (potentially subdominant) contribution to dark matter. This then translates to lower limits to the signal rates for a variety of techniques for direct and indirect detection of dark matter. For illustration, we focus on models where annihilation is $s$-wave dominated. We derive lower limits to the flux of gamma rays from WIMP annihilation at the Galactic center; direct detection of WIMPs; energetic neutrinos from WIMP annihilation in the Sun; and the effects of WIMPs on the angular power spectrum and frequency spectrum of the cosmic microwave background radiation. The results suggest that a variety of dark-matter-search techniques may provide interesting avenues to seek new physics, even if WIMPs do not constitute all the dark matter. While the limits are quantitatively some distance from the reach of current measurements, they may be interesting for long-range planning exercises.

We study the power spectrum of super-Hubble fluctuations of an inflatonlike scalar field, the “system,” coupled to another scalar field, the “environment” during de Sitter inflation. We obtain the reduced density matrix for the inflaton fluctuations by integrating out the environmental degrees of freedom. These are considered to be massless and conformally coupled to gravity as a proxy to describe degrees of freedom that remain sub-Hubble all throughout inflation. The time evolution of the density matrix is described by a quantum master equation, which describes the decay of the vacuum state, the production of particles and correlated pairs and quantum entanglement between super and sub-Hubble degrees of freedom. The quantum master equation provides a nonperturbative resummation of secular terms from self-energy (loop) corrections to the inflaton fluctuations. In the case studied here these are Sudakov-type double logarithms which result in the decay of the power spectrum of inflaton fluctuations upon horizon crossing with a concomitant violation of scale invariance. The reduced density matrix and its quantum master equation furnish a powerful nonperturbative framework to study the effective field theory of long wavelength fluctuations by tracing short wavelength degrees of freedom.

Motivated by the coincidence between the Hubble scale during inflation and the typical seesaw neutrino mass scale, we present a supergravity model in which the inflaton is identified with a linear combination of right-handed sneutrino fields. The model accommodates an inflaton potential that is flatter than quadratic chaotic inflation, resulting in a tensor-to-scalar ratio that is measurable but not yet ruled out. Small $CP$ violation in the neutrino mass matrix and supersymmetry breaking yield an evolution in the complex plane for the sneutrino fields. This induces a net lepton charge that, via the Affleck–Dine mechanism, can be the origin of the observed baryon asymmetry of the Universe.

We compute one of the second order transport coefficients arising from the chiral anomaly in a high-temperature weakly coupled regime of quark-gluon plasma. This transport coefficient is responsible for the $CP$-odd current that is proportional to the time derivative of the magnetic field, and can be considered as a first correction to the chiral magnetic conductivity at finite, small frequency. We observe that this transport coefficient has a nonanalytic dependence on the coupling as $\sim 1/(g^4\log (1/g))$ at the weak coupling regime, which necessitates a resummation of infinite ladder diagrams with leading pinch singularities to get a correct leading log result, a feature quite similar to what one finds in the computation of electric conductivity. We formulate and solve the relevant $CP$-odd Schwinger-Dyson equation in real-time perturbation theory that reduces to a coupled set of second order differential equations at leading log order. Our result for this second order transport coefficient indicates that chiral magnetic current has some resistance to the time change of the magnetic field; this shall be called the “chiral induction effect.” We also discuss the case of color current induced by a color magnetic field.

Quantum chromodynamics is notoriously difficult to solve at nonzero baryon density, and most models or effective theories of dense quark or nuclear matter are restricted to a particular density regime and/or a particular form of matter. Here we study dense (and mostly cold) matter within the holographic Sakai-Sugimoto model, aiming at a strong-coupling framework in the wide density range between nuclear saturation density and ultrahigh quark matter densities. The model contains only three parameters, and we ask whether it fulfills two basic requirements of real-world cold and dense matter, a first-order onset of nuclear matter and a chiral phase transition at high density to quark matter. Such a model would be extremely useful for astrophysical applications because it would provide a single equation of state for all densities relevant in a compact star. Our calculations are based on two approximations for baryonic matter—first, an instanton gas and, second, a homogeneous ansatz for the non-Abelian gauge fields on the flavor branes of the model. While the instanton gas shows chiral restoration at high densities but an unrealistic second-order baryon onset, the homogeneous ansatz behaves exactly the other way around. Our study, thus, provides all ingredients that are necessary for a more realistic model and allows for systematic improvements of the applied approximations.

Different formulations of Einstein’s equations used in numerical relativity can affect not only the stability but also the accuracy of numerical simulations. In the original Baumgarte-Shapiro-Shibata-Nakamura (BSSN) formulation, the loss of the angular momentum, $J$, is non-negligible in highly spinning single black hole evolutions. This loss also appears, usually right after the merger, in highly spinning binary black hole simulations, The loss of $J$ may be attributed to some unclear numerical dissipation. Reducing unphysical dissipation is expected to result in more stable and accurate evolutions. In the previous work [H.-J. Yo et al., Phys. Rev. D 86, 064027 (2012).] we proposed several modifications which are able to prevent black hole evolutions from the unphysical dissipation, and the resulting simulations are more stable than in the traditional BSSN formulation. Specifically, these three modifications (M1, M2, and M3) enhance the effects of stability, hyperbolicity, and dissipation of the formulation. We experiment further in this work with these modifications, and demonstrate that these modifications improve the accuracy and also effectively suppress the loss of $J$, particularly in the black hole simulations with an initially large ratio of $J$ and a square of the ADM mass.

The European Space Agency (ESA) selected the gravitational universe as the science theme for L3, a large space mission with a planned launch in 2034. NASA expressed a strong interest in joining ESA as a junior partner. The goal of the mission is the detection of gravitational waves of frequencies between 0.1 mHz and 0.1 Hz, where many long-lived sources are expected to be steady emitters of gravitational waves. Most likely, the mission design will evolve out of the earlier Laser Interferometer Space Antenna (LISA) concept. The interferometric heterodyne phase readout in LISA is performed by phase meters developed specifically to handle the low light powers and Doppler-drift of laser frequencies that appear as complications in the mission baseline. LISA requires the frequency noise of its seed lasers to be below $300\mathrm{Hz}/\sqrt{\mathrm{Hz}}$ throughout the measurement band due to uncertainties in the absolute interferometer arm lengths. We have developed and successfully demonstrated Heterodyne Stabilization (HS), a novel cavity-laser frequency stabilization method that integrates well into the LISA mission baseline due to similar component demand. The cavities for the test setup were assembled with Clearceram-Z spacers, an ultralow thermal expansion coefficient material with potential applicability in interferometric space missions. Using HS, we were able to suppress the frequency noise of two lasers in a bench-top experiment to a level that meets the LISA requirement, suggesting both HS and Clearceram-Z can be considered in future mission concepts.

We investigate methods to explore the $CP$ nature of the $t\overline{t}h$ coupling at the LHC, focusing on associated production of the Higgs boson with a $t\overline{t}$ pair. We first discuss the constraints implied by low-energy observables and by the Higgs-rate information from available LHC data, emphasizing that they cannot provide conclusive evidence on the nature of this coupling. We then investigate kinematic observables that could probe the $t\overline{t}h$ coupling directly, in particular, quantities that can be constructed out of just laboratory-frame kinematics. We define one such observable by exploiting the fact that $t\overline{t}$ spin correlations do also carry information about the $CP$ nature of the $t\overline{t}h$ coupling. Finally, we introduce a $CP$-odd quantity and a related asymmetry, able to probe $CP$ violation in the $t\overline{t}h$ coupling and likewise, constructed out of laboratory-frame momenta only.

We continue our investigation of $2+1$ flavor QCD thermodynamics using dynamical Wilson fermions in the fixed scale approach. Two additional pion masses, approximately 440 MeV and 285 MeV, are added to our previous work at 545 MeV. The simulations were performed at 3 or 4 lattice spacings at each pion mass. The renormalized chiral condensate, strange quark number susceptibility and Polyakov loop is obtained as a function of the temperature and we observe a decrease in the light chiral pseudocritical temperature as the pion mass is lowered while the pseudocritical temperature associated with the strange quark number susceptibility or the Polyakov loop is only mildly sensitive to the pion mass. These findings are in agreement with previous continuum results obtained in the staggered formulation.