A simultaneous investigation of the space- and timelike electromagnetic form factors of the charged kaon is presented within the framework of light-cone QCD, with perturbative $k_T$ factorization including Sudakov suppression. The effects of power suppressed subleading twists and the genuine soft QCD corrections turn out to be dominant at low- and moderate-energies/momentum transfers. Our predictions agree well with the available moderate-energy experimental data, including the recent results from the CLEO measurements and certain estimates based on the phenomenological analyses of $J/\psi$ decays.

We report the observation of electroweak single top quark production in $3.2{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collision data collected by the Collider Detector at Fermilab at $\sqrt{s}=1.96\mathrm{TeV}$. Candidate events in the $W+\mathrm{\text{jets}}$ topology with a leptonically decaying $W$ boson are classified as signal-like by four parallel analyses based on likelihood functions, matrix elements, neural networks, and boosted decision trees. These results are combined using a super discriminant analysis based on genetically evolved neural networks in order to improve the sensitivity. This combined result is further combined with that of a search for a single top quark signal in an orthogonal sample of events with missing transverse energy plus jets and no charged lepton. We observe a signal consistent with the standard model prediction but inconsistent with the background-only model by 5.0 standard deviations, with a median expected sensitivity in excess of 5.9 standard deviations. We measure a production cross section of ${2.3}_{-0.5}^{+0.6}(\mathrm{stat}+\mathrm{sys})\mathrm{pb}$, extract the value of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{tb}|={0.91}_{-0.11}^{+0.11}(\mathrm{stat}+\mathrm{sys})\pm 0.07(\mathrm{\text{theory}})$, and set a lower limit $|V_{tb}|>0.71$ at the 95% C.L., assuming $m_t=175\mathrm{GeV}/c^2$.

We consider the evolution of primordial black holes by including nonstationarity in the formation process and accretion of radiation in Brans-Dicke theory. Specifically, we focus on how $\eta$, the fraction of the horizon mass the black hole comprises capturing nonstationarity, affects the lifetimes of these primordial black holes. Our calculation reveals that the primordial black hole dynamics is controlled by the product $f\eta$ where $f$ is the accretion efficiency. We also estimate the impact of $\eta$ through $f\eta$ on the primordial black holes’ initial mass fraction constraint obtained from the $\gamma$-ray background limit.

Using Lorentz-covariant spinor helicity formalism, we reorganize the unitary scalar superfield light-cone path integral for the $\mathcal{N}=4$ supersymmetric Yang-Mills theory. In new variables in the chiral Fourier superspace, the quadratic and cubic parts of the classical action have manifest Lorentz, kinematical and dynamical supersymmetry, with the exception of terms which contribute only to the contact terms in the supergraphs with propagators shrinking to a point. These terms have the same structure as supergraphs with quartic light-cone vertices, which break dynamical supersymmetry. We present evidence that all complicated terms breaking dynamical supersymmetry have to cancel and therefore can be omitted. It is plausible that the new form of the path integral leads to a set of relatively simple unitarity based rules with manifest $\mathcal{N}=4$ supersymmetry.

We improve and update the discussion, given some years ago by my collaborators and me, of infrared divergences and bremsstrahlung in one-loop gluon scattering probabilities in lightcone gauge. In that work, we showed that adding soft and collinear gluon radiation, satisfying simple Lorentz invariant constraints, not only canceled all IR divergences, but resulted in compact expressions for the consequent scattering probabilities. Here we impose less restrictive (albeit noncovariant) constraints on the unobserved radiation, which increases the high energy ($s$) fixed momentum transfer ($t$) behavior of the total probabilities from $-{ln}^{2}s$ to $\ln s\ln t$, a behavior shared by the (IR divergent) elastic probabilities. Using this new treatment we also make a much more detailed comparison of the lightcone results to covariant calculations using dimensional regularization, finding complete agreement between the two styles of calculation.

High precision spectroscopy can provide a sensitive tool to test Coulomb’s law on atomic length scales. This can then be used to constrain particles such as extra “hidden” photons or minicharged particles that are predicted in many extensions of the standard model, and which cause small deviations from Coulomb’s law. In this paper we use a variety of transitions in atomic hydrogen, hydrogenic ions, and exotic atoms to probe Coulomb’s law. This extends the region of pure Coulomb’s law tests to larger masses. For hidden photons and minicharged particles this region is already tested by other astrophysical and laboratory probes. However, future tests of true muonium and muonic atoms are likely to probe new parameter space and therefore have good discovery potential for new physics. Finally, we investigate whether the discrepancy between the theoretical calculation of the $2s_{1/2}^{F=1}-2p_{3/2}^{F=2}$ transition in muonic hydrogen and its recent experimental measurement at PSI can be explained by the existence of a hidden photon. This explanation is ruled out by measurements of the Lamb shift in ordinary hydrogen.

Two-field slow-roll inflation is the most conservative modification of a single-field model. The main motivations to study it are its entropic mode and non-Gaussianity. Several years ago, for a two-field model with additive separable potentials, Vernizzi and Wands invented an analytic method to estimate its non-Gaussianities. Later on, Choi et al. applied this method to the model with multiplicative separable potentials. In this note, we design a larger class of models whose non-Gaussianity can be estimated by the same method. Under some simplistic assumptions, roughly these models are unlikely able to generate a large non-Gaussianity. We look over some specific models of this class by scanning the full parameter space, but still no large non-Gaussianity appears in the slow-roll region. These models and scanning techniques would be useful for a future model hunt if observational evidence shows up for two-field inflation.

We analyzed the electron neutrino data of the Gallium radioactive source experiments and the electron antineutrino data of the reactor Bugey and Chooz experiments in terms of neutrino oscillations allowing for a $CPT$-violating difference of the squared masses and mixings of neutrinos and antineutrinos. We found that the discrepancy between the disappearance of electron neutrinos indicated by the data of the Gallium radioactive source experiments and the limits on the disappearance of electron antineutrinos given by the data of reactor experiments reveal a positive $CPT$-violating asymmetry of the effective neutrino and antineutrino mixing angles (with a statistical significance of about $3.5\sigma$), whereas the squared-mass asymmetry is practically not bounded.

We investigate the nontrivial interplay between geometry and temperature in the Casimir effect for the sphere-plate and cylinder-plate configurations. At low temperature, the thermal contribution to the Casimir force is dominated by this interplay, implying that standard approximation techniques such as the proximity force approximation (PFA) are inapplicable even in the limit of small surface separation. Thermal fluctuations on scales of the thermal wavelength lead to a delocalization of the thermal force density at low temperatures. As a consequence, the temperature dependence strongly differs from naive expectations. Most prominently, thermal forces can develop nonmonotonic behavior below a critical temperature. We perform a comprehensive study of such geothermal phenomena in these Casimir geometries, using analytical and numerical worldline techniques for Dirichlet scalar fluctuations.

The linear sigma model with quarks at very low temperatures provides an effective framework for the thermodynamics of the strong interaction in cold and dense matter. It is especially useful in the description of the chiral transition at densities that are still not probed in accelerators but expected to be found in compact stars and protoneutron star matter. Using the $\overline{\mathrm{MS}}$ one-loop effective potential, we compute quantities that are relevant in the process of nucleation of droplets of quark matter in this scenario. In particular, we show that the model predicts a surface tension of $\Sigma \sim 5–15\mathrm{MeV}/{\mathrm{fm}}^2$. Including temperature effects and vacuum logarithmic corrections, we find a clear competition between these features in characterizing the dynamics of the chiral phase conversion, so that if the temperature is low enough the consistent inclusion of vacuum corrections could help preventing the nucleation of quark matter at high densities. We also discuss the first interaction corrections that come about at two-loop order. Low values of the surface tension, as the ones we find in this simplified chiral description, could render nucleation of quark matter possible during the early postbounce stage of core-collapse supernovae.

We calculate the weak interaction rates of selected light nuclei during the epoch of big bang nucleosynthesis (BBN), and we assess the impact of these rates on nuclear abundance flow histories and on final light element abundance yields. We consider electron and electron antineutrino captures on ${}^3\mathrm{He}$ and ${}^7\mathrm{Be}$, and the reverse processes of positron capture and electron neutrino capture on ${}^3\mathrm{H}$ and ${}^7\mathrm{Li}$. We also compute the rates of positron and electron neutrino capture on ${}^6\mathrm{He}$. We calculate beta and positron decay transitions where appropriate. As expected, the final standard BBN abundance yields are little affected by addition of these weak processes, though there can be slight alterations of nuclear flow histories. However, nonstandard BBN scenarios, e.g., those involving out of equilibrium particle decay with energetic final state neutrinos, may be affected by these processes.

The violation of the third law of thermodynamics for metals described by the Drude model and for dielectrics with finite dc conductivity is one of the most interesting problems in the field of the Casimir effect. It manifests itself as a nonvanishing of the entropy for vanishing temperature. We review the relevant calculations for plane surfaces and calculate the corresponding contributions for a ball in front of a plane. In this geometry, these appear in much the same way as for parallel planes. We conclude that the violation of the 3rd law is not related to the infinite size of the planes.

The calculation of entanglement entropy $S$ of quantum fields in spacetimes with horizon shows that, quite generically, $S$ is (a) proportional to the area $A$ of the horizon and (b) divergent. I argue that this divergence, which arises even in the case of Rindler horizon in flat spacetime, is yet another indication of a deep connection between horizon thermodynamics and gravitational dynamics. In an emergent perspective of gravity, which accommodates this connection, the fluctuations around the equipartition value in the area elements will lead to a minimal quantum of area $\mathcal{O}(1)L_P^2$, which will act as a regulator for this divergence. In a particular prescription for incorporating the $L_P^2$ as zero-point-area of spacetime, this does happen and the divergence in entanglement entropy is regularized, leading to $S\propto A/L_P^2$ in Einstein gravity. In more general models of gravity, the surface density of microscopic degrees of freedom is different which leads to a modified regularization procedure and the possibility that the entanglement entropy—when appropriately regularized—matches the Wald entropy.

We calculate the pair-annihilation cross section of real scalar singlet dark matter into two monoenergetic photons. We derive constraints on the theory parameter space from the Fermi limits on gamma-ray lines, and we compare with current limits from direct dark matter detection. We show that the new limits, albeit typically relevant only when the dark matter mass is close to half the standard model Higgs mass, rule out regions of the theory parameter space that are otherwise not constrained by other observations or experiments. In particular, the new excluded regions partly overlap with the parameter space where real scalar singlet dark matter might explain the anomalous signals observed by CDMS. We also calculate the lifetime of unstable vacuum configurations in the scalar potential, and show that the gamma-ray limits are quite relevant in regions where the electroweak vacuum is metastable with a lifetime longer than the age of the Universe.

Multidimensional core-collapse supernova simulations exhibit turbulence of large amplitude and over large scales. As neutrinos pass through the supernova mantle the turbulence is expected to modify their evolution compared to the case where the explosion is free of turbulence. In this paper we study this turbulence effect upon the neutrinos modeling the turbulence expected from multidimensional simulations by adding matter density fluctuations to density profiles taken from one-dimensional hydrodynamical simulations. We investigate the impact upon the supernova neutrino transition probabilities as a function of the neutrino mixing angle ${\theta }_{13}$ and turbulence amplitude. In the high resonant channel and with large ${\theta }_{13}$ values we find that turbulence is effectively two flavor for fluctuation amplitudes $\lesssim 1\%$ and have identified a new effect due to the combination of turbulence and multiple high resonances that leads to a sensitivity to fluctuations amplitudes as small as $\sim 0.001\%$. At small values of ${\theta }_{13}$, beyond the range achievable in Earth based experiments, we find that turbulence leads to new flavor transient effects in the channel where the Mikheev-Smirnov-Wolfenstein high resonance occurs. Finally, we investigate large amplitude fluctuations which lead to three-flavor effects due to broken high-low factorization and significant nonresonant transitions and identify two nonresonant turbulence effects, one depending on the ${\theta }_{13}$, and the other independent of this angle and due to the low Mikheev-Smirnov-Wolfenstein resonance.

Recently, the CoGeNT collaboration reported weakly interacting massive particle candidate-signal events exceeding the known backgrounds where the light WIMP with large cross section is supported. Motivated by this issue, we analyze a light neutralino dark matter scenario with a very light $CP$-even Higgs mediation in the elastic scattering process, which provides the mass and direct detection cross section to explain the CoGeNT result. To be compatible with the result of LEP experiments, the light $CP$-even Higgs is favored to be at around 9–10 GeV. Such a scenario can be realized in the “beyond the minimal supersymmetric standard model” context. The relic abundance consistent with the WMAP result can be obtained when twice neutralino mass is close to the light Higgs mass via the resonance enhancement of the annihilation cross section. As a result, the neutralino mass is predicted to be at around 5–6 GeV.

An unbroken discrete symmetry, analogous to $G$ parity in QCD, exists in standard model extensions with vectorlike coupling of electroweak $SU(2)$ to “hidden sector” fermions that are confined by a strong gauge force. For an arbitrary irreducible $SU(2)$ representation of the hidden sector fermions, the lightest hidden sector states form an isotriplet of “pions” with calculable mass splittings and couplings to standard model fields. The parity can be extended to fermions in real representations of color $SU(3)$, and can provide dark matter candidates with distinct collider signatures.

We give field theory descriptions of the time-reversal invariant quantum spin Hall insulator in $2+1$ dimensions and the particle-hole symmetric insulator in $1+1$ dimensions in terms of massive Dirac fermions. Integrating out the massive fermions we obtain a low-energy description in terms of a topological field theory, which is entirely determined by anomaly considerations. This description allows us to easily construct low-energy effective actions for the corresponding fractional topological insulators, potentially corresponding to new states of matter. We give a holographic realization of these fractional states in terms of a probe brane system, verifying that the expected topologically protected transport properties are robust even at strong coupling.