Using $q$-theory, we show that the electroweak crossover can generate a remnant vacuum energy density $\Lambda \sim E_{\mathrm{ew}}^8/E_{\mathrm{Planck}}^4$, with effective electroweak energy scale $E_{\mathrm{ew}}\sim {10}^3\mathrm{GeV}$ and reduced Planck-energy scale $E_{\mathrm{Planck}}\sim {10}^{18}\mathrm{GeV}$. The obtained expression for the effective cosmological constant $\Lambda$ may be a crucial input for the suggested solution by Arkani-Hamed et al. of the triple cosmic coincidence puzzle (why the orders of magnitude of the energy densities of vacuum, matter, and radiation are approximately the same in the present Universe).

We present the results of an exploratory lattice QCD calculation of three-baryon systems through a high statistics study of one ensemble of anisotropic clover gauge-field configurations with a pion mass of $m_{\pi }\sim 390\mathrm{MeV}$. Because of the computational cost of the necessary contractions, we focus on correlation functions generated by interpolating operators with the quantum numbers of the ${\Xi }^0{\Xi }^{0}n$ system, one of the least demanding three-baryon systems in terms of the number of contractions. We find that the ground state of this system has an energy of $E_{{\Xi }^0{\Xi }^{0}n}=3877.9\pm 6.9\pm 9.2\pm 3.3\mathrm{MeV}$ corresponding to an energy shift due to interactions of $\delta E_{{\Xi }^0{\Xi }^{0}n}=E_{{\Xi }^0{\Xi }^{0}n}-2M_{{\Xi }^0}-M_n=4.6\pm 5.0\pm 7.9\pm 4.2\mathrm{MeV}$. There are a significant number of time slices in the three-baryon correlation function for which the signal-to-noise ratio is only slowly degrading with time. This is in contrast to the exponential degradation of the signal-to-noise ratio that is observed at larger times, and is due to the suppressed overlap of the source and sink interpolating operators that are associated with the variance of the three-baryon correlation function onto the lightest eigenstates in the lattice volume (mesonic systems). As one of the motivations for this area of exploration is the calculation of the structure and reactions of light nuclei, we also present initial results for a system with the quantum numbers of the triton ($pnn$). This present work establishes a path to multibaryon systems, and shows that lattice QCD calculations of the properties and interactions of systems containing four and five baryons are now within sight.

Using the CLEO-c detector at the Cornell Electron Storage Ring, we have measured inclusive and exclusive cross sections for the production of $D^{+}$, $D^0$ and $D_s^{+}$ mesons in $e^{+}{e}^{-}$ annihilations at 13 center-of-mass energies between 3.97 and 4.26 GeV. Exclusive cross sections are presented for final states consisting of two charm mesons ($D\overline{D}$, $D^{*}\overline{D}$, $D^{*}{\overline{D}}^{*}$, $D_s^{+}{D}_s^{-}$, $D_s^{*+}{D}_s^{-}$, and $D_s^{*+}{D}_s^{*-}$) and for processes in which the charm-meson pair is accompanied by a pion. No enhancement in any final state is observed at the energy of the $Y(4260)$.

Using hard-loop (HL) effective theory for an anisotropic non-Abelian plasma, which even in the static limit involves nonvanishing HL vertices, we calculate the imaginary part of the static next-to-leading-order gluon self-energy in the limit of a small anisotropy and with external momentum parallel to the anisotropy direction. At leading order, the static propagator has spacelike poles corresponding to plasma instabilities. On the basis of a calculation using bare vertices, it has been conjectured that, at next-to-leading order, the static gluon self-energy acquires an imaginary part which regulates these spacelike poles. We find that the one-loop resummed expression taken over naively from the imaginary-time formalism does yield a nonvanishing imaginary part even after including all HL vertices. However, this result is not correct. Starting from the real-time formalism, which is required in a nonequilibrium situation, we construct a resummed retarded HL propagator with correct causality properties and show that the static limit of the retarded one-loop-resummed gluon self-energy is real. This result is also required for the time-ordered propagator to exist at next-to-leading order.

Quantum fluctuations in the density of a fluid with a linear phonon dispersion relation are studied. In particular, we treat the changes in these fluctuations due to nonclassical states of phonons and to the presence of boundaries. These effects are analogous to similar effects in relativistic quantum field theory, and we argue that the case of the fluid is a useful analog model for effects in field theory. We further argue that the changes in the mean squared density are, in principle, observable by light scattering experiments.

We provide further evidence for the nontrivial interplay between geometry and temperature in the Casimir effect. We investigate the temperature dependence of the Casimir force between an inclined semi-infinite plate above an infinite plate in $D$ dimensions using the worldline formalism. Whereas the high-temperature behavior is always found to be linear in $T$ in accordance with dimensional-reduction arguments, different power-law behaviors at small temperatures emerge. Unlike the case of infinite parallel plates, which shows the well-known $T^D$ behavior of the force, we find a $T^{D-1}$ behavior for inclined plates, and a $\sim T^{D-0.3}$ behavior for the edge effect in the limit where the plates become parallel. The strongest temperature dependence $\sim T^{D-2}$ occurs for the Casimir torque of inclined plates. Numerical as well as analytical worldline results are presented.

We discuss the quantum and classical dynamics of a particle with spin in the gravitational field of a rotating source. A relativistic equation describing the motion of classical spin in curved spacetimes is obtained. We demonstrate that the precession of the classical spin is in a perfect agreement with the motion of the quantum spin derived from the Foldy-Wouthuysen approach for the Dirac particle in a curved spacetime. We show that the precession effect depends crucially on the choice of a tetrad. The results obtained are compared to the earlier computations for different tetrad gauges.

The properties of the gravitational energy-momentum 3-form and of the superpotential 2-form are discussed in the covariant teleparallel framework, where the Weitzenböck connection represents inertial effects related to the choice of the frame. Because of its odd asymptotic behavior, the contribution of the inertial effects often yields unphysical (divergent or trivial) results for the total energy of the system. However, in the covariant teleparallel approach, the energy is always finite and nontrivial. The teleparallel connection plays a role of a regularizing tool which subtracts the inertial effects without distorting the true gravitational contribution. As a crucial test of the covariant formalism, we reanalyze the computation of the total energy of the Schwarzschild and the Kerr solutions.

Unparticle degrees of freedom, no matter how weakly coupled to the standard model particles, must affect the evolution of a black hole, which thermally decays into all available degrees of freedom. We develop a method for calculating the grey-body factors for scalar unparticles for $3+1$ and higher dimensional black holes. We find that the power emitted in unparticles may be quite different from the power emitted in ordinary particles. Depending on the parameters in the model, unparticles may become the dominant channel. This is of special interest for small primordial black holes and also in models with low scale quantum gravity where the experimental signature may significantly be affected. We also discuss the sensitivity of the results on the (currently unknown) unparticle normalization.

We investigate the impact of a nonstandard time evolution of the dark matter component on current cosmological bounds from cosmic microwave background (CMB) anisotropies. We found that a less than 0.1% variation in the effective dark matter equation of state $w_{\mathrm{dm}}$ can drastically change current CMB bounds on the matter density, the Hubble parameter and the age of the Universe. A flat universe without dark energy could provide an excellent fit to current CMB data, providing that $w_{\mathrm{dm}}\sim -{10}^{-2}$.

Braginsky, Gorodetsky, and Vyatchanin have shown that thermorefractive fluctuations are an important source of noise in interferometric gravitational-wave detectors. In particular, the thermorefractive noise in the GEO600 beamsplitter is expected to make a substantial contribution to the interferometer’s total noise budget. Here, we present a new computation of the GEO600 thermorefractive noise, which takes into account the beam’s elliptical profile and, more importantly, the fact that the laser beam induces a standing electromagnetic wave in the beamsplitter. The use of updated parameters results in the overall reduction of the calculated noise amplitude by a factor of $\sim 5$ in the low-frequency part of the GEO600 band, compared to the previous estimates. We also find, by contrast with previous calculations, that thermorefractive fluctuations result in white noise between 600 Hz and 39 MHz, at a level of $8.5·{10}^{-24}{\mathrm{Hz}}^{-1/2}$. Finally, we describe a new type of thermal noise, which we call the thermochemical noise. This is caused by a random motion of optically active chemical impurities or structural defects in the direction along a steep intensity gradient of the standing wave. We discuss the potential relevance of the thermochemical noise for GEO600.

We compute the entropy density of the confined phase of QCD without quarks on the lattice to very high accuracy. The results are compared to the entropy density of free glueballs, where we include all the known glueball states below the two-particle threshold. We find that an excellent, parameter-free description of the entropy density between $0.7T_c$ and $T_c$ is obtained by extending the spectrum with the exponential spectrum of the closed bosonic string.

We present a search for charged Higgs bosons in decays of top quarks, in the mass range $80<m_{H^{\pm }}<155\mathrm{GeV}$, assuming the subsequent decay $H^{+}\to {\tau }^{+}{\nu }_{\tau }$ (and its charge conjugate). Using $0.9{\mathrm{fb}}^{-1}$ of $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ data collected with the D0 detector at the Fermilab Tevatron $p\overline{p}$ collider, operating at a center of mass energy $\sqrt{s}=1.96\mathrm{TeV}$, we find no evidence for a $H^{\pm }$ signal. Hence we exclude branching ratios $B(t\to H^{+}b)>0.24$ for $m_{H^{\pm }}=80\mathrm{GeV}$ and $B(t\to H^{+}b)>0.19$ for $m_{H^{\pm }}=155\mathrm{GeV}$ at the 95% C.L.

Current constraints on the dark energy equation of state parameter, $w$, are expected to be improved by more than 1 order of magnitude in the next decade. If $|w-1|\gtrsim 0.01$ around the present time, but the dark energy dynamics is sufficiently slow, it is possible that future constraints will rule out a cosmological constant while being consistent with a time-independent equation of state parameter. In this paper, we show that although models with such behavior can be constructed, they do require significant fine-tuning. Therefore, if the observed acceleration of the Universe is induced by a dark energy component, then finding $w\ne -1$ would, on its own, constitute very strong evidence for a dynamical dark energy equation of state.

We extend the Kazama-Suzuki construction of models with $\mathcal{N}=(2,2)$ world-sheet supersymmetry to cosets $S/K$ of supergroups. Among the admissible target spaces that allow for an extension to $\mathcal{N}=2$ superconformal algebras are some simple Lie supergroups, including $\mathrm{PSL}(\mathrm{N}|\mathrm{N})$. Our general analysis is illustrated at the example of the $\mathcal{N}=1$ Wess-Zumino-Novikov-Witten model on $\mathrm{GL}(1|1)$. After constructing its $\mathcal{N}=2$ superconformal algebra we determine the (anti-)chiral ring of the theory. It exhibits an interesting interplay between world-sheet and target space supersymmetry.

Threshold effects related to fermion masses are considered for an all-order $\beta$-function based on a background field momentum subtraction scheme. Far away from all thresholds, the suggested $\beta$-function reduces to the conjectured all-order form inspired by the Novikov–Shifman–Vainshtein–Zakharov $\beta$-function of $\mathcal{N}=1$ supersymmetric gauge theories with a fixed integer number of fermion flavors. At (formally) infinite masses the corresponding pure Yang–Mills $\beta$-function is recovered. We discuss applications to the phase diagram of non-Abelian field theories.

In this paper we have recalled the semiclassical metric obtained from a classical analysis of the loop quantum black hole (LQBH). We show that the regular Reissner–Nordström-like metric is self-dual in the sense of $T$-duality: the form of the metric obtained in loop quantum gravity is invariant under the exchange $r\to a_0/r$ where $a_0$ is proportional to the minimum area in loop quantum gravity and $r$ is the standard Schwarzschild radial coordinate at asymptotic infinity. Of particular interest, the symmetry imposes that if an observer in $r\to +\infty$ sees a black hole of mass $m$ an observer in the other asymptotic infinity beyond the horizon (at $r\approx 0$) sees a dual mass $m_P/m$. We then show that small LQBH are stable and could be a component of dark matter. Ultralight LQBHs created shortly after the big bang would now have a mass of approximately ${10}^{-5}{m}_P$ and emit radiation with a typical energy of about ${10}^{13}–{10}^{14}\mathrm{eV}$ but they would also emit cosmic rays of much higher energies, albeit few of them. If these small LQBHs form a majority of the dark matter of the Milky Way’s Halo, the production rate of ultra-high-energy-cosmic-rays (UHECR) by these ultralight black holes would be compatible with the observed rate of the Auger detector.

The quantization of Einstein-Maxwell theory with a cosmological constant is considered. We obtain all logarithmically divergent terms in the one-loop effective action that involve only the background electromagnetic field. This includes Lee-Wick–type terms, as well as those responsible for the renormalization group behavior of the electric charge (or fine structure constant). Of particular interest is the possible gauge condition dependence of the results, and we study this in some detail. We show that the traditional background-field method, that is equivalent to a more traditional Feynman diagram calculation, does result in gauge condition dependent results in general. One resolution of this is to use the Vilkovisky-DeWitt effective action method, and this is presented here. Quantum gravity is shown to lead to a contribution to the running charge not present when the cosmological constant vanishes. This reopens the possibility, suggested by Robinson and Wilczek, of altering the scaling behavior of gauge theories at high energies although our result differs. We show the possibility of an ultraviolet fixed point that is linked directly to the cosmological constant.

In loop quantum cosmology there may be a superinflation phase in the very early universe, in which a single scalar field with a negative power-law potential $V=-M^4(\varphi /M{)}^{\beta }$ plays an important role. Since the effective horizon $\sqrt{SD}/H$ controls the behavior of quantum fluctuation instead of the usual Hubble horizon, we assume the following inflation scenario: the superinflation starts when the quantum state of the scalar field emerges into the classical regime and ends when the effective horizon becomes the Hubble horizon, and the effective horizon scale never gets shorter than the Planck length. From consistency with the WMAP 5 yr data, we place a constraint on the parameters of the potential ($\beta$ and $M$) and the energy density at the end of the superinflation, depending on the volume correction parameter $n$.

Motivated by recent interest in redshifted 21 cm emission of intergalactic hydrogen, we investigate the 8.7 GHz ${}^2\mathrm{S}_{1/2}$ $F=0-1$ hyperfine transition of ${}^3\mathrm{He}^{+}$. While the primordial abundance of ${}^3\mathrm{He}$ relative to hydrogen is ${10}^{-5}$, the hyperfine spontaneous decay rate is 680 times larger. Furthermore, the antenna temperature is much lower at the frequencies relevant for the ${}^3\mathrm{He}^{+}$ transition compared to that of $z>6$ 21 cm emission. We find that the spin temperature of this 8.7 GHz line in the intergalactic medium is approximately the cosmic microwave background temperature, such that this transition is best observed in absorption against high-redshift, radio-bright quasars. We show that intergalactic 8.7 GHz absorption is a promising, unsaturated observable of the ionization history of intergalactic helium (for which $\mathrm{He}\mathrm{II}\to \mathrm{He}\mathrm{III}$ reionization is believed to complete at $z\sim 3$) and of the primordial ${}^3\mathrm{He}$ abundance. Instruments must reach $\sim 1\mu \mathrm{Jy}$ RMS noise in bands of 1 MHz on a 1 Jy source to directly resolve this absorption. However, in combination with H i $\mathrm{Ly}\alpha$ forest measurements, an instrument can statistically detect this absorption from $z>3$ with $30\mu \mathrm{Jy}$ RMS noise in 0.1 MHz spectral bands over 100 MHz, which may be within the reach of present instruments.