The conditions under which matrix orientifolding and supersymmetry transformations commute are known to be stringent. Here we present the cases possessing four or eight supercharges upon ${\mathbf{Z}}_3$ orbifolding followed by matrix orientifolding. These cases descend from the matrix models with eight plus eight supercharges. There are 50 in total, which we enumerate.

We investigate the problem of fine-tuning of the potential in the $\mathbb{K}\mathrm{L}\mathbb{M}\mathrm{T}$ warped flux compactification scenario for brane-antibrane inflation in Type IIB string theory. We argue for the importance of an additional parameter ${\psi }_0$ (approximated as zero by $\mathbb{K}\mathrm{L}\mathbb{M}\mathrm{T}$), namely, the position of the antibrane, relative to the equilibrium position of the brane in the absence of the antibrane. We show that for a range of values of a particular combination of the Kähler modulus, warp factor, and ${\psi }_0$, the inflaton potential can be sufficiently flat. We point out a novel mechanism for dynamically achieving flatness within this part of parameter space: the presence of multiple mobile branes can lead to a potential which initially has a metastable local minimum, but gradually becomes flat as some of the branes tunnel out. Eventually the local minimum disappears and the remaining branes slowly roll together, with assisted inflation further enhancing the effective flatness of the potential. With the addition of Kähler and superpotential corrections, this mechanism can completely remove the fine-tuning problem of brane inflation, within large regions of parameter space. The model can be falsified if future cosmic microwave background observations confirm the hint of a large running spectral index.

We consider theories with gravity, gauge fields and scalars in four-dimensional asymptotically flat space-time. By studying the equations of motion directly we show that the attractor mechanism can work for nonsupersymmetric extremal black holes. Two conditions are sufficient for this, they are conveniently stated in terms of an effective potential involving the scalars and the charges carried by the black hole. Our analysis applies to black holes in theories with $\mathcal{N}\le 1$ supersymmetry, as well as nonsupersymmetric black holes in theories with $\mathcal{N}=2$ supersymmetry. Similar results are also obtained for extremal black holes in asymptotically anti–de Sitter space and in higher dimensions.

In this paper we consider the cosmological implications of dark energy models with a coupled system of a dynamical scalar field (the quintessence) and the neutrinos. By detailed numerical calculations we study the various possibilities on the evolution and the fates of the Universe in this class of models. Our results show that due to the interaction with quintessence, neutrinos could be dominant over the quintessence in the future universe, however would eventually decay away.

We derive an effective theory describing the physics of a bulk brane in the context of the RS1 model. This theory goes beyond the usual low-energy effective theory in that it describes the regime where the bulk brane has a large velocity and the radion can change rapidly. We achieve this by concentrating on the region where the distance between the orbifold planes is small in comparison to the AdS length scale. Consequently our effective theory will describe the physics shortly before a bulk/boundary or boundary/boundary brane collision. We study the cosmological solutions and find that at large velocities, the bulk brane decouples from the matter on the boundary branes, a result which remains true for cosmological perturbations.

We show that the QCD axion can drive inflation via a series of tunneling events. For axion models with a softly broken $Z_N$ symmetry, the axion potential has a series of $N$ local minima and may be modeled by a tilted cosine. Chain inflation results along this tilted cosine: the field tunnels from an initial minimum near the top of the potential through a series of ever lower minima to the bottom. This results in sufficient inflation and reheating. QCD axions, potentially detectable in current searches, may thus simultaneously solve problems in particle physics and provide inflation.

We report on the first joint search for gravitational waves by the TAMA and LIGO collaborations. We looked for millisecond-duration unmodeled gravitational-wave bursts in 473 hr of coincident data collected during early 2003. No candidate signals were found. We set an upper limit of 0.12 events per day on the rate of detectable gravitational-wave bursts, at 90% confidence level. From software simulations, we estimate that our detector network was sensitive to bursts with root-sum-square strain amplitude above approximately $1–3\times {10}^{-19}{\mathrm{Hz}}^{-1/2}$ in the frequency band 700-2000 Hz. We describe the details of this collaborative search, with particular emphasis on its advantages and disadvantages compared to searches by LIGO and TAMA separately using the same data. Benefits include a lower background and longer observation time, at some cost in sensitivity and bandwidth. We also demonstrate techniques for performing coincidence searches with a heterogeneous network of detectors with different noise spectra and orientations. These techniques include using coordinated software signal injections to estimate the network sensitivity, and tuning the analysis to maximize the sensitivity and the livetime, subject to constraints on the background.

The joint ESA/NASA LISA mission consists of three spacecraft on heliocentric orbits, flying in a triangular formation of 5 Mkm each side, linked by infrared optical beams. The aim of the mission is to detect gravitational waves in a low frequency band. For properly processing the scientific data, the propagation delays between spacecraft must be accurately known. We thus analyze the propagation of light between spacecraft in order to systematically derive the relativistic effects due to the static curvature of the Schwarzschild space-time in which the spacecraft are orbiting with time-varying light distances. In particular, our analysis allows us to evaluate rigorously the Sagnac effect, and the gravitational (Einstein) redshift.

Since rotational or similar modulation of the solar neutrino flux would seem to be incompatible with the currently accepted theoretical interpretation of the solar neutrino deficit, it is important to determine whether or not such modulation occurs. There have been conflicting claims as to whether or not power-spectrum analysis of the Super-Kamiokande solar neutrino data yields indication of variability. Comparison of these claims is complicated by the fact that the relevant articles may use different data sets, different methods of analysis, and different procedures for significance estimation. The purpose of this article is to clarify the role of power-spectrum analysis. To this end, we analyze primarily the Super-Kamiokande 5-day data set, and we use a standard procedure for significance estimation as used by the Super-Kamiokande collaboration. We then analyze this data set, with this method of significance estimation, using six methods of power-spectrum analysis. Five of these have been used in published articles, and the other is a method that might have been used. We find that, with one exception, the results of these calculations are consistent with those of previously published analyses. We find that the power of the principal modulation (that at $9.43\mathrm{y}{\mathrm{r}}^{-1}$) is greater in analyses that take account of error estimates than in the basic Lomb-Scargle analysis that does not take account of error estimates. The corresponding significance level ranges between 98% and 99.3%, depending on the details of the analysis. Concerning the recent article by Koshio, we find that we can reproduce the results of his power-spectrum analysis but not the results of his Monte Carlo simulations, and we have a suggestion that may account for the difference. We also comment on a recent article by Yoo et al. We discuss, in terms of subdominant processes, possible neutrino-physics interpretations of the apparent variability of the Super-Kamiokande measurements, and we suggest steps that could be taken to resolve the question of variability of the solar neutrino flux.

Fermilab experiment E835 has studied reactions $\overline{p}p\to {\pi }^0{\pi }^0,{\pi }^0\eta ,\eta \eta ,$ ${\pi }^0{\eta }^{\prime }$ and $\eta {\eta }^{\prime }$ in the energy region of the ${\chi }_{c0}(1^3{P}_0)$ from $3340$ MeV to $3470$ MeV. Interference between resonant and continuum production is observed in the ${\pi }^0{\pi }^0$ and $\eta \eta$ channels, and the product of the input and output branching fractions is measured. Limits on resonant production are set for the ${\pi }^0\eta$ and ${\pi }^0{\eta }^{\prime }$ channels. An indication of interference is observed in the $\eta {\eta }^{\prime }$ channel. The technique for extracting resonance parameters in an environment dominated by continuum production is described.

Within five-dimensional compactified theories we discuss generalized periodicity and orbifold boundary conditions that allow for mixing between particles and antiparticles after a shift by the size of extra dimensions or after the orbifold reflection. A systematic strategy for constructing 4-dimensional models is presented, in particular, we find a general form of the periodicity and orbifold conditions that are allowed by consistency requirements. We formulate general conditions for a presence of massless Kaluza-Klein modes and discuss remaining gauge symmetry of the zero-mode sector. It is shown that if the orbifold twist operation transforms particles into antiparticles then the zero-mode fermions are 4-dimensional Majorana fermions. The possibility of explicit and spontaneous $CP$ violation is discussed. General considerations are illustrated by many Abelian and non-Abelian examples.

We provide a determination of the Gottfried sum from all available data, based on a neural network parametrization of the nonsinglet structure function $F_2$. We find $S_G=0.244\pm 0.045$, closer to the quark model expectation $S_G=\frac{1}{3}$ than previous results. We show that the uncertainty from the small $x$ region is somewhat underestimated in previous determinations.

A Higgs sextet is introduced in order to generate Dirac and Majorana neutrino masses in the 331 model with right-handed neutrinos. As will be seen the present sextet introduction leads to a rich neutrino mass structure. The smallness of neutrino masses can be achieved via, for example, a seesaw limit. The fact that the masses of the charged leptons are not effected by their new Yukawa couplings to the sextet is convenient for generating small neutrino masses.

Spontaneous Lorentz violation due to a time-dependent expectation value for a massless scalar has been suggested as a method for dynamically generating dark energy. A natural candidate for the scalar is a Goldstone boson arising from the spontaneous breaking of a $U(1)$ symmetry. We investigate the low-energy effective action for such a Goldstone boson in a general class of models involving only scalars, proving that if the scalars have standard kinetic terms then at the classical level the effective action does not have the required features for spontaneous Lorentz violation to occur asymptotically $(t\to \infty )$ in an expanding Friedman-Robertson-Walker universe. Then we study the large $N$ limit of a renormalizable field theory with a complex scalar coupled to massive fermions. In this model an effective action for the Goldstone boson with the properties required for spontaneous Lorentz violation can be generated. Although the model has shortcomings, we feel it represents progress towards finding a high energy completion for the Higgs phase of gravity.

We carry out a finite density calculation based on a canonical approach which is designed to address the overlap problem. Two degenerate flavor simulations are performed using Wilson gauge action and Wilson fermions on $4^4$ lattices, at temperatures close to the critical temperature $T_c\approx 170\mathrm{MeV}$ and large densities (5 to 20 times nuclear matter density). In this region, we find that the algorithm works well. We compare our results with those from other approaches.

The strong and electromagnetic decays of the ground-state tensor mesons are studied in an effective field approach. A fit to the well-known experimental data is performed. The decay ratios of the tensor glueball are evaluated and possible candidates are discussed.

We consider the bremsstrahlung and model-dependent contributions to the radiative decay ${\tau }^{-}\to {\pi }^{-}{\pi }^0{\nu }_{\tau }\gamma$ in the context of a meson dominance model. We focus on several observables related to this decay, including the branching ratio and the photon and di-pion spectra. Particular attention is paid to the sensitivity of different observables upon the effects of model-dependent contributions and of the magnetic dipole moment of the ${\rho }^{-}(770)$ vector meson. Important numerical differences are found with respect to results obtained in the framework of chiral perturbation theory.

We consider a holographic dark energy model, in which both the cosmological-constant (CC) energy density ${\rho }_{\Lambda }$ and the Newton constant $G_N$ are varying quantities, to study the problem of setting an effective field-theory IR cutoff. Assuming that ordinary matter scales canonically, we show that the continuity equation univocally fixes the IR cutoff, provided a law of variation for either ${\rho }_{\Lambda }$ or $G_N$ is known. Previous considerations on holographic dark energy disfavor the Hubble parameter as a candidate for the IR cutoff (for spatially flat universes), since in this case the ratio of dark energy to dark matter is not allowed to vary, thus hindering a deceleration era of the universe for the redshifts $z\gtrsim 0.5$. On the other hand, the future event horizon as a choice for the IR cutoff is being favored in the literature, although the “coincidence problem” usually cannot be addressed in that case. We extend considerations to spatially curved universes, and show that with the Hubble parameter as a choice for the IR cutoff one always obtains a universe that never accelerates or a universe that accelerates all the time, thus making the transition from deceleration to acceleration impossible. Next, we apply the IR cutoff consistency procedure to a renormalization-group (RG) running CC model, in which the low-energy variation of the CC is due to quantum effects of particle fields having masses near the Planck scale. We show that bringing such a model (having the most general cosmology for running CC universes) in full accordance with holography amounts to having such an IR cutoff which scales as a square root of the Hubble parameter. We find that such a setup, in which the only undetermined input represents the true ground state of the vacuum, can give early deceleration as well as late-time acceleration. The possibility of further improvement of the model is also briefly indicated.