The photon spectrum in orthopositronium $\to 3\gamma$ decay is computed using effective field theory methods. For energetic photons, the spectrum agrees with the Ore-Powell result, but deviates from it when the photon energy is comparable to the positronium binding energy. The decay spectrum in this region depends on a positronium structure function, which is computed in this paper. At still lower energies the photon spectrum is dominated by the parapositronium resonance contribution. Our results are compatible with Low’s theorem on soft photon emission.

We present 90% confidence level limits on magnetic monopole production at the Fermilab Tevatron from three sets of samples obtained from the D0 and CDF detectors each exposed to a proton-antiproton luminosity of $\sim 175{\mathrm{pb}}^{-1}$ (experiment E-882). Limits are obtained for the production cross sections and masses for low-mass accelerator-produced pointlike Dirac monopoles trapped and bound in material surrounding the D0 and CDF collision regions. In the absence of a complete quantum field theory of magnetic charge, we estimate these limits on the basis of a Drell-Yan model. These results (for magnetic charge values of 1, 2, 3, and 6 times the minimum Dirac charge) extend and improve previously published bounds.

We propose that quarks and leptons are interchangeable entities in the high-energy limit. This naturally results in the extension of $\left[\mathrm{SU}\right(3)\mathrm{}{]}^3$ trinification to $\left[\mathrm{SU}\right(3)\mathrm{}{]}^4$ quartification. In addition to the unbroken color ${\mathrm{SU}\left(3\right)\mathrm{}}_q$ of quarks, there is now also a color ${\mathrm{SU}\left(3\right)\mathrm{}}_l$ of leptons which reduces to an unbroken ${\mathrm{SU}\left(2\right)\mathrm{}}_l.$ We discuss the natural occurrence of ${\mathrm{SU}\left(2\right)\mathrm{}}_l$ doublets at the TeV energy scale, which leads remarkably to the unification of all gauge couplings without supersymmetry. Proton decay occurs through the exchange of scalar bosons, with a lifetime in the range ${10}^{34}–{10}^{36}$ yr.

The thermal instability of the giant graviton is investigated within the Berenstein-Maldacena-Nastase (BMN) matrix model. We calculate the one-loop thermal correction of the quantum fluctuation around the trivial vacuum and giant graviton, respectively. From the exact formula of the free energy we see that at low temperature the giant graviton is unstable and will dissolve into vacuum fluctuations. However, at sufficiently high temperature the trivial vacuum fluctuation will condense to form the giant graviton configuration. The transition temperature of the giant graviton is determined in our calculation.

We compute the leading-order collisional energy loss of a heavy fermion propagating in a QED plasma with an electron distribution function which is anisotropic in momentum space. We show that in the presence of such anisotropies there can be a significant directional dependence of the heavy fermion energy loss with the effect being large for highly relativistic velocities. We also repeat the analysis of the isotropic case more carefully and show that the final result depends on the intermediate scale used to separate hard and soft contributions to the energy loss. We then show that the canonical isotropic result is obtained in the weak-coupling limit. For intermediate coupling we use the residual scale dependence as a measure of our theoretical uncertainty. We also discuss complications which could arise due to the presence of unstable soft photonic modes and demonstrate that the calculation of the energy loss is safe.

The unification of quantum field theory and general relativity is a fundamental goal of modern physics. In many cases, theoretical efforts to achieve this goal introduce auxiliary gravitational fields, ones in addition to the familiar symmetric second-rank tensor potential of general relativity, and lead to nonmetric theories because of direct couplings between these auxiliary fields and matter. Here, we consider an example of a metric-affine gauge theory of gravity in which torsion couples nonminimally to the electromagnetic field. This coupling causes a phase difference to accumulate between different polarization states of light as they propagate through the metric-affine gravitational field. Solar spectropolarimetric observations are reported and used to set strong constraints on the relevant coupling constant k: $k^2<(2.5\mathrm{}\mathrm{km}{)}^2.$

We study the possibility of measuring nonstandard CP violation effects through a Dalitz plot analysis in $B^{\pm }\to D_s^{\pm }{D}^0{\pi }^0$ decays. The accuracy in the extraction of CP violating phases is analyzed by performing a Monte Carlo simulation of the decays, and the magnitude of possible new physics effects is discussed. It is found that this represents a hopeful scenario for the search for new physics.

We use the NRQCD factorization formalism to calculate the relativistic corrections to the fragmentation function for a gluon fragmenting into a spin-triplet S-wave heavy quarkonium. We make use of the gauge-invariant formulation of the fragmentation function of Collins and Soper. The color-octet contribution receives a large, negative relativistic correction, while the color-singlet contribution receives a large, positive relativistic correction. The considerable decrease in the color-octet contribution requires a corresponding increase in the phenomenological value of the leading color-octet matrix element in order to maintain a fit to the Fermilab Tevatron data.

We propose that the search of the $\overrightarrow{B}{D}_{\mathrm{sJ}}^{*}M$ decays, $M=D,$ $\pi ,$ and K, can discriminate the different theoretical postulations for the nature of the recently observed $D_{\mathrm{sJ}}^{*}$ mesons. The ratio of the branching ratios $B\left(\overrightarrow{B}{D}_{\mathrm{sJ}}^{*}M\right)/B\left(\overrightarrow{B}{D}_s^{\left(*\right)}M\right)\approx 1$ (0.1) supports that the $D_{\mathrm{sJ}}^{*}$ mesons are quark-antiquark (multiquark) bound states. The Belle measurement of the $\overrightarrow{B}{D}_{\mathrm{sJ}}^{*}D$ branching ratios seems to indicate an unconventional picture.

We systematically investigate the embedding of ${U\left(1\right)\mathrm{}}_X$ Froggatt-Nielsen models in (four-dimensional) local supersymmetry. We restrict ourselves to models with a single flavon field. We do not impose a discrete symmetry by hand, e.g., R parity, baryon parity, or lepton parity. Thus we determine the order of magnitude of the baryon- and/or lepton-violating coupling constants through the Froggatt-Nielsen scenario. We then scrutinize whether the predicted coupling constants are in accord with weak or GUT scale constraints. Many models turn out to be incompatible.

We compute the moduli Kähler potential for M theory on a compact manifold of $G_2$ holonomy in a large radius approximation. Our method relies on an explicit $G_2$ structure with small torsion, its periods and the calculation of the approximate volume of the manifold. As a verification of our result, some of the components of the Kähler metric are computed directly by integration over harmonic forms. We also discuss the modification of our result in the presence of codimension-four singularities and derive the gauge-kinetic functions for the massless gauge fields that arise in this case.

We consider the compactification of $\mathrm{}(d+n)\mathrm{}$-dimensional pure gravity and of superstring or M-theory on an n-dimensional internal space to a d-dimensional Friedmann-Lemaître-Robertson-Walker (FLRW) cosmology, with a spatial curvature $k=0,\pm 1,$ in the Einstein conformal frame. The internal space is taken to be a product of Einstein spaces, each of which is allowed to have arbitrary curvature and a time-dependent volume. By investigating the effective d-dimensional scalar potential, which is a sum of exponentials, it is shown that such compactifications, in the $k=0,+1\mathrm{}$ cases, do not lead to large amounts of accelerating expansion of the scale factor of the resulting FLRW universe, and, in particular, do not lead to inflation. The case $k=-1$ admits solutions with eternal accelerating expansion for which the acceleration, however, tends to zero at late times.

In the context of the imaginary-time formalism for scalar thermal field theory, it is shown that the result of performing the summations over Matsubara frequencies associated with loop Feynman diagrams can be written, for some classes of diagrams, in terms of the action of a simple linear operator on the corresponding energy integrals of the Euclidean theory at $T=0.\mathrm{}$ In its simplest form this operator depends only on the number of internal propagators of the graph. More precisely, it is shown explicitly that this “thermal operator representation” holds for two generic classes of diagrams: namely, the two-vertex diagram with an arbitrary number of internal propagators and the one-loop diagram with an arbitrary number of vertices. The validity of the thermal operator representation for diagrams of more complicated topologies remains an open problem. Its correctness is shown to be equivalent to the correctness of some diagrammatic rules proposed a few years ago.

We consider the brane-world generalization of the Gödel universe and analyze its dynamical interaction with the bulk. The exact homogeneity of the standard Gödel spacetime no longer holds, unless the bulk is also static. We show how the anisotropy of the Gödel-type brane is dictated by that of the bulk and find that the converse is also true. This determines the precise evolution of the nonlocal anisotropic stresses, without any phenomenological assumptions, and leads to a self-consistent closed set of equations for the evolution of the Gödel brane. We also examine the causality of the Gödel brane and show that the presence of the bulk cannot prevent the appearance of closed time-like curves.

Because of the Unruh effect, accelerated and inertial observers differ in their description of a given quantum state. The implications of this effect are explored for the entropy assigned by such observers to localized objects that may cross the associated Rindler horizon. It is shown that the assigned entropies differ radically in the limit where the number of internal states n becomes large. In particular, the entropy assigned by the accelerated observer is a bounded function of n. General arguments are given along with explicit calculations for free fields. The implications for discussions of the generalized second law and proposed entropy bounds are also discussed.

We use big bang nucleosynthesis calculations and light element abundance data to constrain the relative variation of the deuteron binding energy since the Universe was a few minutes old, $\delta Q=Q\left(\mathrm{BBN}\right)\mathrm{}-Q\left(\mathrm{present}\right).\mathrm{}$ Two approaches are used, first treating the baryon to photon ratio $\eta$ as a free parameter, but with the additional freedom of varying $\delta Q,$ and second using the WMAP value of $\eta$ and solving only for $\delta Q.\mathrm{}$ Including varying Q yields a better fit to the observational data than imposing the present day value, rectifying the discrepancy between the ${}^4\mathrm{He}$ abundance and the deuterium and ${}^7\mathrm{Li}$ abundances, and yields good agreement with the independently determined ${\eta }_{\mathrm{WMAP}}.$ Using ${\eta }_{\mathrm{WMAP}},$ the minimal deviation consistent with the data is significant at about the $4\sigma$ level; $\delta Q/Q=-0.019\pm \mathrm{0.005.}$ If the primordial ${}^4\mathrm{He}$ abundance lies towards the low end of values in the literature, this deviation is even larger and more statistically significant. Taking the light element abundance data at face value, our result may be interpreted as variation of the dimensionless ratio ${X=m}_s/{\Lambda }_{\mathrm{QCD}}$ of the strange quark mass and strong scale: $\delta X/X=(1.1\mathrm{}\pm 0.3)\times {10}^{-3}.$ These results provide a strong motivation for a more thorough exploration of the potential systematic errors in the light element abundance data.

In addition to generating the appropriate perturbation power spectrum, an inflationary scenario must take into account the need for inflation to end subsequently. In the context of single-field inflation models where inflation ends by breaking the slow-roll condition, we constrain the first and second derivatives of the inflaton potential using this additional requirement. We compare this with current observational constraints from the primordial spectrum and discuss several issues relating to our results.

We study the curvaton scenario in the supersymmetric framework, paying particular attention to the fact that scalar fields are inevitably complex in supersymmetric theories. If there is more than one scalar field associated with the curvaton mechanism, isocurvature (entropy) fluctuations between those fields in general arise, which may significantly affect the properties of the cosmic density fluctuations. We examine several candidates for the curvaton in the supersymmetric framework, such as moduli fields, the Affleck-Dine field, F- and D-flat directions, and the right-handed sneutrino. We estimate how the isocurvature fluctuations generated in each case affect the cosmic microwave background angular power spectrum. With the use of a recent observational result of the WMAP, stringent constraints on the models are derived and, in particular, it is seen that a large fraction of the parameter space is excluded if the Affleck-Dine field plays the role of the curvaton field. Natural and well-motivated candidates of the curvaton are also listed.

We perform a generalized analysis of data from WIMP search experiments for pointlike WIMPs of arbitrary spin and general Lorenz-invariant WIMP-nucleus interaction. We explicitly show that in the nonrelativistic limit only spin-independent (SI) and spin-dependent (SD) WIMP-nucleon interactions survive, which can be parametrized by only five independent parameters. We explore this five-dimensional parameter space to determine whether the annual modulation observed in the DAMA experiment can be consistent with all other experiments which reported null results. The pure SI interaction is ruled out except for a very small region of parameter space with the WIMP mass close to 50 GeV and the ratio of the WIMP-neutron to WIMP-proton SI couplings $-0.77<~f_n{/f}_p<~-\mathrm{0.75.}$ For the predominantly SD interaction, we find an upper limit on the WIMP mass of about 18 GeV, which can only be weakened if the constraint stemming from null searches for energetic neutrinos from WIMP annihilation the Sun is evaded. None of the regions of the parameter space that can reconcile all WIMP search results can be easily accommodated in the minimal supersymmetric standard model.

The standard model provides an excellent description of the observables measured at high energy lepton and hadron colliders. However, measurements of the forward-backward asymmetry of the bottom quark at CERN LEP suggest that the effective coupling of the right-handed bottom quark to the neutral weak gauge boson is significantly different from the value predicted by the standard model. Such a large discrepancy may be the result of a mixing of the bottom quark with heavy mirror fermions with masses of the order of the weak scale. To be consistent with the precision electroweak data, the minimal extension of the standard model requires the presence of vector-like pairs of $\mathrm{SU}\left(2\right)\mathrm{}$ doublet and singlet quarks. In this article, we show that such an extension of the standard model is consistent with the unification of gauge couplings and leads to a very rich phenomenology at the Fermilab Tevatron, the B factories and the CERN LHC. In particular, if the Higgs boson mass lies in the range $120\mathrm{GeV}\lesssim m_h\lesssim 180\mathrm{GeV},$ we show that run II of the Tevatron collider with $4–8{\mathrm{fb}}^{-1}$ of integrated luminosity will have the potential to discover the heavy quarks, while observing $3\sigma$ evidence of the Higgs boson in most of the parameter space.