We construct tree-level four-particle open-string amplitudes relevant to dilepton and diphoton production at hadron colliders. We expand the amplitudes into string resonance (SR) contributions and compare the total cross-section through the first SR with the $Z^{\prime }$ search at the Tevatron. We establish a current lower bound based on the CDF Run I results on the string scale to be about $1.1-2.1$ TeV, and it can be improved to about $1.5-3$  TeV with 2 ${\mathrm{f}\mathrm{b}}^{-1}$. At the LHC, we investigate the properties of signals induced by string resonances in dilepton and diphoton processes. We demonstrate the unique aspects of SR-induced signals distinguishable from other new physics, such as the angular distributions and forward-backward asymmetry. A $95\%$ C.L. lower bound can be reached at the LHC for $M_S>8.2-10$ TeV with an integrated luminosity of $300$ ${\mathrm{f}\mathrm{b}}^{-1}$. We emphasize the generic features and profound implications of the amplitude construction.

We consider supergravity with a gravitino lightest supersymmetric particle. The next-to-lightest supersymmetric particle (NLSP) decays to the gravitino with lifetime naturally in the range ${10}^4-{10}^8\mathrm{s}$. However, cosmological constraints exclude lifetimes at the upper end of this range and disfavor neutralinos as NLSPs, leaving charged sleptons with lifetimes below a year as the natural NLSP candidates. Decays to gravitinos may therefore be observed by trapping slepton NLSPs in water tanks placed outside Large Hadron Collider (LHC) and International Linear Collider (ILC) detectors and draining these tanks periodically to underground reservoirs where slepton decays may be observed in quiet environments. We consider 0.1, 1, and 10 kton traps and optimize their shape and placement. We find that the LHC may trap tens to thousands of sleptons per year. At the ILC, these results may be improved by an order of magnitude in some cases by tuning the beam energy to produce slow sleptons. Precision studies of slepton decays are therefore possible and will provide direct observations of gravitational effects at colliders; percent level measurements of the gravitino mass and Newton’s constant; precise determinations of the gravitino’s contribution to dark matter and supersymmetry breaking’s contribution to dark energy; quantitative tests of supergravity relations; and laboratory studies of Big Bang nucleosynthesis and cosmic microwave background phenomena.

We discuss reactor measurement of ${\theta }_{12}$ which has a potential of reaching the ultimate sensitivity which surpasses all the methods so far proposed. The key is to place a detector at an appropriate baseline distance from the reactor neutrino source to have an oscillation maximum at around a peak energy of the event spectrum in the absence of oscillation. By a detailed statistical analysis the optimal distance is estimated to be $\simeq (50-70)\mathrm{k}\mathrm{m}\times [8\times {10}^{-5}{\mathrm{e}\mathrm{V}}^2/\Delta m_{21}^2]$, which is determined by maximizing the oscillation effect in the event number distribution and minimizing geo-neutrino background contamination. To estimate possible uncertainty caused by surrounding nuclear reactors in distance of $\sim 100\mathrm{k}\mathrm{m}$, we examine a concrete example of a detector located at Mt. Komagatake, 54 km away from the Kashiwazaki-Kariwa nuclear power plant in Japan, the most powerful reactor complex in the world. The effect turns out to be small. Under a reasonable assumption of systematic error of 4% in the experiment, we find that ${sin}^2{\theta }_{12}$ can be determined to the accuracy of $\simeq 2\%(\simeq 3\%)$, at 68.27% CL for 1 degree of freedom, for $60{\mathrm{G}\mathrm{W}}_{\mathrm{t}\mathrm{h}}·\mathrm{k}\mathrm{t}\mathrm{o}\mathrm{n}·\mathrm{y}\mathrm{r}(20{\mathrm{G}\mathrm{W}}_{\mathrm{t}\mathrm{h}}·\mathrm{k}\mathrm{t}\mathrm{o}\mathrm{n}·\mathrm{y}\mathrm{r})$ operation. We also discuss implications of such an accurate measurement of ${\theta }_{12}$.

It is shown that the requirement of preservation of baryon asymmetry does not rule out a scale for leptogenesis as low as $10$ TeV. The conclusions are compatible with see-saw mechanism if, for example, the pivot mass scale for neutrinos is $\approx {10}^{-2}$ that of the charged leptons. We explore the parameter space ${\tilde{m}}_1$- $M_1$ of relevant light and heavy neutrino masses by solving Boltzmann equations. A viable scenario for obtaining baryogenesis in this way is presented in the context of gauged $B-L$ symmetry.

A simple quasiparticle model, motivated by lowest-order perturbative QCD, is proposed. It is applied to interpret the lattice QCD equation of state. A reasonable reproduction of the lattice data is obtained. In contrast to existing quasiparticle models, the present model is formulated in dynamical rather than thermodynamical terms, and is easily applicable to a system with finite baryon density. In particular, the model simulates the confinement property.

We investigate experiments that are sensitive to the scalar and parity-odd coefficients for Lorentz violation in the photon sector of the standard model extension (SME). We show that of the classic tests of special relativity, Ives-Stilwell (IS) experiments are sensitive to the scalar coefficient, but at only parts in ${10}^5$ for the state-of-the-art experiment. We then propose asymmetric Mach-Zehnder interferometers with different electromagnetic properties in the two arms, including recycling techniques based on travelling wave resonators to improve the sensitivity. With present technology we estimate that the scalar and parity-odd coefficients may be measured with a sensitivity better than parts in ${10}^{11}$ and ${10}^{15}$ respectively.

The energy-momentum vacuum average of a conformally coupled massless scalar field vibrating around a cosmic dislocation—a cosmic string with a dislocation along its axis—is taken as source of the linearized semiclassical Einstein equations. The solution up to first order in the Planck constant is derived. Motion of a test particle is then discussed, showing that under certain circumstances a helical-like dragging effect, with no classical analogue around the cosmic dislocation, is induced by backreaction.

Type Ia supernova data have recently become strong enough to enable, for the first time, constraints on the time variation of the dark energy density and its equation of state. Most analyses, however, are using simple two or three-parameter descriptions of the dark energy evolution, since it is well known that allowing more degrees of freedom introduces serious degeneracies. Here we present a method to produce uncorrelated and nearly model-independent band power estimates of the equation of state of dark energy and its density as a function of redshift. We apply the method to recently compiled supernova data. Our results are consistent with the cosmological constant scenario, in agreement with other analyses that use traditional parametrizations, though we find marginal (2-$\sigma$) evidence for $w(z)<-1$ at $z<0.2$. In addition to easy interpretation, uncorrelated, localized band powers allow intuitive and powerful testing of the constancy of either the energy density or equation of state. While we have used relatively coarse redshift binning suitable for the current set of $\sim 150$ supernovae, this approach should reach its full potential in the future, when applied to thousands of supernovae found from ground and space, combined with complementary information from other cosmological probes.

Motivated by a recent detection of 511 keV photons from the center of our Galaxy, we calculate the spectrum of the soft $\gamma$-ray background of the redshifted 511 keV photons from cosmological halos. Annihilation of dark matter particles into electron-positron pairs makes a substantial contribution to the $\gamma$-ray background. Mass of such dark matter particles must be $\lesssim 100\mathrm{M}\mathrm{e}\mathrm{V}$ so that resulting electron-positron pairs are nonrelativistic. On the other hand, we show that in order for the annihilation not to exceed the observed background, the dark matter mass needs to be $\gtrsim 20\mathrm{M}\mathrm{e}\mathrm{V}$. We include the contribution from the active galactic nuclei and supernovae. The halo substructures may increase the lower bound to $\gtrsim 60\mathrm{M}\mathrm{e}\mathrm{V}$.

This work analyzes hadronic decays of exotic mesons, with a focus on the lightest one, the $J^{PC}=1^{-+}$ ${\pi }_1$, in a fully relativistic formalism, and makes comparisons with nonrelativistic results. We also discuss Coulomb gauge decays of normal mesons that proceed through their hybrid components. The relativistic spin wave functions of mesons and hybrids are constructed based on unitary representations of the Lorentz group. The radial wave functions are obtained from phenomenological considerations of the mass operator. Fully relativistic results (with Wigner rotations) differ significantly from nonrelativistic ones. We also find that the decay channels ${\pi }_1\to \pi b_1,\pi f_1,K{K}_1$ are favored, in agreement with results obtained using other models.

We perform a systematic analysis on the off-forward matrix elements of the twist-two quark and gluon helicity-flip operators. By matching the allowed quantum numbers and their crossing channel counterparts (a method developed by Ji and Lebed), we systematically count the number of independent nucleon form factors in off-forward scattering of matrix elements of these quark and gluon spin-flip operators. In particular, we find that the numbers of independent nucleon form factors of twist-two, helicity-flip quark (gluon) operators are $2n-1$ ($2n-5$) if $n$ is odd, and $2n-2$ ($2n-6$) if $n$ is even, with $n\ge 2$ ($n\ge 4$). We also analyze and write down the tensorial/Lorentz structure and kinematic factors of the expansion of these operators' matrix elements in terms of the independent form factors. These generalized form factors define the off-forward quark and gluon helicity-flip distributions in the literature.

In this paper we increase the minimal supersymmetric standard model tree level Higgs mass bound to a value that is naturally larger than the LEP-II search constraint by adding to the superpotential a $\lambda S{H}_u{H}_d$ term, as in the next to minimal supersymmetric standard model, and UV completing with new strong dynamics before $\lambda$ becomes nonperturbative. Unlike other models of this type, the Higgs fields remain elementary, alleviating the supersymmetric fine-tuning problem while maintaining unification in a natural way.

Recent developments provided evidence that the dimension 2 gluon condensate $⟨A^2⟩$ is important for the nonperturbative regime of Yang-Mills theories (quantized in the Landau gauge). We show that it may be relevant for the Dyson-Schwinger approach to QCD. In order that this approach leads to a successful hadronic phenomenology, an enhancement of the effective quark-gluon interaction seems to be needed at intermediate ($p^2\sim 0.5{\mathrm{G}\mathrm{e}\mathrm{V}}^2$) momenta. It is shown that the gluon condensate $⟨A^2⟩$ provides such an enhancement. It is also shown that the resulting effective strong running coupling leads to the sufficiently strong dynamical chiral symmetry breaking and successful phenomenology at least in the light sector of pseudoscalar mesons.

We study the effects of including a running coupling constant in high-density QCD evolution. For fixed coupling constant, QCD evolution preserves the initial dependence of the saturation momentum $Q_s$ on the nuclear size $A$ and results in an exponential dependence on rapidity $Y$, $Q_s^2(Y)=Q_s^2(Y_0)\exp [{\overline{\alpha }}_{s}d(Y-Y_0)]$. For the running coupling case, we rederive analytical estimates for the $A$ and $Y$ dependences of the saturation scale and test them numerically. The $A$ dependence of $Q_s$ vanishes $\propto 1/\sqrt{Y}$ for large $A$ and $Y$. The $Y$ dependence is reduced to $Q_s^2(Y)\propto \exp ({\Delta }^{\prime }\sqrt{Y+X})$, where we find numerically ${\Delta }^{\prime }\simeq 3.2$. We study the behavior of the gluon distribution at large transverse momentum, characterizing it by an anomalous dimension $1-\gamma$, which we define in a fixed region of small dipole sizes. In contrast to previous analytical work, we find a marked difference between the fixed coupling ($\gamma \simeq 0.65$) and running coupling ($\gamma \sim 0.85$) results. Our numerical findings show that both a scaling function depending only on the variable $r{Q}_s$ and the perturbative double-leading-logarithmic expression provide equally good descriptions of the numerical solutions for very small $r$ values below the so-called scaling window.

In the context of supersymmetric theories, a weakly broken gauged SO(3) flavor symmetry is used to produce two highly degenerate right-handed neutrinos. It is then shown that this SO(3) flavor symmetry is compatible with all fermion masses and mixings if it is supplemented with a further SU(3) flavor symmetry. A specific supersymmetry breaking model is used to generate the light neutrino masses as well as a natural model of TeV scale resonant leptogenesis.

Various approaches to black hole entropy yield the area law with logarithmic corrections, many involving a coefficient $1/2$, and some involving $3/2$. It is pointed out here that the standard quantum geometry formalism with spin one-half at each puncture is not consistent with $3/2$.

We propose a duality between the large-$N$ gauged harmonic oscillator and a novel string theory in two dimensions.

Classical $\mathcal{N}=4$ Yang-Mills theory is defined by the superspace constraints. We obtain a solution of a subset of these constraints and show that it leads to the maximally helicity violating amplitudes. The action which leads to the solvable part of the constraints is a Wess-Zumino-Witten action on a suitably $extended$ superspace. The non-maximally helicity violating tree amplitudes can also be expressed in terms of this action.

We consider tunneling transitions between states separated by an energy barrier in a simple field theoretical model. We analyze the case of soliton creation induced by collisions of a few highly energetic particles. We present a semiclassical, but otherwise first principle, study of this process at all energies of colliding particles. We find that direct tunneling to the final state occurs at energies below the critical value $E_c$, which is slightly higher than the barrier height. Tunneling probability grows with energy in this regime. Above the critical energy, the tunneling mechanism is different. The transition proceeds through creation of a state close to the top of the potential barrier (sphaleron) and its subsequent decay. At a certain limiting energy, $E_l$, tunneling probability ceases to grow. At higher energies, the dominant mechanism of transition becomes the release of energy excess $E-E_l$ by the emission of a few particles and then tunneling at effectively lower energy $E=E_l$ via the limiting semiclassical configuration. The latter belongs to a class of “real-time instantons,” semiclassical solutions saturating the inclusive probability of tunneling from initial states with a given number of particles. We conclude that the process of collision-induced tunneling is exponentially suppressed at all energies.

Continuing previous work on the 3PN-accurate gravitational-wave generation from point-particle binaries, we obtain the binary’s 3PN mass-type quadrupole and dipole moments for general (not necessarily circular) orbits in harmonic coordinates. The final expressions are given in terms of their core parts, resulting from the application of the pure-Hadamard-Schwartz self-field regularization scheme, and augmented by an ambiguous part. In the case of the 3PN quadrupole we find three ambiguity parameters, $\xi$, $\kappa$ and $\zeta$, but only one for the 3PN dipole, in the form of the particular combination $\xi +\kappa$. Requiring that the dipole moment agree with the center-of-mass position deduced from the 3PN equations of motion in harmonic coordinates yields the relation $\xi +\kappa =-9871/9240$. Our results will form the basis of the complete calculation of the 3PN radiation field of compact binaries by means of dimensional regularization.