A detailed analysis of vacuum Cherenkov radiation in spacelike Maxwell-Chern-Simons (MCS) theory is presented. A semiclassical treatment reproduces the leading terms of the tree-level result from quantum field theory. Moreover, certain quantum corrections turn out to be suppressed for large energies of the charged particle, for example, the quantum corrections to the classical MCS Cherenkov angle. It is argued that MCS-theory Cherenkov radiation may, in principle, lead to anisotropy effects for ultra-high-energy cosmic rays (UHECRs). In addition, a qualitative discussion of vacuum Cherenkov radiation from a modified-Maxwell term in the action is given, together with UHECR bounds on some of its dimensionless “coupling constants.”

We reanalyze leptogenesis via the out-of-equilibrium decay of the lightest right-handed neutrino in type II seesaw scenarios, taking into account flavor-dependent effects. In the type II seesaw mechanism, in addition to the type I seesaw contribution, an additional direct mass term for the light neutrinos is present. We consider type II seesaw scenarios where this additional contribution arises from the vacuum expectation value of a Higgs triplet, and furthermore an effective model-independent approach. We investigate bounds on the flavor-specific decay asymmetries, on the mass of the lightest right-handed neutrino and on the reheat temperature of the early universe, and compare them to the corresponding bounds in the type I seesaw framework. We show that while flavor-dependent thermal type II leptogenesis becomes more efficient for larger mass scale of the light neutrinos, and the bounds become relaxed, the type I seesaw scenario for leptogenesis becomes more constrained. We also argue that in general, flavor-dependent effects cannot be ignored when dealing with leptogenesis in type II seesaw models.

Rotating black hole solutions in the $(3+1)$-dimensional Chern-Simons modified gravity theory are discussed by taking account of perturbation around the Schwarzschild solution. The zenith-angle dependence of a metric function related to the frame-dragging effect is determined from a constraint equation independently of a choice of the embedding coordinate. We find that at least within the framework of the first-order perturbation method, the black hole cannot rotate for finite black hole mass if the embedding coordinate is taken to be a timelike vector. However, the rotation can be permitted in the limit of $M/r\to 0$ (where $M$ is the black hole mass and $r$ is the radius). For a spacelike vector, the rotation can also be permitted for any value of the black hole mass.

The effect of variations of the fundamental nuclear parameters on big-bang nucleosynthesis are modeled and discussed in detail taking into account the interrelations between the fundamental parameters arising in unified theories. Considering only ${}^4\mathrm{He}$, strong constraints on the variation of the neutron lifetime, neutron-proton mass difference are set. These constraints are then translated into constraints on the time variation of the Yukawa couplings and the fine structure constant. Furthermore, we show that a variation of the deuterium binding energy is able to reconcile the ${}^7\mathrm{Li}$ abundance deduced from the WMAP analysis with its spectroscopically determined value while maintaining concordance with D and ${}^4\mathrm{He}$. The analysis is strongly based on the potential model of Flambaum and Shuryak that relates the binding energy of the deuteron with the nucleon and $\sigma$ and $\omega$ mesons masses; however, we show that an alternative approach that consists of a pion mass dependence necessarily leads to equivalent conclusions.

Recently, Higgsless models have proven to be viable alternatives to the standard model (SM) and supersymmetric models in describing the breaking of the electroweak symmetry. Whether extra dimensional in nature or their deconstructed counterparts, the physical spectrum of these models typically consists of towers of massive vector gauge bosons which carry the same quantum numbers as the SM $W$ and $Z$. In this paper, we calculate the one-loop, chiral-logarithmic corrections to the $S$ and $T$ parameters from the lightest (i.e. SM) and the next-to-lightest gauge bosons using a novel application of the pinch technique. We perform our calculation using generic Feynman rules with generic couplings such that our results can be applied to various models. To demonstrate how to use our results, we calculate the leading chiral-logarithmic corrections to the $S$ and $T$ parameters in the deconstructed three-site Higgsless model. As we point out, however, our results are not exclusive to Higgsless models and may, in fact, be used to calculate the one-loop corrections from additional gauge bosons in models with fundamental (or composite) Higgs bosons.

The $D{\overline{D}}^{*}$ scattering amplitude and the production of the final states ${\pi }^{+}{\pi }^{-}J/\psi$ and ${\pi }^{+}{\pi }^{-}{\pi }^{0}J/\psi$ near the $D^0{\overline{D}}^{*0}$ threshold are discussed following the recent suggestion that the observed peaks $X(3872)$ and $X(3875)$ in the decays $B\to XK$ are due to a virtual state $X$ in the $D^0{\overline{D}}^{*0}$ channel. The strong interaction is treated using the small interaction radius approximation. It is shown that the mass difference between the charged and neutral $D^{(*)}$ mesons results in a distinctive behavior of the relevant isotopic amplitudes. In particular, the shape of the peak in the ${\pi }^{+}{\pi }^{-}J/\psi$ channel should be significantly narrower than in the ${\pi }^{+}{\pi }^{-}{\pi }^{0}J/\psi$ channel, which property can be used for an experimental test of the virtual state hypothesis.

The IceCube neutrino detector is a cubic kilometer TeV to PeV neutrino detector under construction at the geographic South Pole. The dominant population of neutrinos detected in IceCube is due to meson decay in cosmic-ray air showers. These atmospheric neutrinos are relatively well understood and serve as a calibration and verification tool for the new detector. In 2006, the detector was approximately 10% completed, and we report on data acquired from the detector in this configuration. We observe an atmospheric neutrino signal consistent with expectations, demonstrating that the IceCube detector is capable of identifying neutrino events. In the first 137.4 days of live time, 234 neutrino candidates were selected with an expectation of $211\pm 76.1(\mathrm{syst})\pm 14.5(\mathrm{stat})$ events from atmospheric neutrinos.

We propose a recipe to construct the discrete light-cone quantization (DLCQ) Hamiltonian of type IIB string theory on the anti-de Sitter (AdS) (and/or plane-wave) background. We consider a system of $J$ number of coincident unstable non-Bogomol’nyi-Prasad-Sommerfield (BPS) D0 branes of IIB theory in the light-cone gauge and on the plane-wave background with a compact null direction, the dynamics of which is described by the worldline $U(J)$ gauge theory. This configuration suffers from tachyonic instabilities. Having instabilities be cured through the process of open string tachyon condensation, by expanding the theory about true minima of the effective potential and furthermore taking the low energy limit to decouple the heavy modes, we end up with a $0+1$-dimensional supersymmetric $U(J)$ gauge theory, a matrix theory. We conjecture that the Hamiltonian of this matrix theory is just the DLCQ Hamiltonian of type IIB string theory on the AdS or equivalently plane-wave background in a sector with $J$ units of light-cone momentum. We present some pieces of evidence in support of the proposal.

We consider $\mathcal{N}=4$ supersymmetric Yang-Mills theory with $SU(N)$ gauge group at large $N$ and at finite temperature on a spatial $S^3$. We show that, at finite weak ’t Hooft coupling, a sector of the theory is naturally described as a two-dimensional Coulomb gas of complex eigenvalues, ${\Phi }_J+i{A}_0$, valued on the cylinder. In the low temperature confined phase the eigenvalues condense onto a strip encircling the cylinder, while the high temperature deconfined phase is characterized by an ellipsoidal droplet of eigenvalues.

We calculate photon production from a quark-gluon plasma which is anisotropic in momentum space including the Compton scattering, $q(\overline{q})g\to q(\overline{q})\gamma$, and annihilation, $q\overline{q}\to g\gamma$, processes. We show that for a quark-gluon plasma which has an oblate momentum-space anisotropy, $⟨p_L^2⟩<⟨p_T^2⟩$, the photon production rate has an angular dependence which is peaked transverse to the beam line. We propose to use the angular dependence of high-energy medium photon production to experimentally determine the degree of momentum-space isotropy of a quark-gluon plasma produced in relativistic heavy-ion collisions.

We investigate one of the consequences of the twisted Poincaré symmetry. We derive the charge conservation law and show that the equivalence principle is satisfied in the canonical noncommutative spacetime. We applied the twisted Poincaré symmetry to Weinberg’s analysis [S. Weinberg, Phys. Rev. 135, B1049 (1964).]. To this end, we generalize our earlier construction of the twisted $S$ matrix [J. G. Bu, H. C. Kim, Y. Lee, C. H. Vac, and J. H. Yee, Phys. Rev. D 73, 125001 (2006).], which applies the noncommutativity to the Fourier modes, to the massless fields of integer spins. The transformation formula for the twisted $S$ matrix for the massless fields of integer spin has been obtained. For massless fields of spin 1, we obtain the conservation of charge, and the universality of the coupling constant for massless fields of spin 2, which can be interpreted as the equality of gravitational mass and inertial mass, i.e., the equivalence principle.

In this work, the behavior of test particles near a domain wall of a stable false vacuum bubble is studied. It is shown that matter is naturally trapped in the vicinity of a static domain wall, and also, that there is a discontinuity in the test particle’s velocity when crossing the domain wall. The latter is unexpected as it stands in contrast to Newtonian theory, where infinite forces are not allowed. The weak field limit is defined in order to show that there is no conflict with the nonrelativistic behavior of gravitational fields and particle motions under these conditions.

The Bethe-Salpeter equation is related to a generalized quantum-mechanical Hamiltonian. Instability of the presumed vacuum, indicated by a tachyon, is related to a negative energy eigenstate of this Hamiltonian. The variational method shows that an arbitrarily weak long-range attraction leads to chiral symmetry breaking, except in the scale-invariant case when the instability occurs at a critical value of the coupling. In the case of short-range attraction, an upper bound for the critical coupling is obtained.

The chiral anomaly in the context of an extended standard model with Lorentz invariance violation is studied. Taking into account bounds from measurements of the speed of light, we argue that the chiral anomaly and its consequences are general results valid even beyond the relativistic symmetry.

In quantum information theory, it is well known that the tripartite entanglement of three qubits is described by the group $[SL(2,C){]}^3$ and that the entanglement measure is given by Cayley’s hyperdeterminant. This has provided an analogy with certain $N=2$ supersymmetric black holes in string theory, whose entropy is also given by the hyperdeterminant. In this paper, we extend the analogy to $N=8$. We propose that a particular tripartite entanglement of seven qubits, encoded in the Fano plane, is described by the exceptional group $E_7(C)$ and that the entanglement measure is given by Cartan’s quartic $E_7$ invariant.

The four-dimensional $N=2$ $STU$ model of string compactification is invariant under an $SL(2,Z{)}_S\times SL(2,Z{)}_T\times SL(2,Z{)}_U$ duality acting on the dilaton/axion $S$, complex Kahler form $T$, and the complex structure fields $U$, and also under a string/string/string triality $S\leftrightarrow T\leftrightarrow U$. The model admits an extremal black hole solution with four electric and four magnetic charges whose entropy must respect these symmetries. It is given by the square root of the hyperdeterminant introduced by Cayley in 1845. This also features three-qubit quantum entanglement.

We derive the mass-radius relation of relativistic white dwarf stars (modeled as a self-gravitating degenerate Fermi gas at $T=0$) in a $D$-dimensional universe and study the influence of the dimension of space on the laws of physics when we combine quantum mechanics, special relativity, and gravity. We exhibit characteristic dimensions $D=1$, $D=2$, $D=3$, $D=(3+\sqrt{17})/2$, $D=4$, $D=2(1+\sqrt{2})$ and show that quantum mechanics cannot balance gravitational collapse for $D\ge 4$. This is similar to a result found by Ehrenfest (1917) at the atomic level for Coulomb forces (in Bohr’s model) and for the Kepler problem. This makes the dimension of our universe $D=3$ very particular with possible implications regarding the anthropic principle. We discuss some historic aspects concerning the discovery of the Chandrasekhar (1931) limiting mass in relation to previous investigations by Anderson (1929) and Stoner (1930). We also propose different derivations of the stability limits of polytropic distributions and consider their application to classical and relativistic white dwarf stars.

We study lepton flavor violating analogs of the photoelectric effect, with a final $\mu$ or $\tau$ instead of an electron: $\gamma e\to \mu$ and $\gamma e\to \tau$. On the basis of the general parametrization of the matrix element of the electromagnetic current we estimate the upper limits for the cross sections and event rates of these processes, imposed by the current experimental bounds on $\mu \to e\gamma$ and $\tau \to e\gamma$ decays.

The minimal supersymmetric SO(10) grand unified theory (GUT) models with $\mathbf{10}$, $\mathbf{126}$, and $\mathbf{210}$ Higgs and only renormalizable couplings have been shown to provide a simple way to understand the neutrino mixings as well as the ratio $\Delta m_{\odot }^2/\Delta m_A^2$ in terms of quark mixing parameter ${\theta }_{\mathrm{Cabibbo}}$, provided neutrino masses are described by a type II seesaw formula. However, in this minimal picture, it is impossible to realize type II dominance with renormalizable couplings in 4 dimensions. We show that this problem can be cured by embedding this model into a warped five dimensional space-time with warping between the Planck and the GUT scale, where both type II as well as mixed seesaw formulas can be realized in a natural manner without expanding the Higgs sector. These models also avoid the possible problem of threshold effects associated with large Higgs representations since the theory above the GUT scale is now strongly coupled.

We calculate modifications to the scalar Casimir force between two parallel plates due to space-time noncommutativity. We devise a heuristic approach to overcome the difficulties of describing boundaries in noncommutative theories and predict that boundary corrections are of the same order as noncommutative volume corrections. Further, both corrections have the form of more conventional finite surface effects.