We study the effect of interference between the standard model Higgs boson resonance and the continuum background in the process $\gamma \gamma \to H\to b\overline{b}$ at a photon collider. Taking into account virtual gluon exchange between the final-state quarks, we calculate the leading corrections to the height of the resonance for the case of a light ($m_H<160\mathrm{GeV}$) Higgs boson. We find that the interference is destructive and around 0.1%–0.2% of the peak height, depending on the mass of the Higgs and the scattering angle. This suppression is smaller by an order of magnitude than the anticipated experimental accuracy at a photon collider. However, the fractional suppression can be significantly larger if the Higgs coupling to $b$ quarks is increased by physics beyond the standard model.

We discuss the role of $F$-term uplifting in stabilizing moduli within the framework of heterotic string theory. It turns out that the uplifting sector plays an important role in fixing the volume modulus at one of the self-dual points of a modular invariant potential. For the volume modulus stabilized at a self-dual point, the $F$-term uplifting leads to the dilation stabilization which can naturally yield the mirage mediation pattern of soft supersymmetry breaking terms. Generalizing to the case with anomalous $U(1)$ gauge symmetry, we also find that the $U(1)$ sector generically gives a contribution to sfermion masses comparable to the dilaton-mediated one while maintaining the mirage mediation pattern.

We study the duality cascade of softly broken supersymmetric theories. We investigate the renormalization group (RG) flow of SUSY breaking terms as well as supersymmetric couplings. It is found that the magnitudes of SUSY breaking terms are suppressed in most regimes of the RG flow through the duality cascade. At one stage of cascading, the gaugino mass of the strongly coupled sector and scalar masses converge to certain values, which are determined by the gauge coupling and the gaugino mass of the weakly coupled sector. At the next stage, the strongly and weakly coupled sectors are interchanged with each other. We also show the possibility that cascading would be terminated by the gauge symmetry breaking, which is induced by the so-called $B$-term.

We investigate spherically symmetric nontopological solitons in electrodynamics with a scalar field self-interaction $U\sim |\psi |$ taken from the complex signum-Gordon model. We find $Q$-balls for small absolute values of the total electric charge $Q$, and $Q$-shells when $|Q|$ is large enough. In both cases the charge density exactly vanishes outside certain compact regions in the three-dimensional space. The dependence of the total energy $E$ of small $Q$-balls on the total electric charge has the form $E\sim |Q{|}^{5/6}$, while in the case of very large $Q$-shells, $E\sim |Q{|}^{7/6}$.

We present a series of supersymmetric models exhibiting an entirely new vacuum structure: towers of metastable vacua with higher and higher energies. As the number of vacua grows towards infinity, the energy of the highest vacuum remains fixed while the energy of the true ground state tends towards zero. We study the instanton-induced tunneling dynamics associated with such vacuum towers and find that many distinct decay patterns along the tower are possible: these include not only regions of vacua experiencing direct collapses and/or tumbling cascades, but also other regions of vacua whose stability is protected by “great walls” as well as regions of vacua populating “forbidden cities” into which tunneling cannot occur. We also discuss possible applications of this setup for the cosmological-constant problem, for studies of the string landscape, for supersymmetry breaking, and for $Z^{\prime }$ phenomenology. Finally, we point out that a limiting case of our setup yields theories with yet another new vacuum structure: infinite numbers of degenerate vacua. As a result, the true ground states of such theories are Bloch waves, with energy eigenvalues approximating a continuum and giving rise to a vacuum “band” structure.

Viable models of modified gravity which satisfy both local as well as cosmological tests are investigated. It is demonstrated that some versions of such highly nonlinear models exhibit multiple de Sitter universe solutions, which often appear in pairs, one of them being stable and the other unstable. It is explicitly shown that, for some values of the parameters, it is possible to find several de Sitter spaces (as a rule, numerically); one of them may serve for the inflationary stage, while the other can be used for the description of the dark energy epoch. The numerical evolution of the effective equation of state parameter is also presented, showing that these models can be considered as natural candidates for the unification of early-time inflation with late-time acceleration through de Sitter critical points. Moreover, based on the de Sitter solutions, multiple Schwarzschild-de Sitter universes are constructed which might also appear at the (pre-)inflationary stage. Their thermodynamics are studied and free energies are compared.

We introduce the Lagrangian for a multiscalar-field configuration in an $N$-dimensional internal space endowed with a constant metric $Q_{ik}$, and generalize the quintom cosmological scenario. We find the energy momentum tensor of the model and show that the set of dual transformations, which preserve the form of the Einstein equations in the Friedmann-Robertson-Walker cosmology, is enlarged. We show that the stability of the power-law solutions leads to an exponential potential which is invariant under linear transformations in the internal space. Moreover, we obtain the general exact solution of the Einstein-Klein-Gordon equations for that potential. There exist solutions that cross the phantom divide and solutions that blow up at a finite time, exhibiting a superaccelerated behavior and ending in a big rip. We show that the quintom model with a separable potential can be identified with a mixture of several fluids. This framework includes the $\Lambda \mathrm{CDM}$ model, a bouncing model, and a setting sourced by a cosmic string network plus a cosmological constant. Then we concentrate on the case where the dimension of the internal quintessence sector $N_q$ exceeds the dimension of the internal phantom sector $N_{\mathrm{ph}}$. For $(N_q,N_{\mathrm{ph}})=(2,1)$ the dark energy density derived from the 3-scalar field crosses the phantom divide, and its negative component plays the role of the negative part of a classical Dirac field.

The analysis of modern cosmological data is becoming an increasingly important task as the amount of data multiplies. An important goal is to extract geometric information, i.e. the metric of the cosmos, from observational data. The observer metric is adapted to the reality of observations: information received along the past null cone, and matter flowing along timelike lines. It provides a potentially very good candidate for developing a general numerical data reduction program. As a basis for this, we elucidate the spherically symmetric solution, for which there is to date no single presentation that is complete and correct. With future numerical implementation in mind, we give a clear presentation of the mathematical solution in terms of 4 arbitrary functions, the solution algorithm given observational data on the past null cone, and we argue that the evolution from one null cone to the next necessarily involves integrating down each null cone.

We have performed numerical simulations of SU(3) gauge theory coupled to $N_f=2$ flavors of symmetric-representation fermions. The fermions are discretized with the tadpole-improved clover action. Our simulations are done on lattices of length $L=6$, 8, and 12. In all simulation volumes we observe a crossover from a strongly coupled confined phase to a weak-coupling deconfined phase. Degeneracies in screening masses, plus the behavior of the pseudoscalar decay constant, indicate that the deconfined phase is also a phase in which chiral symmetry is restored. The movement of the confinement transition as the volume is changed is consistent with avoidance of the basin of attraction of an infrared fixed point of the massless theory.

We analyze the effects of charged lepton corrections and renormalization group (RG) running on the low energy predictions of theories which accurately predict tri-bimaximal neutrino mixing at the high energy scale. In particular we focus on grand unified theory (GUT) inspired seesaw models with accurate tri-bimaximal neutrino mixing at the GUT scale, in which the charged lepton corrections are Cabibbo-like and give rise to sum rules valid at the GUT scale. We study numerically the RG corrections to a variety of such neutrino mixing sum rules in order to assess their accuracy and reliability when comparing them to future low energy neutrino oscillation experiments. Our results indicate that the RG corrections to neutrino mixing sum rules are typically small (less than one degree), at least in the examples studied with hierarchical neutrinos.

We comment on a recent publication by Fosco, Lombardo, and Mazzitelli on Casimir energies for material slabs (“finite-width mirrors”) and report a discrepancy between results obtained there for a single mirror and some previous calculations. We provide a simple consistency check which proves that the method used by Fosco et al. is not reliable when applied to approximations of piecewise constant profile of the mirror. We also present an alternative method for calculation of the Casimir energy in such systems based on earlier work of ours. Our results coincide both with perturbation theory and with some older and more recent calculations, but differ from those of Fosco et al.

We extend our previous calculation of the quasilocal contribution to the self-force on a scalar particle to general (not necessarily geodesic) motion in a general spacetime. In addition to the general case and the case of a particle at rest in a stationary spacetime, we consider as examples a particle held at rest in Reissner-Nordström and Kerr-Newman spacetimes. This allows us to most easily analyze the effect of nongeodesic motion on our previous results and also allows for comparison to existing results for Schwarzschild spacetime.

An explicit and simple solution representing the wormhole formation is presented. The spacetime is constructed by gluing the Minkowski and Roberts spacetimes at null hypersurfaces in a regular manner. The parameters in the Roberts solution are required to give the negative kinetic term for the massless scalar field. Although a curvature singularity appears at the moment of the wormhole formation, it disappears instantaneously. This instantaneous singularity is weak in the senses of both Tipler and Królak along radial causal geodesics.

We analyze a simple extension of the standard model (SM) obtained by adding a complex singlet to the scalar sector (cxSM). We show that the cxSM can contain one or two viable cold dark matter candidates and analyze the conditions on the parameters of the scalar potential that yield the observed relic density. When the cxSM potential contains a global $U(1)$ symmetry that is both softly and spontaneously broken, it contains both a viable dark matter candidate and the ingredients necessary for a strong first order electroweak phase transition as needed for electroweak baryogenesis. We also study the implications of the model for discovery of a Higgs boson at the Large Hadron Collider.

We study radial excitations of pseudoscalar and vector $q\overline{q}$ mesons within a chiral approach. We derive a general form for a chiral Lagrangian describing processes involving excited pseudoscalar and vector mesons. The parameters of the chiral Lagrangian are fitted using data and previous calculations in the framework of the ${}^{3}P_0$ model. Finite-width effects are examined and predictions for mesons previously not discussed are given. Available experimental data is analyzed whenever possible. Possible hints for exotic mesons and open interpretation issues are discussed.

We study weak decays of the charm- and bottom-strange mesons $D_{s0}^{*}(2317)$, $D_{s1}(2460)$, $B_{s0}^{*}(5725)$ and $B_{s1}(5778)$ with $f_0(980)$ in the final state by assuming a hadronic molecule interpretation for their structures. Since in the proposed framework the initial and final states are occupied by hadronic molecules, the predictions for observables can provide a sensitive tool to further test the hadronic molecule structure in future experiments.

The question of whether neutrino masses are Dirac or Majorana is one of the most important, and most difficult, questions remaining in the neutrino sector. Searches for neutrinoless double $\beta$ decay may help to resolve this question, but are also sensitive to new, higher-dimension $\Delta L=2$ operators. In this paper we place two phenomenological constraints on these operators at dimension $d\le 11$. First, we require that the operators obey the quark flavor symmetries of the standard model, with any violation of the symmetries being due to Yukawa interactions, a scheme known as minimal flavor violation. Second, we require that the operators which generate neutrinoless double $\beta$ decay, and any operators related by the flavor symmetries, do not induce neutrino masses above the experimental and astrophysical limits. We find that these requirements severely constrain the operators which can violate lepton number, such that most can no longer contribute to neutrinoless double $\beta$ decay at observable rates. It is noteworthy that quark flavor symmetries can play such a strong role in constraining new leptonic physics, even when that physics is not quark flavor changing. Those few operators that can mimic a Majorana neutrino mass then appear with cutoffs below a TeV, and represent new physics which could be directly probed at the LHC or a future linear collider.

We show that at the level of linear response the low-frequency limit of a strongly coupled field theory at finite temperature is determined by the horizon geometry of its gravity dual, i.e., by the “membrane paradigm” fluid of classical black hole mechanics. Thus, generic boundary theory transport coefficients can be expressed in terms of geometric quantities evaluated at the horizon. When applied to the stress tensor this gives a simple, general proof of the universality of the shear viscosity in terms of the universality of gravitational couplings, and when applied to a conserved current it gives a new general formula for the conductivity. Away from the low-frequency limit the behavior of the boundary theory fluid is no longer fully captured by the horizon fluid even within the derivative expansion; instead, we find a nontrivial evolution from the horizon to the boundary. We derive flow equations governing this evolution and apply them to the simple examples of charge and momentum diffusion.

In quenched QCD, where the dynamic creation of quark-antiquark pairs out of the vacuum is neglected, a confined baryonic system composed of three static quarks exhibits stringlike behavior at large interquark separation, with the formation of flux tubes characterized by the geometry of the so-called $Y$ ansatz. We study the fluctuations of the junction of the three flux tubes, assuming the dynamics to be governed by an effective bosonic string model. We show that the asymptotic behavior of the effective width of the junction grows logarithmically with the distance between the sources, with the coefficient depending on the number of joining strings, on the dimension of spacetime and on the string tension.

The Hamiltonian of classical anti–de Sitter gravity is a pure boundary term on-shell. If this remains true in nonperturbative quantum gravity then (i) boundary observables will evolve unitarily in time and (ii) the algebra of boundary observables is the same at all times. In particular, information available at the boundary at any one time $t_1$ remains available at any other time $t_2$. Since there is also a sense in which the equations of motion propagate information into the bulk, these observations raise what may appear to be potential paradoxes concerning simultaneous (or spacelike separated) measurements of noncommuting observables, one at the asymptotic boundary and one in the interior. We argue that such potentially paradoxical settings always involve a breakdown of semiclassical gravity. In particular, we present evidence that making accurate holographic measurements over short time scales radically alters the familiar notion of causality. We also describe certain less intrinsically paradoxical settings which illustrate the above boundary unitarity and render the notion more concrete.