We study the low-temperature limit of warm inflation in a hilltop model. This limit remains valid up to the end of inflation, allowing an analytic description of the entire inflationary stage. In the weak dissipative regime, if the kinetic density of the inflaton dominates after inflation, low-scale inflation is attained with Hubble scale as low as 1 GeV. In the strong dissipative regime, the model satisfies the observational requirements for the spectral index with a mild tuning of the model parameters, while also overcoming the $\eta$-problem of inflation. However, there is some danger of gravitino overproduction unless the particle content of the theory is large.

In this paper we analyze the biasing effect of point sources, either thermal Sunyaev-Zeldovich clusters or standard radio sources, on the estimated strength of the non-Gaussianity in the cosmic microwave background (CMB). We show that the biggest contribution comes from the cross correlation of the CMB with the matter density rather than from the Poisson term which is conventionally assumed in these calculations. For the three year WMAP data, we estimate that point sources could produce a non-Gaussian signature equivalent to a bias in $f_{NL}$ of 0.35, 0.24, $-0.097$, $-0.13$ in the Ka, Q, V, and W bands, respectively. The level of bias we find is largely insufficient to explain the very high $f_{NL}$ values recently detected by Yadav and Wandelt. For Planck, we estimate the point source bispectra to contaminate the $f_{NL}$ estimator with a bias of 1.3, 0.34, $-0.25$, $-0.48$ at 30, 44, 70, 100 GHz, respectively. These results depend on the assumed redshift distribution of the point sources. However, given the projected Planck sensitivity of $\Delta f_{NL}\simeq 5$ (95% C.L.), a good estimate of point sources’ properties including their number density and redshift distribution is essential before deriving strong conclusions on primordial non-Gaussianity.

In this paper, we present a successful implementation of a subtraction-noise projection method into a simple, simulated data analysis pipeline of a gravitational-wave search. We investigate the problem to reveal a weak stochastic background signal which is covered by a strong foreground of compact-binary coalescences. The foreground, which is estimated by matched filters, has to be subtracted from the data. Even an optimal analysis of foreground signals will leave subtraction noise due to estimation errors of template parameters which may corrupt the measurement of the background signal. The subtraction noise can be removed by a noise projection. We apply our analysis pipeline to the proposed future-generation space-borne Big Bang Observer mission which seeks for a stochastic background of primordial gravitational waves in the frequency range $\sim 0.1\mathrm{Hz}—1\mathrm{Hz}$ covered by a foreground of black-hole and neutron-star binaries. Our analysis is based on a simulation code which provides a dynamical model of a time-delay interferometer network. It generates the data as time series and incorporates the analysis pipeline together with the noise projection. Our results confirm previous ad hoc predictions which say that the Big Bang Observer will be sensitive to backgrounds with fractional energy densities below $\Omega ={10}^{-16}$.

We propose a three-dimensional electromagnetic current operator within light-front dynamics that satisfies a light-front Ward-Takahashi identity for two-fermion systems. The light-front current operator is obtained by a quasipotential reduction of the four-dimensional current operator and acts on the light-front valence component of bound or scattering states. A relation between the light-front valence wave function and the four-dimensional Bethe-Salpeter amplitude both for bound or scattering states is also derived, such that the matrix elements of the four-dimensional current operator can be fully recovered from the corresponding light-front ones. The light-front current operator can be perturbatively calculated through a quasipotential expansion, and the divergence of the proposed current satisfies a Ward-Takahashi identity at any given order of the expansion. In the quasipotential expansion the instantaneous terms of the fermion propagator are accounted for by the effective interaction and two-body currents. We exemplify our theoretical construction in the Yukawa model in the ladder approximation, investigating in detail the current operator at the lowest nontrivial order of the quasipotential expansion of the Bethe-Salpeter equation. The explicit realization of the light-front form of the Ward-Takahashi identity is verified. We also show the relevance of instantaneous terms and of the pair contribution to the two-body current and the Ward-Takahashi identity.

We report on a relation between the decay constants of $\rho$-like $J^{PC}=1^{--}$ vector mesons, which arises solely from the perturbative analysis of the $⟨VV⟩$, $⟨TT⟩$ and $⟨VT⟩$ correlators at $\mathcal{O}({\alpha }_s^0)$ in the large-$N_c$ limit. We find $f_V^T/f_V=1/\sqrt{2}$ for highly excited states together with a pattern of alternation in sign. Quite remarkably, recent lattice determinations reported $f_{\rho }^T(\mu )/f_{\rho }=0.72(2)$ at $\mu =2\mathrm{GeV}$, in excellent agreement with our large-$N_c$ result. This seems to suggest a pattern like $f_{Vn}^T/f_{Vn}=(-1{)}^n/\sqrt{2}$ for the whole ($1^{--}$) states. In order to test this conjecture in real QCD we construct a set of spectral sum rules, which turn out to comply nicely with this scenario.

The measurement of $B^{\pm }\to {\tau }^{\pm }{\nu }_{\tau }$ at the $B$ factories provides important constraints on the parameter $\tan \beta /m_{H^{\pm }}$ in the context of models with two Higgs doublets. Limits on this decay from $e^{+}{e}^{-}$ collisions at the $Z$ peak were sensitive to the sum of $B^{\pm }\to {\tau }^{\pm }{\nu }_{\tau }$ and $B_c^{\pm }\to {\tau }^{\pm }{\nu }_{\tau }$. Because of the possibly sizeable contribution from $B_c^{\pm }\to {\tau }^{\pm }{\nu }_{\tau }$ we suggest that a signal for this combination might be observed if the CERN LEP L3 Collaboration used its total data of $\sim 3.6\times {10}^6$ hadronic decays of the $Z$ boson. Moreover, we point out that a future linear collider operating at the $Z$ peak (Giga $Z$ option) could constrain $\tan \beta /m_{H^{\pm }}$ from the sum of these processes with a precision comparable to that anticipated at proposed high luminosity $B$ factories from $B^{\pm }\to {\tau }^{\pm }{\nu }_{\tau }$ alone.

Anomaly mediated supersymmetry breaking, when implemented in the minimal supersymmetric standard model, is known to suffer from the problem of negative slepton mass squared leading to the breakdown of electric charge conservation. We show, however, that when the minimal supersymmetric standard model is extended to explain small neutrino masses by including a pair of superheavy Higgs triplet superfields (the type II seesaw mechanism), the slepton masses can be deflected from the pure anomaly mediated supersymmetry breaking trajectory and become positive. In the simple model we present in this paper, the seesaw scale is about ${10}^{13}–{10}^{14}\mathrm{GeV}$. Gauge coupling unification can be maintained by embedding the triplet to $SU(5)$ $\mathbf{15}$-multiplet. In this scenario, the $b$-ino is the lightest supersymmetric particle and its mass is nearly degenerate with the next-to-lightest supersymmetric particle slepton when the triplet mass is right around the seesaw scale.

At the quark level there are basically two types of contributions of $R$-parity violating supersymmetry (${\mathrm{R̸}}_p$ SUSY) to neutrinoless double beta decay: the short-range contribution involving only heavy virtual superpartners and the long-range one with the virtual squark and neutrino. Hadronization of the effective operators, corresponding to these two types of contributions, may in general involve virtual pions in addition to close on-mass-shell nucleons. From the previous studies it is known that the short-range contribution is dominated by the pion exchange. In the present paper we show that this is also true for the long-range ${\mathrm{R̸}}_p$ SUSY contribution. Therefore, we conclude that the ${\mathrm{R̸}}_p$ SUSY contributes to the neutrinoless double beta decay dominantly via charged pion exchange between the decaying nucleons.

Two recent papers reconsider the possibility that the WMAP haze is due to the synchrotron emission originated by neutralino self-annihilation; also upper bounds on the neutralino self-annihilation cross section are suggested. We show that for thermal weakly interacting massive particles (WIMPs) in a standard cosmological model, when the galactic WIMP density is duly rescaled for subdominant WIMPs, the upper bound applicable generically to any signal due to self-conjugate WIMPs is more stringent than the ones obtained from analysis of the WMAP haze. We also argue that an experimental upper bound, which can compete with our generic upper limit, can rather be derived from measurements of cosmic antiproton fluxes. Finally, we comment on the possible impact of our generic upper bound on the interpretation of the WMAP haze in terms of thermal neutralinos in a standard cosmological scheme.

In the framework of boundary conformal field theory we consider a flat unstable $\mathrm{D}p$-brane in the presence of a large constant electromagnetic field. Specifically, we study the case that the electromagnetic field satisfy the following three conditions: (i) a constant electric field is turned on along the $x^1$ direction ($E_1\ne 0$); (ii) the determinant of the matrix ($\eta +F$) is negative so that it lies in the physical region ($-\det (\eta +F)>0$); (iii) the 11-component of its cofactor is positive to the large electromagnetic field. In this case, we identify exactly marginal deformations depending on the spatial coordinate $x^1$. They correspond to tachyon profiles of hyperbolic sine, exponential, and hyperbolic cosine types. Boundary states are constructed for these deformations by utilizing $T$-duality approach and also by directly solving the overlap conditions in BCFT. The exponential type deformation gives a tensionless half brane connecting the perturbative string vacuum and one of the true tachyon vacua, while the others have negative tensions. This is in agreement with the results obtained in other approaches.

We clarify the relation between the vertex operators in type IIB matrix model and superstring. Green-Schwarz light-cone closed superstring theory is obtained from IIB matrix model on two-dimensional noncommutative backgrounds. Superstring vertex operators should be reproduced from those of IIB matrix model through this connection. Indeed, we confirm that supergravity vertex operators in IIB matrix model on the two-dimensional backgrounds reduce to those in superstring theory. Noncommutativity plays an important role in our identification. Through this correspondence, we can reproduce superstring scattering amplitudes from IIB matrix model.

We investigate the relationship between a gauge theory on a principal bundle and that on its base space. In the case where the principal bundle is itself a group manifold, we also study relations of those gauge theories with a matrix model obtained by dimensionally reducing them to zero dimensions. First, we develop the dimensional reduction of Yang-Mills (YM) theory on the total space to YM-Higgs theory on the base space for a general principal bundle. Second, we show a relationship that YM on an $SU(2)$ bundle is equivalent to the theory around a certain background of YM-Higgs on its base space. This is an extension of our previous work [T. Ishii, G. Ishiki, S. Shimasaki, and A. Tsuchiya, J. High Energy Phys. 05 (2007) 014.], in which the same relationship concerning a $U(1)$ bundle is shown. We apply these results to the case of $SU(n+1)$ as the total space. By dimensionally reducing YM on $SU(n+1)$, we obtain YM-Higgs on $SU(n+1)/SU(n)\simeq S^{2n+1}$ and on $SU(n+1)/(SU(n)\times U(1))\simeq C{P}^n$ and a matrix model. We show that the theory around each monopole vacuum of YM-Higgs on $C{P}^n$ is equivalent to the theory around a certain vacuum of the matrix model in the commutative limit. By combining this with the relationship concerning a $U(1)$ bundle, we realize YM-Higgs on $SU(n+1)/SU(n)\simeq S^{2n+1}$ in the matrix model. We see that the relationship concerning a $U(1)$ bundle can be interpreted as Buscher’s T-duality.

We study the possible phenomenology of a three-family Pati-Salam model constructed from intersecting D6-branes in type IIA string theory on the ${\mathbf{T}}^{\mathbf{6}}/({\mathbb{Z}}_{\mathbf{2}}\times {\mathbb{Z}}_{\mathbf{2}})$ orientifold with some desirable semirealistic features. In the model, tree-level gauge-coupling unification is achieved automatically at the string scale, and the gauge symmetry may be broken to the standard model (SM) close to the string scale. The small number of extra chiral exotic states in the model may be decoupled via the Higgs mechanism and strong dynamics. We calculate the possible supersymmetry breaking soft terms and the corresponding low-energy supersymmetric particle spectra which may potentially be tested at the Large Hadron Collider (LHC). We find that for the viable regions of the parameter space the lightest $CP$-even Higgs boson mass usually satisfies $m_H\le 120\mathrm{GeV}$, and the observed dark matter density may be generated. Finally, we find that it is possible to obtain correct SM quark masses and mixings, and the tau lepton mass at the unification scale. Additionally, neutrino masses and mixings may be generated via the seesaw mechanism. Mechanisms to stabilize the open and closed-string moduli, which are necessary for the model to be truly viable and to make definite predictions are discussed.

We demonstrate how to obtain from the Schwinger-Dyson equations of QCD an infrared finite ghost propagator in the Feynman gauge. The key ingredient in this construction is the longitudinal form factor of the nonperturbative gluon-ghost vertex, which, contrary to what happens in the Landau gauge, contributes nontrivially to the gap equation of the ghost. The detailed study of the corresponding vertex equation reveals that in the presence of a dynamical infrared cutoff this form factor remains finite in the limit of vanishing ghost momentum. This, in turn, allows the ghost self-energy to reach a finite value in the infrared, without having to assume any additional properties for the gluon-ghost vertex, such as the presence of massless poles. The implications of this result and possible future directions are briefly outlined.

Many of the most important astrophysical tests of Lorentz symmetry also assume that energy momentum of the observed particles is exactly conserved. In the causal set approach to quantum gravity a particular kind of Lorentz symmetry holds but energy-momentum conservation may be violated. We show that incorrectly assuming exact conservation can give rise to a spurious signal of Lorentz symmetry violation for a causal set. However, the size of this spurious signal is much smaller than can be currently detected and hence astrophysical Lorentz symmetry tests as currently performed are safe from causal set induced violations of energy-momentum conservation.

The spinless Bañados-Teiltelboim-Zanelli spacetime is considered in the quantum theory context. Specifically, we study the case of a negative mass parameter using quantum test particles obeying the Klein-Gordon and Dirac equations. We study if this classical singular spacetime, with a naked singularity at the origin, remains singular when tested with quantum particles. The need for additional information near the origin is confirmed for massive scalar particles and all of the possible boundary conditions necessary to turn the spatial portion of the wave operator self-adjoint are found. When tested by massless scalar particles or fermions, the singularity is “healed” and no extra boundary condition is needed. Near infinity, no boundary conditions are necessary.

In the context of quantum gravity phenomenology, we study the Unruh effect in the presence of superluminal dispersion relations. In particular, we estimate the response function and the probability rate for an accelerated detector coupled to a massless scalar field, whose dispersion relation becomes essentially quadratic beyond a threshold momentum $k_p$. By means of a perturbative analysis, we show that superluminal dispersion induces a correction to the Planckian spectrum, which tends to vanish as $k_p$ increases.

Detailed physical processes of magnetic field generation from density fluctuations in the prerecombination era are studied. Solving Maxwell equations and the generalized Ohm’s law, the evolutions of the net charge density, the electric current, and the electromagnetic field are solved. Unlike most of the previous works, we treat electrons and photons as separate components under the assumption of tight coupling. We find that generation of the magnetic field due to density fluctuations takes place only from the second order of both perturbation theory and the tight coupling approximation.

A model of nonlocal dilaton interactions, motivated by string duality symmetries, is applied to a scenario of “coupled quintessence” in which the dilaton dark energy is nonlocally coupled to the dark-matter sources. It is shown that the nonlocal effects tend to generate a backreaction which—for strong enough coupling—can automatically compensate the acceleration due to the negative pressure of the dilaton potential, thus asymptotically restoring the standard (dust-dominated) decelerated regime. This result is illustrated by analytical computations and numerical examples.

The observed velocities of pulsars suggest the possibility that sterile neutrinos with mass of several keV are emitted from a cooling neutron star. The same sterile neutrinos could constitute all or part of cosmological dark matter. The neutrino-driven kicks can exhibit delays depending on the mass and the mixing angle, which can be compared with the pulsar data. We discuss the allowed ranges of sterile neutrino parameters, consistent with the latest cosmological and x-ray bounds, which can explain the pulsar kicks for different delay times.