We show that the causal-set approach to creating an ever-present cosmological “constant” in the expanding universe is strongly constrained by the isotropy of the microwave background. Fluctuations generated by stochastic lambda generation which are consistent with COBE and WMAP observations are far too small to dominate the expansion dynamics at $z<1000$ and so cannot explain the observed late-time acceleration of the universe. We also discuss other observational constraints from the power spectrum of galaxy clustering and show that the theoretical possibility of ever-present lambda arises only in $3+1$ dimensional space-times.

We introduce three space-times that are discrete in time and compatible with the Lorentz symmetry. We show that these spaces are not commutative, with commutation relations similar to the relations of the Snyder and Yang spaces. Furthermore, using a reparametrized relativistic particle we obtain a realization of the Snyder type spaces and we construct an action for them.

It is shown that the anomaly inflow mechanism can be implemented using Wilson lines in odd dimensional gauge theories. An action of Wess-Zumino-Witten type can be constructed using Wilson lines. The action is understood in the odd dimensional bulk space-time rather than in the even dimensional boundary. This action is not gauge invariant. It gives anomalous gauge variations of the consistent form on boundary space-times. So it can be used to cancel the quantum anomalies localized on boundary space-times. This offers a new way to cancel the gauge anomaly and construct anomaly-free gauge theory in odd dimensional space-time.

We study the effect of cosmological expansion on orbits—galactic, planetary, or atomic—subject to an inverse-square force law. We obtain the laws of motion for gravitational or electrical interactions from general relativity—in particular, we find the gravitational field of a mass distribution in an expanding universe by applying perturbation theory to the Robertson-Walker metric. Cosmological expansion induces an ($\ddot{a}/a)\overrightarrow{r}$ force where $a(t)$ is the cosmological scale factor. In a locally Newtonian framework, we show that the $(\ddot{a}/a)\overrightarrow{r}$ term represents the effect of a continuous distribution of cosmological material in Hubble flow, and that the total force on an object, due to the cosmological material plus the matter perturbation, can be represented as the negative gradient of a gravitational potential whose source is the material actually present. We also consider the effect on local dynamics of the cosmological constant. We calculate the perihelion precession of elliptical orbits due to the cosmological constant induced force, and work out generalizations to the rotation curve and virial relation applicable to clusters of galaxies.

A brane scenario is envisaged in which the $m$-dimensional bulk is endowed with a Gauss-Bonnet term and localization of matter on the brane is achieved by means of a confining potential. The resulting Friedmann equations on the brane are modified by various extra terms that may be interpreted as the X-matter, providing a possible phenomenological explanation for the accelerated expansion of the Universe. The age of the Universe in this scenario is studied and shown to be consistent with the present observational data.

We propose a modified version of the Horowitz-Maldacena final-state boundary condition based upon a matter-radiation thermalization hypothesis on the Black Hole interior, which translates into a particular entangled state with thermal Schmidt coefficients. We investigate the consequences of this proposal for matter entering the horizon, as described by a Canonical density matrix characterized by the matter temperature $T$. The emitted radiation is explicitly calculated and is shown to follow a thermal spectrum with an effective temperature $T_{\mathrm{eff}}$. We analyze the evaporation process in the quasistatic approximation, highlighting important differences in the late stages with respect to the usual semiclassical evolution, and calculate the fidelity of the emitted Hawking radiation relative to the infalling matter.

In this paper we revisit the relation between the Friedmann equations and the first law of thermodynamics. We find that the unified first law first proposed by Hayward to treat the outertrapping horizon of a dynamical black hole can be used to the apparent horizon (a kind of inner trapping horizon in the context of the FRW cosmology) of the FRW universe. We discuss three kinds of gravity theorties: Einstein theory, Lovelock thoery, and scalar-tensor theory. In Einstein theory, the first law of thermodynamics is always satisfied on the apparent horizon. In Lovelock theory, treating the higher derivative terms as an effective energy-momentum tensor, we find that this method can give the same entropy formula for the apparent horizon as that of black hole horizon. This implies that the Clausius relation holds for the Lovelock theory. In scalar-tensor gravity, we find, by using the same procedure, the Clausius relation no longer holds. This indicates that the apparent horizon of the FRW universe in the scalar-tensor gravity corresponds to a system of nonequilibrium thermodynamics. We show this point by using the method developed recently by Eling et al. for dealing with the $f(R)$ gravity.

The cosmological constant and many other possible origins for acceleration of the cosmic expansion possess variations in the dark energy properties slow on the Hubble time scale. Given that models with more rapid variation, or even phase transitions, are possible though, we examine the fineness in redshift with which cosmological probes can realistically be employed, and what constraints this could impose on dark energy behavior. In particular, we discuss various aspects of baryon acoustic oscillations, and their use to measure the Hubble parameter $H(z)$. We find that currently considered cosmological probes have an innate resolution no finer than $\Delta z\approx 0.2–0.3$.

We compute the one-loop correction to the radion potential in the Randall-Sundrum model with detuned brane tensions, with supersymmetry broken by boundary conditions. We concentrate on the small warping limit, where the one-loop correction is significant. With pure supergravity, the correction is negative, but with bulk hypermultiplets, the correction can be positive, so that the 4d curvature can be lowered, with the radion stable. We use both the KK theory, and the 4d radion effective theory for this study.

The recent WMAP data have confirmed that exotic dark matter together with the vacuum energy (cosmological constant) dominate in the flat Universe. Thus the direct dark matter search, consisting of detecting the recoiling nucleus, is central to particle physics and cosmology. Modern particle theories naturally provide viable cold dark matter candidates with masses in the GeV-TeV region. Supersymmetry provides the lightest supersymmetric particle (LSP), theories in extra dimensions the lightest Kaluza-Klein particle (LKP) etc. Unfortunately, however, in nuclear recoil measurements the interesting signal cannot be easily distinguished from the background. So, to minimize the background problems, one should exploit characteristic signatures of the reaction, such as the modulation effect and, in directional experiments, the correlation of the event rates with the sun’s motion. In standard nondirectional experiments the modulation is small, less than two per cent and the location of the maximum depends on the unknown particle’s mass. In directional experiments, in addition to the forward-backward asymmetry due to the sun’s motion, one expects a larger modulation, which depends on the direction of observation. We study such effects both in the case of a light and a heavy target. Furthermore, since it now appears that the planned experiments may be only partly directional, in the sense that they can only detect the line of the recoiling nucleus, but not the sense of direction on it, we study which of the above mentioned interesting features, if any, will persist in these less ambitious experiments.

We study the littlest Higgs model with $T$ parity at the CERN LHC through pair productions of the $T$-odd top quark partner ($T_{-}$) which decays into the top quark and the lightest $T$-odd particle. We identify the region of parameters favored by the electroweak and cosmological considerations. The signal and background events are simulated with fast detector simulation to study the discovery potential at the LHC. We find that the hemisphere analysis recently proposed by the CMS Collaboration is very useful to separate the signal from the $t\overline{t}$ background. We discuss the observability of the top tagged signal in the effective mass ($M_{\mathrm{eff}}$) versus the transverse missing energy ($E_{\mathrm{Tmiss}}$) plane. We show that, for all our sample parameter sets with $M_{T_{-}}\le 900\mathrm{GeV}$, the excess of the signal over the background can be visible as a bump structure in the $E_{\mathrm{Tmiss}}$ distribution for $50{\mathrm{fb}}^{-1}$ at relatively high $M_{\mathrm{eff}}$ intervals.

We consider two-level detectors coupled to a scalar field and moving on arbitrary trajectories in Minkowski space-time. We first derive a generic expression for the response function using a (novel) regularization procedure based on the Feynman prescription that is explicitly causal, and we compare it to other expressions used in the literature. We then use this expression to study, analytically and numerically, the time dependence of the response function in various nonstationarity situations. We show that, generically, the response function decreases like a power in the detector’s level spacing, $E$, for high $E$. It is only for stationary worldlines that the response function decays faster than any power law, in keeping with the known exponential behavior for some stationary cases. Under some conditions the (time-dependent) response function for a nonstationary worldline is well approximated by the value of the response function for a stationary worldline having the same instantaneous acceleration, torsion, and hypertorsion. While we cannot offer general conditions for this to apply, we discuss special cases; in particular, the low-energy limit for linear space trajectories.

We consider intersecting $D$-brane models which have two dimensional chiral fermions localized at the intersections. At weak coupling, the interactions of these fermions are described by generalized Gross-Neveu models. At strong coupling, these configurations are described by the dynamics of probe $D$-branes in a curved background spacetime. We study patterns of dynamical chiral symmetry breaking in these models at weak and strong coupling, and also discuss relationships between these two descriptions.

It is proven that in Vaidya spacetimes of bounded total mass, the outer boundary, in spacetime, of the region containing outer trapped surfaces, is the event horizon. Further, it is shown that the region containing trapped surfaces in these spacetimes does not always extend to the event horizon.

I evaluate the largest three-loop corrections to the mass of the lightest Higgs scalar boson in the minimal supersymmetric standard model in a mass-independent renormalization scheme, using effective field theory and renormalization group methods. The contributions found here are those that depend only on strong and Yukawa interactions and on the leading and next-to-leading logarithms of the ratio of a typical superpartner mass scale to the top-quark mass. The approximation assumes that all superpartners and the other Higgs bosons can be treated as much heavier than the top quark, but does not assume their degeneracy. I also discuss the consistent addition of the three-loop corrections to a complete two-loop calculation.

We study rapidity gap survival (RGS) in the production of high-mass systems ($H=\mathrm{\text{dijet}}$, heavy quarkonium, Higgs boson) in double-gap exclusive diffractive $pp$ scattering, $pp\to p+(\mathrm{\text{gap}})+H+(\mathrm{\text{gap}})+p$. Our approach is based on the idea that hard and soft interactions are approximately independent because they proceed over widely different time and distance scales. We implement this idea in a partonic description of proton structure, which allows for a model-independent treatment of the interplay of hard and soft interactions. The high-mass system is produced in a hard scattering process with exchange of two gluons between the protons, whose amplitude is calculable in terms of the gluon generalized parton distribution (GPD), measured in exclusive $ep$ scattering. The hard scattering process is modified by soft spectator interactions, which we calculate neglecting correlations between hard and soft interactions (independent interaction approximation). We obtain an analytic expression for the RGS probability in terms of the phenomenological $pp$ elastic scattering amplitude, without reference to the eikonal approximation. Contributions from inelastic intermediate states are suppressed. The onset of the black-disk limit in $pp$ scattering at TeV energies strongly suppresses diffraction at small impact parameters and is the main factor in determining the RGS probability. Correlations between hard and soft interactions (e.g. due to scattering from the long-range pion field of the proton or due to possible short-range transverse correlations between partons) further decrease the RGS probability. We also investigate the dependence of the diffractive cross section on the transverse momenta of the final-state protons (“diffraction pattern”). By measuring this dependence one can perform detailed tests of the interplay of hard and soft interactions and even extract information about the gluon GPD in the proton. Such studies appear to be feasible with the planned forward detectors at the Large Hadron Collider.

If the dark matter of the Universe is made of sterile neutrinos with mass in the keV region, it can be searched for with the help of x-ray satellites. We discuss the prospects of laboratory experiments that can be competitive and complementary to space missions. We argue that the detailed study of $\beta$ decays of tritium and other nuclei with the help of cold target recoil ion momentum spectroscopy can potentially enter into an interesting parameter range and even supersede the current astronomical bounds on the properties of the dark matter sterile neutrinos.

We study a method to solve stationary axisymmetric vacuum Einstein equations numerically. As an illustration, the five-dimensional doubly spinning black rings that have two independent angular momenta are formulated in a way suitable for a fully nonlinear numerical method. Expanding for small second angular velocity, the formulation is solved perturbatively up to second order involving the backreaction from the second spin. The obtained solutions are regular without conical singularity, and the physical properties are discussed with the phase diagram of the reduced entropy vs the reduced angular momenta. Possible extensions of the present approach to constructing the higher-dimensional version of black ring and the ring with the cosmological constant are discussed also.

We show that reheating of the universe occurs spontaneously in a broad class of inflation models with $f(\varphi )R$ gravity ($\varphi$ is the inflaton). The model does not require explicit couplings between $\varphi$ and bosonic or fermionic matter fields. The couplings arise spontaneously when $\varphi$ settles in the vacuum expectation value (vev) and oscillates, with coupling constants given by derivatives of $f(\varphi )$ at the vev and the mass of resulting bosonic or fermionic fields. This mechanism allows inflaton quanta to decay into any fields which are not conformally invariant in $f(\varphi )R$ gravity theories.