By combining the numerical solution of the nonlinear hydrodynamics equations with the solution of the linear inhomogeneous Zerilli-Moncrief and Regge-Wheeler equations, we investigate the properties of the gravitational radiation emitted during the axisymmetric accretion of matter onto a Schwarzschild black hole. The matter models considered include quadrupolar dust shells and thick accretion disks, permitting us to simulate situations which may be encountered at the end stages of stellar gravitational collapse or binary neutron star merger. We focus on the interference pattern appearing in the energy spectra of the emitted gravitational waves and on the amount of excitation of the quasinormal modes of the accreting black hole. We show that, quite generically in the presence of accretion, the black-hole ringdown is not a simple superposition of quasinormal modes, although the fundamental mode is usually present and often dominates the gravitational-wave signal. We interpret this as due to backscattering of waves off the nonexponentially decaying part of the black-hole potential and to the finite spatial extension of the accreting matter. Our results suggest that the black-hole QNM contributions to the full gravitational-wave signal should be extremely small and possibly not detectable in generic astrophysical scenarios involving the accretion of extended distributions of matter.

I compute a renormalization group (RG) improvement to the standard beyond-linear-order Eulerian perturbation theory (PT) calculation of the power spectrum of large-scale density fluctuations in the Universe. At $z=0$, for a power spectrum matching current observations, lowest order RGPT appears to be as accurate as one can test using existing numerical simulation-calibrated fitting formulas out to at least $k\simeq 0.3h{\mathrm{Mpc}}^{-1}$; although inaccuracy is guaranteed at some level by approximations in the calculation (which can be improved in the future). In contrast, standard PT breaks down virtually as soon as beyond-linear corrections become non-negligible, on scales even larger than $k=0.1h{\mathrm{Mpc}}^{-1}$. This extension in range of validity could substantially enhance the usefulness of PT for interpreting baryonic acoustic oscillation surveys aimed at probing dark energy, for example. I show that the predicted power spectrum converges at high $k$ to a power law with index given by the fixed-point solution of the RG equation. I discuss many possible future directions for this line of work. The basic calculation of this paper should be easily understandable without any prior knowledge of RG methods, while a rich background of mathematical physics literature exists for the interested reader.

We derive constraints on a simple quintessential inflation model, based on a spontaneously broken ${\Phi }^4$ theory, imposed by the Wilkinson Microwave Anisotropy Probe three-year data (WMAP3) and by galaxy clustering results from the Sloan Digital Sky Survey (SDSS). We find that the scale of symmetry breaking must be larger than about 3 Planck masses in order for inflation to generate acceptable values of the scalar spectral index and of the tensor-to-scalar ratio. We also show that the resulting quintessence equation of state can evolve rapidly at recent times and hence can potentially be distinguished from a simple cosmological constant in this parameter regime.

There are compelling reasons to think that new physics will appear at or below the TeV scale. It is not known what form this new physics will take, however. Although The Large Hadron collider is very likely to discover new particles associated with the TeV scale, it may be difficult for it to determine the nature of those particles, whether superpartners, Kaluza-Klein modes or other states. In this article, we consider how direct and indirect dark matter detection experiments may provide information complementary to hadron colliders, which can be used to discriminate between supersymmetry, models with universal extra dimensions, and Little Higgs theories. We find that, in many scenarios, dark matter experiments can be effectively used to distinguish between these possibilities.

We use the scale of neutrino mass and naturalness considerations to obtain model-independent expectations for the magnitude of possible contributions to muon decay Michel parameters from new physics above the electroweak symmetry-breaking scale. Focusing on Dirac neutrinos, we obtain a complete basis of dimension four and dimension six effective operators that are invariant under the gauge symmetry of the standard model and that contribute to both muon decay and neutrino mass. We show that—in the absence of fine tuning—the most stringent neutrino-mass naturalness bounds on chirality-changing vector operators relevant to muon decay arise from one-loop operator mixing. The bounds we obtain on their contributions to the Michel parameters are 2 orders of magnitude stronger than bounds previously obtained in the literature. In addition, we analyze the implications of one-loop matching considerations and find that the expectations for the size of various scalar and tensor contributions to the Michel parameters are considerably smaller than derived from previous estimates of two-loop operator mixing. We also show, however, that there exist gauge-invariant operators that generate scalar and tensor contributions to muon decay but whose flavor structure allows them to evade neutrino-mass naturalness bounds. We discuss the implications of our analysis for the interpretation of muon-decay experiments.

We construct the Zinn-Justin-Batalin-Vilkovisky action for tachyons and gauge bosons from Witten’s 3-string vertex of the bosonic open string without gauge fixing. Through canonical transformations, we find the off-shell, local, gauge-covariant action up to 3-point terms, satisfying the usual field theory gauge transformations. Perturbatively, it can be extended to higher-point terms. It also gives a new gauge condition in field theory which corresponds to the Feynman-Siegel gauge on the world-sheet.

The universality of semiclassical gravity is investigated by considering the behavior of the quantities $⟨{\varphi }^2⟩$ and $⟨T^a{}_b⟩$, along with quantum corrections to the effective Newtonian potential in the far field limits of static spherically symmetric objects ranging from stars in the weak field Newtonian limit to black holes. For scalar fields it is shown that when differences occur they all result from the behavior of a single mode with zero frequency and angular momentum and are thus due to a combination of infrared and $s$-wave effects. An intriguing combination of similarities and differences between the extreme cases of a Schwarzschild black hole and a star in the weak field Newtonian limit is explained.

We examine the current directions in the search for spin-dependent dark matter. We discover that, with few exceptions, the search activity is concentrated towards constraints on the WIMP-neutron spin coupling, with significantly less impact in the WIMP-proton sector. We review the situation of those experiments with WIMP-proton spin sensitivity, toward identifying those capable of reestablishing the balance.

Inspirals of stellar-mass compact objects (COs) into $\sim {10}^6{M}_{\odot }$ black holes are especially interesting sources of gravitational waves for the planned Laser Interferometer Space Antenna (LISA). The orbits of these extreme-mass-ratio inspirals (EMRIs) are highly relativistic, displaying extreme versions of both perihelion precession and Lense-Thirring precession of the orbital plane. We investigate the question of whether the emitted waveforms can be used to strongly constrain the geometry of the central massive object, and in essence check that it corresponds to a Kerr black hole (BH). For a Kerr BH, all multipole moments of the spacetime have a simple, unique relation to $M$ and $S$, the BH mass, and spin; in particular, the spacetime’s mass quadrupole moment $Q$ is given by $Q=-S^2/M$. Here we treat $Q$ as an additional parameter, independent of $S$ and $M$, and ask how well observation can constrain its difference from the Kerr value. This was already estimated by Ryan, but for the simplified case of circular, equatorial orbits, and Ryan also neglected the signal modulations arising from the motion of the LISA satellites. We consider generic orbits and include the modulations due to the satellite motions. For this analysis, we use a family of approximate (basically post-Newtonian) waveforms, which represent the full parameter space of EMRI sources, and which exhibit the main qualitative features of true, general relativistic waveforms. We extend this parameter space to include (in an approximate manner) an arbitrary value of $Q$, and then construct the Fisher information matrix for the extended parameter space. By inverting the Fisher matrix, we estimate how accurately $Q$ could be extracted from LISA observations of EMRIs. For 1 yr of coherent data from the inspiral of a $10M_{\odot }$ black hole into rotating black holes of masses ${10}^{5.5}{M}_{\odot }$, ${10}^6{M}_{\odot }$, or ${10}^{6.5}{M}_{\odot }$, we find $\Delta (Q/M^3)\sim {10}^{-4}$, ${10}^{-3}$, or ${10}^{-2}$, respectively (assuming total signal-to-noise ratio of 100, typical of the brightest detectable EMRIs). These results depend only weakly on the eccentricity of the inspiral orbit or the spin of the central object.

We present a supersymmetric realization of the twin Higgs mechanism, which cancels off all contributions to the Higgs mass generated above a scale $f$. Radiative corrections induced by the top-quark sector lead to a breaking of the twin sector electroweak symmetry at a scale $f\sim \mathrm{TeV}$. In our sector, below the scale $f$, these radiative corrections from the top quark are present but greatly weakened, naturally allowing a $Z$ boson mass an order of magnitude below $f$, even with a top squark mass of order 1 TeV and a messenger scale near the Planck mass. A sufficient quartic interaction for our Higgs boson arises from the usual gauge contribution together with a radiative contribution from a heavy top squark. The mechanism requires the presence of an $SU(2)$-adjoint superfield, and can be simply unified. Naturalness in these theories is usually associated with light winos and sleptons, and is largely independent of the scale of the colored particles. The assumption of unification naturally predicts the existence of many exotic fields. The theory often has particles which may be stable on collider time scales, including an additional color octet superfield. In the limit that $m_{\mathrm{SUSY}}\gg f$, the mechanism yields a UV completion of the nonsupersymmetric twin Higgs, with the notable improvement of a tree-level quartic for the standard model Higgs. In this framework, a successful UV completion requires the existence of new charged fields well below the scale $f$.

We investigate the lattice QCD Dirac operator with staggered fermions at temperatures around the chiral phase transition. We present evidence of a metal-insulator transition in the low lying modes of the Dirac operator around the same temperature as the chiral phase transition. This strongly suggests the phenomenon of Anderson localization drives the QCD vacuum to the chirally symmetric phase in a way similar to a metal-insulator transition in a disordered conductor. We also discuss how Anderson localization affects the usual phenomenological treatment of phase transitions a la Ginzburg-Landau.

We apply the method of the QCD sum rule, in which positive- and negative-parity baryons couple with each other, to the flavor-octet hyperons and investigate the parity splittings. We also reexamine the nucleon in the method, which was studied in our previous paper, by carefully choosing the Borel weight. Both in the nucleon and hyperon channels the obtained sum rules turn out to have a very good Borel stability and also have a Borel window, an energy region in which the OPE converges and the pole contribution dominates over the continuum contribution. The predicted masses of the positive- and negative-parity baryons reproduce the experimental ones fairly well in the $\Lambda$ and $\Sigma$ channels, if we assign the $\Lambda (1670)$ and the $\Sigma (1620)$ to the parity partners of the $\Lambda$ and the $\Sigma$, respectively. This implies that the $\Lambda (1405)$ is not the parity partner of the $\Lambda$ and may be a flavor-singlet or exotic state. In the $\Xi$ channel, the sum rule predicts the mass of the negative-parity state to be about 1.8 GeV, which leads to two possibilities; one is that the observed state with the closest mass, $\Xi (1690)$, is the parity partner and the other is that the parity partner is not yet found but exists around 1.8 GeV.

It is argued that there is a fundamental momentum cutoff in heavy-to-light transitions, which is caused by possible Cherenkov gluon radiation when an energetic light parton travels through the “brown muck.” The soft-overlap contributions where the partonic momenta configuration is highly asymmetric are disfavored, and the problematic end-point singularities and the double countings are absent in this framework. A simple calculation with a natural scale for the cutoff gives a plausible result for the $B\to \pi$ form factor.

The nonperturbative properties of gauge theories in ${\mathrm{AdS}}_4$ are studied in dual supergravity by including light flavor quarks, which are introduced by a D7-brane embedding. Contrary to the Minkowski and ${\mathrm{dS}}_4$, the dilaton does not play any important dynamical role in the ${\mathrm{AdS}}_4$ case, and the characteristic properties like quark confinement and chiral symmetry breaking are realized mainly due to the geometry ${\mathrm{AdS}}_4$. The possible hadron spectra are also examined, and we find that the meson spectra are well described by the formula given by the field theory in ${\mathrm{AdS}}_4$, but the characteristic mass scale is modified by the gauge interactions for excited states.

$U(N_{\mathrm{C}})$ gauge theory with $N_{\mathrm{F}}$ fundamental scalars admits BPS junctions of domain walls. When the networks/webs of these walls contain loops, their size moduli give localized massless modes. We construct Kähler potential of their effective action. In the large size limit Kähler metric is well approximated by kinetic energy of walls and junctions, which is understood in terms of tropical geometry. Kähler potential can be expressed in terms of hypergeometric functions that are useful to understand small size behavior. Even when the loop shrinks, the metric is regular with positive curvature. Moduli space of a single triangle loop has a geometry between a cone and a cigar.

We model the formation, evolution and astrophysical effects of dark compact Scalar Miniclusters (“ScaMs”). These objects arise when a scalar field, with an axion-like or Higgs-like potential, undergoes a second-order phase transition below the QCD scale. Such a scalar field may couple too weakly to the standard model to be detectable directly through particle interactions, but may still be detectable by gravitational effects, such as lensing and baryon accretion by large, gravitationally bound miniclusters. The masses of these objects are shown to be constrained by the $\mathrm{Ly}\alpha$ power spectrum to be less than $\sim {10}^4{M}_{\odot }$, but they may be as light as classical axion miniclusters, of the order of ${10}^{-12}{M}_{\odot }$. We simulate the formation and nonlinear gravitational collapse of these objects around matter-radiation equality using an $N$-body code, estimate their gravitational lensing properties, and assess the feasibility of studying them using current and future lensing experiments. Future MACHO-type variability surveys of many background sources can reveal either high-amplification, strong-lensing events, or measure density profiles directly via weak-lensing variability, depending on ScaM parameters and survey depth. However, ScaMs, due to their low internal densities, are unlikely to be responsible for apparent MACHO events already detected in the Galactic halo. As a result, in the entire window between ${10}^{-7}{M}_{\odot }$ and ${10}^2{M}_{\odot }$ covered by the galactic scale lensing experiments, ScaMs may in fact compose all the dark matter. A simple estimate is made of parameters that would give rise to early structure formation; in principle, early stellar collapse could be triggered by ScaMs as early as recombination, and significantly affect cosmic reionization.

Precision timing is the key ingredient of ongoing pulsar-based gravitational wave searches and tests of general relativity using binary pulsars. The conventional approach to timing explicitly assumes that the radio emitting region is located at the center of the pulsar, while polarimetric observations suggest that radio emission is in fact produced at altitudes ranging from tens to thousands of kilometers above the neutron star surface. Here we present a calculation of the effects of finite emission height on the timing of binary pulsars using a simple model for the emitting region geometry. A finite height of emission $h$ changes the propagation path of radio photons through the binary and gives rise to a large spin velocity of the emission region corotating with the neutron star. Under favorable conditions these two effects introduce corrections to the conventional time delays at the microsecond level (for a millisecond pulsar in a double neutron star binary with a period of several hours and assuming $h=100\mathrm{km}$). Exploiting the dependence of the emission height on frequency (radius-to-frequency mapping) and using multifrequency observations one should be able to detect these timing corrections even though they are formally degenerate with conventional time delays. Although even in the most accurately timed systems the magnitude of the finite emission height effects is currently somewhat below timing precision, longer-term observations and future facilities like SKA will make measurement of these effects possible, providing an independent check of existing emission height estimates.

We study the rare semileptonic and radiative leptonic $B_s$ decays in the universal extra dimension model. In this scenario, with a single extra dimension, there exists only one new parameter beyond those of the standard model, which is the inverse of the compactification radius $R$. We find that with the additional contributions due to the Kaluza-Klein (KK) modes the branching ratios of the rare $B_s$ decays are enhanced from their corresponding standard model values and the zero point of the forward-backward asymmetries are shifted towards the left.

Topological strings on Calabi-Yau manifolds are known to undergo phase transitions at small distances. We study this issue in the case of perturbative topological strings on local Calabi-Yau threefolds given by a bundle over a two-sphere. This theory can be regarded as a q-deformation of Hurwitz theory, and it has a conjectural nonperturbative description in terms of q-deformed 2D Yang-Mills theory. We solve the planar model and find a phase transition at small radius in the universality class of 2D gravity. We give strong evidence that there is a double-scaled theory at the critical point whose all-genus free energy is governed by the Painlevé I equation. We compare the critical behavior of the perturbative theory to the critical behavior of its nonperturbative description, which belongs to the universality class of 2D supergravity, and we comment on possible implications for nonperturbative 2D gravity. We also give evidence for a new open/closed duality relating these Calabi-Yau backgrounds to open strings with framing.