The predictions of the inflationary $\Lambda \mathrm{CDM}$ paradigm match today’s high-precision measurements of the cosmic microwave background anisotropy extremely well. The same data put tight limits on other sources of anisotropy. Cosmic strings are a particularly interesting alternate source to constrain. Strings are topological defects, remnants of inflationary-era physics that persist after the big bang. They are formed in a variety of models of inflation, including string theory models such as brane inflation. We assume a “Nambu-Goto” model for strings, approximated by a collection of unconnected segments with zero-width, and show that measurements of temperature anisotropy by the South Pole Telescope break a parameter degeneracy in the WMAP data, permitting us to place a strong upper limit on the possible string contribution to the CMB anisotropy: the power sourced by zero-width strings must be $<1.75\%$ (95% CL) of the total or the string tension $G\mu <1.7\times {10}^{-7}$. These limits imply that the best hope for detecting strings in the CMB will come from B-mode polarization measurements at arcminute scales rather than the degree scale measurements pursued for gravitational wave detection.

We solve the Klein-Gordon equation for a massive, nonminimally coupled scalar field, with a conformal coupling, undergoing cosmological evolution from a radiation-dominated phase to a future sudden singularity. We show that, after regularization, the energy of the created particles is zero and the backreaction from quantum effects does not change the evolution of the Universe near the future singularity and cannot prevent the finite-time sudden singularity.

We model the large scale late time universe as a $\Lambda \mathrm{CDM}$ cosmology driven by cosmological constant and perfect dust fluid. Our aim is to find new solutions in the matter and $\Lambda$ epoch consistent with inflationary initial conditions, namely, that to the far past in the matter era the cosmology tends to a flat Friedmann-Lemaître-Robertson-Walker solution. We identify the moduli degrees of freedom that parametrize the flat $\Lambda$-dust Friedmann-Lemaître-Robertson-Walker solution and then promote these moduli to slowly varying functions of the spatial coordinates and show how to solve the Einstein equations in a comoving gradient expansion, controlled by the cosmological constant length scale. Our initial conditions ensure that the approximation remains under control to the far past of the matter era, and to the far future of $\Lambda$ domination. The solution is fully nonperturbative in the amplitude of the metric deformation, and we explicitly construct it to fourth order in derivatives. A general $\Lambda$-dust universe dominated by $\Lambda$ in the future is characterized by a 3-metric and a stress tensor (with positive trace) defined on the future conformal boundary. The new cosmologies with inflationary initial conditions are characterized only by the boundary 3-metric, the stress tensor being locally determined entirely in terms of that metric.

A global monopole (or other topological defect) formed during a recent phase transition with core size comparable to the present Hubble scale, could induce the observed accelerating expansion of the Universe. In such a model, topological considerations trap the scalar field close to a local maximum of its potential in a cosmologically large region of space. We perform detailed numerical simulations of such an inhomogeneous dark energy system (topological quintessence) minimally coupled to gravity, in a flat background of initially homogeneous matter. We find that when the energy density of the field in the monopole core starts dominating the background density, the spacetime in the core starts to accelerate its expansion in accordance to a $\Lambda \mathrm{CDM}$ model with an effective inhomogeneous spherical dark energy density parameter ${\Omega }_{\Lambda }(r)$. The matter density profile is found to respond to the global monopole profile via an anticorrelation (matter underdensity in the monopole core). Away from the monopole core, the spacetime is effectively Einstein-de Sitter (${\Omega }_{\Lambda }(r_{\mathrm{out}})\to 0$) while at the center ${\Omega }_{\Lambda }(r\simeq 0)$ is maximum. We fit the numerically obtained expansion rate at the monopole core to the Union2 data and show that the quality of fit is almost identical to that of $\Lambda \mathrm{CDM}$. Finally, we discuss potential observational signatures of this class of inhomogeneous dark energy models.

We analyze the a set of 17 rotation curves of low surface brightness (LSB) galaxies from The HI Nearby Galaxy Survey (THINGS) with different mass models to study the core structure and to determine a phase transition energy scale ($E_c$) between hot and cold dark matter, due to nonperturbative effects in the bound dark matter (BDM) model. Our results agree with previous ones, implying the cored profiles are preferred over the $N$-body motivated cuspy Navarro-Frenk-White (NFW) profile. We find an average galactic core radius of $r_c=260\times {10}^{\pm 1.3}\mathrm{pc}$ and a phase transition energy $E_c=0.11\times {10}^{\pm 0.46}\mathrm{eV}$, that is of the same order of magnitude as the sum of the neutrino masses.

Recently the ratio of neutron to proton structure functions $F_2^n/F_2^p$ was extracted from a phenomenological correlation between the strength of the nuclear EMC effect and inclusive electron–nucleus cross section ratios at $x>1$. Within conventional models of nuclear smearing, this “in-medium correction” (IMC) extraction constrains the size of nuclear effects in the deuteron structure functions, from which the neutron structure function $F_2^n$ is usually extracted. The IMC data determine the resulting proton $d/u$ quark distribution ratio, extrapolated to $x=1$, to be $0.23\pm 0.09$ with a 90% confidence level. This is well below the SU(6) symmetry limit of $1/2$ and significantly above the scalar diquark dominance limit of 0.

Baryon number violating (BNV) processes are heavily constrained by experiments searching for nucleon decay and neutron-antineutron oscillations. If the baryon number violation occurs via the third generation quarks, however, we may be able to avoid the nucleon stability constraints, thus making such BNV interactions accessible at the LHC. In this paper we study a specific class of BNV extensions of the standard model involving diquark and leptoquark scalars. After an introduction to these models we study one promising extension in detail, being interested in particles with mass of $\mathcal{O}(\mathrm{TeV})$. We calculate limits on the masses and couplings from neutron-antineutron oscillations and dineutron decay for couplings to first and third generation quarks. We explore the possible consequences of such a model on the matter-antimatter asymmetry. We shall see that for models which break the global baryon minus lepton number symmetry ($B-L$), the most stringent constraints come from the need to preserve a matter-antimatter asymmetry. That is, the BNV interaction cannot be introduced if it would remove the matter-antimatter asymmetry independent of baryogenesis mechanism and temperature. Finally, we examine the phenomenology of such models at colliders such as the LHC.

We explore the phenomenology of an extra U(1) gauge boson which primarily couples to standard model gauge bosons. We classify all possible parity-odd couplings up to dimension 6 operators. We then study the prospects for the detection of such a boson at the LHC and show that the electroweak decay channels lead to very clean signals, allowing us to probe couplings well into the TeV scale.

XENON100 and the LHC are two of the most promising machines to test the physics beyond the standard model. In the meantime, indirect hints push us to believe that the dark matter and Higgs boson could be the two next fundamental particles to be discovered. Whereas ATLAS and CMS have just released their new limits on the Higgs searches, XENON100 obtained very recently strong constraints on dark matter–proton elastic scattering. In this work, we show that when we combined WMAP and the most recent results of XENON100, the invisible width of the Higgs to scalar dark matter is negligible ($\lesssim 10\%$), except in a small region with very light dark matter ($\lesssim 10\mathrm{GeV}$) not yet excluded by XENON100 or around 60 GeV where the ratio can reach 50% to 60%. The new results released by the Higgs searches of ATLAS and CMS set very strong limits on the elastic scattering cross section, even restricting it to the region $8\times {10}^{-46}{\mathrm{cm}}^2\lesssim {\sigma }_{S-p}^{\mathrm{SI}}\lesssim 2\times {10}^{-45}{\mathrm{cm}}^2$ in the hypothesis $135\mathrm{GeV}\lesssim M_H\lesssim 155\mathrm{GeV}$.

We present a new solution to the doublet-triplet splitting problem which also works in a supersymmetric $SU(5)$ grand unified theory and is testable at TeV-scale collider experiments. In our model, the $SU(5)$ symmetry is broken through the Hosotani mechanism. Thanks to the phase nature of the Hosotani breaking, the “missing VEV” can be realized even in an $SU(5)$ model. A general and distinctive prediction of this solution is the existence of light adjoint chiral supermultiplets with masses of the supersymmetry-breaking scale. Though these fields disturb the gauge coupling unification, it can be recovered, keeping the unified gauge coupling constant perturbative, by introducing additional vectorlike particles, which may be also observed in the upcoming collider experiments.

A system of two heavy fermions, leptons, or quarks of the fourth generation, which are bound together via the Higgs boson exchange is studied. The conventional Yukawa-type interaction produced by this exchange is accompanied by several important corrections. We derived the Hamiltonian, which describes the correction arising from the retardation (compare the Breit correction in QED); we also calculated the relativistic and radiative corrections. The Higgs-induced bound state appears for the fermion mass $m>m_{\mathrm{cr}}\approx 500\mathrm{GeV}$. When the long-range Coulomb interaction or the gluon exchange is included, the bound states exist for any mass, but the Higgs exchange drastically increases the binding energy of these states when $m$ is approaching $m_{\mathrm{cr}}$. In the region $m>m_{\mathrm{cr}}$ the gluon exchange gives a sizable correction to the Higgs-induced binding energy. This correction greatly exceeds typical binding energies in the states produced via the gluon exchange only. The final results for the binding energies are presented as analytical functions of the Higgs and fermion masses. The possibility of detection of the considered bound states at LHC is discussed.

Under broad assumptions, breaking of Lorentz invariance in gravitational theories leads to tension with unitarity because it allows for processes that apparently violate the second law of thermodynamics. The crucial ingredient of this argument is the existence of black hole solutions with the interior shielded from infinity by a causal horizon. We study how the paradox can be resolved in the healthy extension of Hořava gravity. To this aim we analyze classical solutions describing large black holes in this theory with the emphasis on their causal structure. The notion of causality is subtle in this theory due to the presence of instantaneous interactions. Despite this fact, we find that within exact spherical symmetry a black hole solution contains a space-time region causally disconnected from infinity by a surface of finite area—the “universal horizon.” We then consider small perturbations of arbitrary angular dependence in the black hole background. We argue that aspherical perturbations destabilize the universal horizon and, at the nonlinear level, turn it into a finite-area singularity. The causal structure of the region outside the singularity is trivial. If the higher-derivative terms in the equations of motion smear the singularity while preserving the trivial causal structure of the solutions, the thermodynamics paradox would be obviated. As a by-product of our analysis we prove that the black holes do not have any nonstandard long-range hair. We also comment on the relation with Einstein-aether theory, where the solutions with a universal horizon appear to be stable.

The standard model Higgs boson with large nonminimal coupling to the gravitational curvature can drive cosmological inflation. We study this type of inflationary scenario in the context of supersymmetric grand unification and point out that it is naturally implemented in the minimal supersymmetric $SU(5)$ model, and hence virtually in any GUT models. It is shown that with an appropriate Kähler potential the inflaton trajectory settles down to the standard model vacuum at the end of the slow roll. The predicted cosmological parameters are also consistent with the 7-year WMAP data.

I carry out a finite-size scaling study of the correlation length in SU(3) lattice gauge theory coupled to 12 fundamental flavor fermions, using recent data published by Fodor, Holland, Kuti, Nógradi and Schroeder [Z. Fodor, K. Holland, J. Kuti, D. Nogradi, and C. Schroeder, Phys. Lett. B 703, 348 (2011).]. I make the assumption that the system is conformal in the zero-mass, infinite volume limit, that scaling is violated by both nonzero fermion mass and by finite volume, and that the scaling function in each channel is determined self-consistently by the data. From several different observables I extract a common exponent for the scaling of the correlation length $\xi$ with the fermion mass $m_q$, $\xi \sim m_q^{-1/y_m}$ with $y_m\sim 1.35$. Shortcomings of the analysis are discussed.

Using Lewis-Riesenfeld theory, we derive an exact nonadiabatic master equation describing the time evolution of the QED Schwinger pair-production rate for a general time-varying electric field. This equation can be written equivalently as a first-order matrix equation, as a Vlasov-type integral equation, or as a third-order differential equation. In the last version it relates to the Korteweg-de Vries equation, which allows us to construct an exact solution using the well-known one-soliton solution to that equation. The case of timelike delta function pulse fields is also briefly considered.

We examine the effect of the difference in nuclear interactions of $K^0$ and ${\overline{K}}^0$ mesons on the measurement of $CP$ asymmetry for experiments at $e^{+}{e}^{-}$ colliders—charm and $B$-meson factories. We find that this effect on $CP$ asymmetry can be as large as 0.3%, and therefore sufficiently significant in interpreting measurements of $CP$ asymmetry when neutral kaons are present in the final state.

In previous investigations, it was found that four-sided polygonal lightlike Wilson loops in $\mathcal{N}=6$ super Chern-Simons matter (ABJM) theory calculated to two-loop order have the same form as the corresponding Wilson loop in $\mathcal{N}=4$ SYM at one-loop order. Here we study lightlike polygonal Wilson loops with $n$ cusps in planar three-dimensional Chern-Simons and ABJM theory to two loops. Remarkably, the result in ABJM theory precisely agrees with the corresponding Wilson loop in $\mathcal{N}=4$ SYM at one-loop order for arbitrary $n$. In particular, anomalous conformal Ward identities allow for a so-called remainder function of conformal cross ratios for $n\ge 6$, which is found to be trivial at two loops in ABJM theory in the same way as it is trivial in $\mathcal{N}=4$ SYM at one-loop order. Furthermore, the result for arbitrary $n$ obtained here, allows for a further investigation of a Wilson loop/amplitude duality in ABJM theory, for which nontrivial evidence was recently found by a calculation of four-point amplitudes that match the Wilson loop in ABJM theory.

We use the AdS/CFT correspondence to discuss an equivalence between a helical, strongly coupled Luttinger liquid and a fermion propagating in the background of a topologically charged black hole in three dimensions. The Fermi level is set by the topological charges, thus surmounting difficulties in low dimensions of the standard approach using Coulomb charged black holes. The construction is fully embeddable in string theory, and the microscopic Lagrangian is explicitly known. The retarded Green function at low temperature and energy arises from the geometry very near the black hole horizon, a structure that is universal for all cold, charged liquids with a dual $\mathbb{R}\times \mathrm{U}(1{)}^s$ invariant description in gravity. This explains a subtle relationship between Luttinger physics and the infrared behavior of higher dimensional non-Fermi liquids in the AdS/CFT correspondence.

We compute semiclassical three-point correlation function, or structure constant, of two finite-size (dyonic) giant magnon string states and a light dilaton mode in the Lunin-Maldacena background, which is the $\gamma$-deformed, or $TsT$-transformed ${\mathrm{AdS}}_5\times S_{\gamma }^5$, dual to $\mathcal{N}=1$ super Yang-Mills theory in four dimensions. We also prove that an important relation between the structure constant and the conformal dimension, checked for the $\mathcal{N}=4$ super Yang-Mills case, still holds for the $\gamma$-deformed string background.

The electric permittivity and magnetic permeability for the quark-gluon plasma is calculated within the hard-thermal-loop perturbation theory. The refractive indices in the magnetizable and nonmagnetizable plasmas are calculated. In a magnetizable plasma, there is a frequency pole ${\omega }_{mp}$ in the magnetic permeability and the refractive index. The refractive index becomes negative in the range $\omega \in [k,{\omega }_{mp}]$, where $k$ is the wave number, but no propagating modes are found. In a nonmagnetizable plasma, the magnetic permeability and the refractive index are always positive. This marks the main distinction of a weakly coupled plasma from a strongly coupled one, where the negative refraction is shown to exist in a holographic theory.