We calculate the drag and diffusion coefficients in low temperature QED plasma and go beyond the leading order approximation. The non-Fermi-liquid behavior of these coefficients are clearly revealed. We observe that the subleading contributions due to the exchange of soft transverse photon in both cases are larger than the leading order terms coming from the longitudinal sector. The results are presented in closed form at zero and low temperature.

We investigate new and unusual signals that arise in theories where dark matter is asymmetric and carries a net antibaryon number, as may occur when the dark matter abundance is linked to the baryon abundance. Antibaryonic dark matter can cause induced nucleon decay by annihilating visible baryons through inelastic scattering. These processes lead to an effective nucleon lifetime of ${10}^{29}–{10}^{32}\mathrm{yrs}$ in terrestrial nucleon decay experiments, if baryon number transfer between visible and dark sectors arises through new physics at the weak scale. The possibility of induced nucleon decay motivates a novel approach for direct detection of cosmic dark matter in nucleon decay experiments. Monojet searches (and related signatures) at hadron colliders also provide a complementary probe of weak-scale dark-matter-induced baryon number violation. Finally, we discuss the effects of baryon-destroying dark matter on stellar systems and show that it can be consistent with existing observations.

In this article, we present a simple theoretical framework where the origin of the $\mu$ term and the matter-parity–violating interactions of the minimal supersymmetric standard model can be understood from the spontaneous breaking of new Abelian gauge symmetries. In this context, the masses of the $Z^{\prime }$ gauge bosons, the $M$-parity–violating scale and the $\mu$ term are determined by the supersymmetry breaking scale. The full spectrum of the theory is discussed in detail. We investigate the predictions for the Higgs masses in detail showing that it is possible to satisfy the LEP2 bounds even with sub-TeV squark masses. The model predicts the existence of light colored fields, lepton- and baryon-number violation, and new neutral gauge bosons at the Large Hadron Collider.

Current limits from the LHC on fourth generation quarks are already at the unitarity bound of 500 GeV or so. If they exist, the strong Yukawa couplings are turning nonperturbative, and may form bound states. We study the domain of $m_{b^{\prime }}$ and $m_{t^{\prime }}$ in the range of 500 to 700 GeV, where we expect binding energies are mainly of Yukawa origin, with QCD subdominant. To be consistent with electroweak precision tests, the $t^{\prime }$ and $b^{\prime }$ quarks have to be nearly degenerate, exhibiting a new “isospin.” Comparing relativistic expansion with a relativistic bound state approach, we find the most interesting is the production of a color octet, isosinglet vector meson (a “gluon-prime”) via $q\overline{q}\to {\omega }_8$. Leading decay modes are ${\pi }_8^{\pm }{W}^{\mp }$, ${\pi }_8^0{Z}^0$, and constituent quark decay, with $q\overline{q}$ and $t{\overline{t}}^{\prime }$ and $b{\overline{b}}^{\prime }$ subdominant. The color octet, isovector pseudoscalar ${\pi }_8$ meson decays via constituent quark decay, or to $Wg$. These decay rates are parameterized by the decay constant, the binding energy and mass differences, and $V_{t{b}^{\prime }}$. For small $V_{t^{\prime }b}$, one could have a spectacular signal of $WWg$, where a soft $W$ accompanies a very massive $Wg$ pair. In general, however, one has high multiplicity signals with $b$, $W$, and $t$ jet substructures that are not so different from the $t^{\prime }{\overline{t}}^{\prime }$ and $b^{\prime }{\overline{b}}^{\prime }$ search.

We consider the production and detection of a sequential, down type quark via the mode $pp\to b^{\prime }{\overline{b}}^{\prime }\to W^{+}{W}^{-}t\overline{t}\to \ell {\nu }_{\ell }8j$ at the LHC, with the collision energy $\sqrt{s}=10\mathrm{TeV}$ and the total integrated luminosity around $1{\mathrm{fb}}^{-1}$. We assume $m_{b^{\prime }}=m_{t^{\prime }}=600\mathrm{GeV}$. A full reconstruction is employed and the signal and background discrimination is studied within a neural network approach. Our results show that this mode can make a useful contribution to the $b^{\prime }$ search.

We continue our study of algebraic properties of $\mathcal{N}=4$ topological amplitudes in heterotic string theory compactified on ${\mathbb{T}}^2$, initiated in arXiv:1102.1821. In this work we evaluate a particular one-loop amplitude for any enhanced gauge group $\mathfrak{h}\subset {\mathfrak{e}}_8\oplus {\mathfrak{e}}_8$, i.e. for arbitrary choice of Wilson line moduli. We show that a certain analytic part of the result has an infinite product representation, where the product is taken over the positive roots of a Lorentzian Kac-Moody algebra ${\mathfrak{g}}^{++}$. The latter is obtained through double extension of the complement $\mathfrak{g}=({\mathfrak{e}}_8\oplus {\mathfrak{e}}_8)/\mathfrak{h}$. The infinite product is automorphic with respect to a finite index subgroup of the full $T$-duality group $SO(2,18;\mathbb{Z})$ and, through the philosophy of Borcherds-Gritsenko-Nikulin, this defines the denominator formula of a generalized Kac-Moody algebra $\mathcal{G}({\mathfrak{g}}^{++})$, which is an ’automorphic correction’ of ${\mathfrak{g}}^{++}$. We explicitly give the root multiplicities of $\mathcal{G}({\mathfrak{g}}^{++})$ for a number of examples.

We consider a four-dimensional field-theory model with two massless fermions, coupled to an Abelian vector field without flavor mixing, and to another Abelian vector field with flavor mixing. Both Abelian vectors have a Lorentz-violating kinetic term, introducing a Lorentz-violation mass scale $M$, from which fermions and the flavor-mixing vector get their dynamical masses, whereas the vector coupled without flavor mixing remains massless. When the two coupling constants have similar values in order of magnitude, a mass hierarchy pattern emerges, in which one fermion is very light compared to the other, while the vector mass is of the order of the heavy fermion mass. The work presented here may be considered as a Lorentz-symmetry-violating alternative to the Higgs mechanism, in the sense that no scalar particle (fundamental or composite) is necessary for the generation of the vector-meson mass. However, the model is not realistic given that, as a result of Lorentz violation, the maximal (light-cone) speed seen by the fermions is smaller than that of the massless gauge boson (which equals the speed of light in vacuo) by an amount which is unacceptably large to be compatible with the current tests of Lorentz invariance, unless the gauge couplings assume unnaturally small values. Possible ways out of this phenomenological drawback are briefly discussed, postponing a detailed construction of more realistic models for future work.

The CDF Collaboration recently presented evidence for an excess in the dijet invariant mass distribution coming from events in a $W+2j$ exclusive sample. Here we show that this excess can be explained by the $s$-channel production of a weakly coupled Higgsophilic $Z^{\prime }$ near $M_{Z^{\prime }}\sim 270\mathrm{GeV}$ which decays into a $W^{\pm }$ and a charged Higgs at $M_{H^{\pm }}\sim 150\mathrm{GeV}$. While the simplest implementations of a general leptophobic $Z^{\prime }$ model quickly run into tensions with electroweak observables, a more specific Higgsophilic model evades these constraints without resorting to any fine-tuning. We discuss the distinctive features of this model, focusing on its particular signatures at the Tevatron.

The Witten-Sakai-Sugimoto construction of holographic QCD in terms of D4 color branes and D8 flavor branes in type IIA string theory is used to investigate the role of topological charge in the chiral dynamics of quarks in QCD. The QCD theta term arises from a compactified five-dimensional Chern-Simons term on the D4 branes. This term couples the QCD topological charge to the Ramond-Ramond (RR) $U(1)$ gauge field of type IIA string theory. For large $N_c$ the contribution of instantons (D0 branes) is suppressed, and the nonzero topological susceptibility of pure-glue QCD is attributed to the presence of D6 branes, which constitute magnetic sources of the RR gauge field. The topological charge of QCD is required, by an anomaly inflow argument, to coincide in space-time with the intersection of the D6 branes and the D4 color branes. This clarifies the relation between D6 branes and the coherent, codimension-one topological charge membranes observed in QCD Monte Carlo calculations. Using open-string/closed-string duality, we interpret a quark loop (represented by a D4-D8 open-string loop) in terms of closed-string exchange between color and flavor branes. The role of the RR gauge field in quark-antiquark annihilation processes is discussed. RR exchange in the s-channel generates a 4-quark contact term which produces an ${\eta }^{\prime }$ mass insertion and provides an explanation for the observed spin-parity structure of the Okubo-Zweig-Iizuka rule. The $(\log \mathrm{DetU}{)}^2$ form of the $U(1)$ anomaly emerges naturally. RR exchange in the t-channel of the $q\overline{q}$ scattering amplitude produces a Nambu–Jona-Lasinio interaction which may provide a mechanism for spontaneous breaking of $SU(N_f)\times SU(N_f)$.

Our recent method to calculate renormalized functional determinants, the partial-wave cutoff method, is extended for the evaluation of 4-D fermion one-loop effective action with arbitrary mass in certain types of radially symmetric, non-Abelian, background gauge fields (including instantonlike and instanton-antiinstanton-like configurations). A detailed study on functional determinants for matrix-valued radial differential operators is presented, explicating both our analytic treatment on the high partial-wave contribution and the application of the generalized Gel’fand-Yaglom formula to determine the low partial-wave contribution. In general, some numerical work is needed for the low partial-wave part. In the massless limit, however, the factorizable nature of our partial-wave radial differential operators can be exploited to evaluate semianalytically even the low partial-wave part, and we thus have the full fermion effective action calculated explicitly in a class of non-Abelian background gauge fields. With nonzero mass, we also perform necessary numerical analysis as regards the low partial-wave contribution to produce numerically exact results for the massive effective action. Comparing these against the results of the large mass expansion, the validity range of the large mass expansion is addressed. Also studied are possible quantum deformation of instanton into a non-self-dual configuration and the fermion mass dependence of the effective instanton-antiinstanton interaction, based on the fermion effective action we evaluated.

We calculate the total internal energy, total energy density and pressure, and the free energy for the neutrino and electromagnetic fields in Einstein and closed Friedmann cosmological models. The Casimir contributions to all these quantities are separated. The asymptotic expressions for both the total internal energy and free energy, and for the Casimir contributions to them are found in the limiting cases of low and high temperatures. It is shown that the neutrino field does not possess a classical limit at high temperature. As for the electromagnetic field, we demonstrate that the total internal energy has the classical contribution and the Casimir internal energy goes to the classical limit at high temperature. The respective Casimir free energy contains both linear and logarithmic terms with respect to the temperature. The total and Casimir entropies for the neutrino and electromagnetic fields at low temperature are also calculated and shown to be in agreement with the Nernst heat theorem.

Black-hole spacetimes with a photonsphere, a hypersurface on which massless particles can orbit the black hole on circular null geodesics, are studied. We prove that among all possible trajectories (both geodesic and nongeodesic) which circle the central black hole, the null circular geodesic is characterized by the shortest possible orbital period as measured by asymptotic observers. Thus, null circular geodesics provide the fastest way to circle black holes. In addition, we conjecture the existence of a universal lower bound for orbital periods around compact objects (as measured by flat-space asymptotic observers): $T_{\infty }\ge 4\pi M$, where $M$ is the mass of the central object. This bound is saturated by the null circular geodesic of the maximally rotating Kerr black hole.

We consider a self-gravitating system consisting of perfect fluid with spherical symmetry. Using the general expression of entropy density, we extremize the total entropy $S$ under the constraint that the total number of particles is fixed. We show that extrema of $S$ coincides precisely with the relativistic Tolman-Oppenheimer-Volkoff equation of hydrostatic equilibrium. Furthermore, we apply the maximum entropy principle to a charged perfect fluid and derive the generalized Tolman-Oppenheimer-Volkoff equation. Our work provides strong evidence for the fundamental relationship between general relativity and ordinary thermodynamics.

We study the transition from an emergent Galileon condensate phase of the early universe to a later expanding radiation phase. This defrosting or preheating transition is a consequence of the excitation of matter fluctuations by the coherent Galileon condensate, in analogy to how preheating in inflationary cosmology occurs via the excitation of matter fluctuations through coupling of matter with the coherent inflaton condensate. We show that the minimal coupling of matter (modeled as a massless scalar field) to the Galileon field introduced by Creminelli, Nicolis, and Trincherini in order to generate a scale-invariant spectrum of matter fluctuations is sufficient to lead to efficient defrosting, provided that the effects of the nonvanishing expansion rate of the universe are taken into account. If we neglect the effects of expansion, an additional coupling of matter to the Galileon condensate is required. We study the efficiency of the defrosting mechanism in both cases.

We show that in supersymmetry one can obtain inflationary potentials in the observable sector that are sufficiently flat at sub-Planckian field values. Structure of the supersymmetric scalar potential along a flat direction combined with the existence of higher order terms in an effective field theory expansion allows one to find scales below the effective field theory cutoff where two or a higher number of the potential derivatives may vanish. As an explicit example, we demonstrate that inflection point inflation within a broad range of scales $\mathcal{O}(\mathrm{TeV})\ll H_{\inf }<3\times {10}^9\mathrm{GeV}$ can be accommodated within weak scale supersymmetry. The fine tuning of model parameters needed for successful inflation is considerably improved in this scenario.

We have shown that the $B\mathrm{\text{−}}L$ generation due to the decay of the thermally produced superheavy fields can explain the Baryon asymmetry in the Universe if the superheavy fields are heavier than ${10}^{13-14}\mathrm{GeV}$. Note that, although the superheavy fields have nonvanishing charges under the standard model gauge interactions, the thermally produced baryon asymmetry is sizable. The $B\mathrm{\text{−}}L$–violating effective operators induced by integrating the superheavy fields have dimension 7, while the operator in the famous leptogenesis has dimension 5. Therefore, the constraints from the nucleon stability can be easily satisfied.

The leading $1/N_c$ behavior of unitarized chiral perturbation theory distinguishes the nature of the $\rho$ and the $\sigma$: The $\rho$ is a $\overline{q}q$ meson, while the $\sigma$ is not. However, semilocal duality between resonances and Regge behavior cannot be satisfied for larger $N_c$, if such a distinction holds. While the $\sigma$ at $N_c=3$ is inevitably dominated by its di-pion component, unitarized chiral perturbation theory also suggests that as $N_c$ increases above 6–8, the $\sigma$ may have a subdominant $\overline{q}q$ fraction up at 1.2 GeV. Remarkably this ensures semilocal duality is fulfilled for the range of $N_c\lesssim 15–30$, where the unitarization procedure adopted applies.

The search for a standard model Higgs boson with the $H\to W{W}^{(*)}\to \ell \ell +E_T^{\mathrm{miss}}$ decay and the application of a full-jet veto yields a strong sensitivity in the mass range $130<m_H<200\mathrm{GeV}$. One of the residual backgrounds is related to processes involving top quarks. A method for the extraction of top backgrounds is evaluated at the parton and hadronic levels based on the data-driven extraction of the jet veto survival probability. The dominant systematic uncertainty of the proposed method is estimated to be about 15%.

We derive limits on the interactions of dark matter with quarks from ATLAS null searches for $\mathrm{\text{jets}}+\mathrm{\text{missing energy}}$ based on $\sim 1{\mathrm{fb}}^{-1}$ of integrated luminosity, using a model-insensitive effective theory framework. We find that the new limits from the LHC significantly extend limits previously derived from CDF data at the Tevatron. Translated into the parameter space of direct searches, these limits are particularly effective for $\sim \mathrm{GeV}$ mass weakly interacting massive particles. Our limits indicate tension with isospin-violating models satisfying minimal flavor violation which attempt to reconcile the purported CoGeNT excess with Xenon-100, indicating that either a light mediator or nontrivial flavor structure for the dark sector is necessary for a viable reconciliation of CoGeNT with Xenon.

We present calculations of axial-current matrix elements between various heavy-meson and heavy-baryon states to the next-to-leading order in heavy-hadron chiral perturbation theory in the $p$-regime. When compared with data from lattice computations or experiments, these results can be used to determine the axial couplings in the chiral Lagrangian. Our calculation is performed in partially quenched chiral perturbation theory for both $\mathrm{SU}(4|2)$ and $\mathrm{SU}(6|3)$. We incorporate finite-size effects arising from a single Goldstone meson wrapping around the spatial volume. Results for full QCD with two and three flavors can be obtained straightforwardly by taking the sea-quark masses to be equal to the valence-quark masses. To illustrate the impact of our chiral perturbation theory calculation on lattice computations, we analyze the SU(2) full-QCD results in detail. We also study one-loop contributions relevant to the heavy-hadron strong-decay amplitudes involving final-state Goldstone bosons, and demonstrate that the quark-mass dependence of these amplitudes can be significantly different from that of the axial-current matrix elements containing only single-hadron external states.