We give a technique for calculating the occupation number of quantum fields in time-dependent backgrounds by using the relation between one-dimensional quantum oscillators and two-dimensional classical oscillators. We illustrate our method by giving closed analytical results for the time-dependent spectrum of occupation numbers during gravitational collapse in any number of dimensions.

We consider two aspects of scattering in strong plane-wave backgrounds. First, we show that the infrared divergences in elastic scattering depend on the structure of the background, but can be removed using the usual Bloch-Nordsieck approach. Second, we analyze the infinite series of shifted-mass-shell poles in the particle (Volkov) propagator using lightfront quantization. The complete series of poles is shown to describe a single, on-shell, propagating particle.

Considering the quantum statistics of the degrees of freedom on the holographic screen, it is shown that the ratio of the number of excited bulk degrees of freedom to the number of excited surface degrees of freedom is given by the modified Newtonian dynamics (MOND) interpolating function $\tilde{\mu }$. This relationship is shown to hold also in aquadratic Lagrangian theory and in the extension of MOND to de Sitter space. Based on the relationship between the entropy and the number of degrees of freedom on the holographic screen, a simple expression, relating the MOND interpolating function to the ratio of the two-dimensional entropy to Bekenstein-Hawking entropy, is obtained. In terms of this expression MOND can be viewed as a modification of gravity arising due to a bound on the maximum entropy for the holographic screen.

Amongst the multitude of inflationary models currently available, models that lead to features in the primordial scalar spectrum are drawing increasing attention, since certain features have been found to provide a better fit to the cosmic microwave background data than the conventional, nearly scale invariant, primordial spectrum. In this work, we carry out a complete numerical analysis of two models that lead to oscillations over all scales in the scalar power spectrum. We consider the model described by a quadratic potential which is superposed by a sinusoidal modulation and the recently popular axion monodromy model. Since the oscillations continue even on to arc minute scales, in addition to the WMAP data, we also compare the models with the small scale data from ACT. Though, both the models, broadly, result in oscillations in the spectrum; interestingly, we find that, while the monodromy model leads to a considerably better fit to the data in comparison to the standard power law spectrum, the quadratic potential superposed with a sinusoidal modulation does not improve the fit to a similar extent. We also carry out forecasting of the parameters using simulated Planck data for both the models. We show that the Planck mock data performs better in constraining the model parameters as compared to the presently available cosmic microwave background datasets.

The velocity distribution function (VDF) of the hypothetical weakly interacting massive particles (WIMPs), currently the most favored candidate for the dark matter in the Galaxy, is determined directly from the circular speed (“rotation”) curve data of the Galaxy assuming isotropic VDF. This is done by “inverting”—using Eddington’s method—the Navarro-Frenk-White universal density profile of the dark matter halo of the Galaxy, the parameters of which are determined by using the Markov chain Monte Carlo technique from a recently compiled set of observational data on the Galaxy’s rotation curve extended to distances well beyond the visible edge of the disk of the Galaxy. The derived most-likely local isotropic VDF strongly differs from the Maxwellian form assumed in the “standard halo model” customarily used in the analysis of the results of WIMP direct-detection experiments. A parametrized (non-Maxwellian) form of the derived most-likely local VDF is given. The astrophysical “g factor” that determines the effect of the WIMP VDF on the expected event rate in a direct-detection experiment can be lower for the derived most-likely VDF than that for the best Maxwellian fit to it by as much as 2 orders of magnitude at the lowest WIMP mass threshold of a typical experiment.

It is shown that a disformally coupled theory in which the gravitational sector has the Einstein-Hilbert form is equivalent to a quartic Dirac-Born-Infeld Galileon Lagrangian, possessing nonlinear higher derivative interactions, and hence allowing for the Vainshtein effect. This Einstein frame description considerably simplifies the dynamical equations and highlights the role of the different terms. The study of highly dense, nonrelativistic environments within this description unravels the existence of a disformal screening mechanism, while the study of static vacuum configurations reveals the existence of a Vainshtein radius, at which the asymptotic solution breaks down. Disformal couplings to matter also allow the construction of dark energy models, which behave differently than conformally coupled ones and introduce new effects on the growth of large scale structure over cosmological scales, on which the scalar force is not screened. We consider a simple disformally coupled dark matter model in detail, in which standard model particles follow geodesics of the gravitational metric and only dark matter is affected by the disformal scalar field. This particular model is not compatible with observations in the linearly perturbed regime. Nonetheless, disformally coupled theories offer enough freedom to construct realistic cosmological scenarios, which can be distinguished from the standard model through characteristic signatures.

Recent LHC results indicate a suppression of jet fragmentation functions in Pb-Pb collisions at intermediate values of $\xi =\ln (1/z)$. This seems to contradict the picture of energy loss based on the induced QCD radiation that is expected to lead to the enhancement of in-medium fragmentation functions. We use an effective $1+1$ dimensional quasi-Abelian model to describe the dynamical modification of jet fragmentation in the medium. We find that this approach describes the data, and argue that there is no contradiction between the LHC results and the picture of QCD radiation induced by the in-medium scattering of the jet. The physics that underlies the suppression of the in-medium fragmentation function at intermediate values of $\xi =\ln (1/z)$ is the partial screening of the color charge of the jet by the comoving medium-induced gluon.

The heavy baryon ${\Lambda }_Q$ ($Q=b$ or $c$) can be regarded as composed of a heavy quark and a scalar light diquark, which has good spin and isospin quantum numbers. In this picture we establish the Bethe-Salpeter equation for ${\Lambda }_Q$ to second order in the $1/m_Q$ expansion. With the kernel containing both the scalar confinement and the one-gluon-exchange terms we solve the Bethe-Salpeter equation numerically. The value of the spin-dependant form factor for the matrix element $⟨{\Lambda }_b(v,s)|\overline{b}{\gamma }^{\lambda }{\gamma }_{5}b|{\Lambda }_b(v,s)⟩$, ${ϵ}_b$, which is nonzero at order $1/m_b^2$, is obtained numerically from our model.

Supersymmetric $SU(5)$ GUT augmented with anomaly-free $U(1{)}_F$ flavor symmetry is presented. A very economical field content and $U(1{)}_F$ charge assignment are obtained by specific construction. In particular, three families of $10+\overline{5}$ chiral matter, along with the $SU(5)$ singlet states (some of which serve as right-handed neutrinos) are obtained. Appealing texture zero Yukawa matrices provide a natural understanding of hierarchies between charged fermion masses and mixings. The model predicts an inverted hierarchical neutrino mass scenario with interesting implications.

The inert Higgs model is a minimal extension of the Standard Model that features a viable dark matter candidate, the so-called inert Higgs ($H^0$). In this paper, we compute and analyze the dominant electroweak corrections to the direct detection cross section of dark matter within this model. These corrections arise from one-loop diagrams mediated by gauge bosons that, contrary to the tree-level result, do not depend on the unknown scalar coupling $\lambda$. We study in detail these contributions and show that they can modify in a significant way the prediction of the spin-independent direct detection cross section. In both viable regimes of the model, $M_{H^0}<M_W$ and $M_{H^0}\gtrsim 500\mathrm{GeV}$, we find regions where the cross section at one loop is much larger than at tree level. We also demonstrate that, over the entire viable parameter space of this model, these new contributions bring the spin-independent cross section within the reach of future direct detection experiments.

We present an explicit model where the decay of an $R$-parity-even scalar $S$ with $\mathcal{O}(\mathrm{TeV})$ mass is the origin of nonthermal dark matter. The correct relic abundance can be produced for both large and small annihilation rates in accordance with the Fermi constraints on the annihilation cross section. This scenario has advantages over that of nonthermal dark matter from modulus decay. First, the branching ratio for production of $R$-parity odd particles can be made quite small by a combination of $S$ couplings to matter fields and kinematic suppression, enabling us to obtain the observed dark matter relic density in cases of thermal underproduction as well as overproduction. Second, gravitino production is naturally suppressed by the virtue of a decaying scalar belonging to the visible sector. The decaying scalar can also successfully generate the baryon asymmetry of the Universe, and may provide an explanation for the baryon—dark matter coincidence puzzle.

We extend our previous study of the SU(3) gauge theory with $N_f=2$ flavors of fermions in the sextet representation of color. Our tool is the Schrödinger functional method. By changing the lattice action, we push the bulk transition of the lattice theory to stronger couplings and thus reveal the beta function and the mass anomalous dimension ${\gamma }_m$ over a wider range of coupling, out to $g^2\simeq 11$. Our results are consistent with an infrared fixed point, but walking is not ruled out. Our main result is that ${\gamma }_m$ never exceeds 0.45, making the model unsuitable for walking technicolor. We use a novel method of extrapolation to the large-volume/continuum limit, tailored to near-conformal theories.

$B\to {\chi }_{c1}(1P,2P)K$ decays are studied in QCD factorization by treating charmonia as nonrelativistic bound states. No infrared divergences exist in the vertex corrections, while the logarithmic end-point singularities in the hard spectator corrections can be regularized by a momentum cutoff. Within certain uncertainties, we find that the $B\to {\chi }_{c1}(2P)K$ decay rate can be comparable to $B\to {\chi }_{c1}(1P)K$ and get $\mathrm{Br}(B^0\to {\chi }_{c1}^{\prime }{K}^0)=\mathrm{Br}(B^{+}\to {\chi }_{c1}^{\prime }{K}^{+})\approx (2–4)\times {10}^{-4}$. This might imply a possible interpretation for the newly discovered X(3872): that this state has a dominant $J^{PC}=1^{++}(2P)$ $c\overline{c}$ component, but it is mixed with a substantial $D^0{\overline{D}}^{*0}+D^{*0}{\overline{D}}^0$ component.

A model is developed to describe odd-parity baryon resonances generated dynamically through a unitary baryon-meson coupled-channels approach. The scheme applies to channels with light- and/or heavy-quark content. Distinct features of the model are that i) the interaction is an $S$-wave contact one, ii) it reduces to the SU(3) Weinberg-Tomozawa Hamiltonian when light pseudoscalar mesons are involved, thus respecting chiral symmetry, iii) spin-flavor is preserved in the light-quark sector, and iv) heavy-quark spin symmetry is fulfilled in the heavy-quark sector. In particular, baryon-meson states with different content in $c$ or in $\overline{c}$ do not mix. The model is a minimal one and it contains no free parameters. In this work, we focus on baryon resonances with hidden charm (at least one $\overline{c}$ and one $c$ quark). We analyze several possible sectors and, for the sector with zero net charm, we write down the most general Lagrangian consistent with SU(3) and heavy-quark spin symmetry. We explicitly study the $N$ and $\Delta$ states, which are produced from the $S$-wave interaction of pseudoscalar and vector mesons with $1/2^{+}$ and $3/2^{+}$ baryons within the charmless and strangeless hidden-charm sector. We predict seven odd-parity $N$-like and five $\Delta$-like states with masses around 4 GeV, most of them as bound states. These states form heavy-quark spin multiplets, which are almost degenerate in mass. The predicted new resonances definitely cannot be accommodated by quark models with three constituent quarks and they might be looked for in the forthcoming PANDA experiment at the future FAIR facility.

The production of heavy sterile neutrinos from ${\pi }^{-}$, $K^{-}$ decay at rest yields charged leptons with negative helicity (positive for ${\pi }^{+}$, $K^{+}$). We obtain the branching ratio for this process and argue that a Stern-Gerlach filter with a magnetic field gradient leads to spatially separated domains of both helicity components with abundances determined by the branching ratio. Complemented with a search of the monochromatic peak, this setup can yield both the mass and mixing angles for sterile neutrinos with masses in the range $3\mathrm{MeV}\lesssim m_s\lesssim 414\mathrm{MeV}$ in next generation high intensity experiments. We also study oscillations of light Dirac and Majorana sterile neutrinos with $m_s\simeq \mathrm{eV}$ produced in meson decays including decoherence aspects arising from lifetime effects of the decaying mesons and the stopping distance of the charged lepton in short baseline experiments. We obtain the transition probability from production to detection via charged current interactions including these decoherence effects for $3+1$ and $3+2$ scenarios, also studying $|\Delta L|=2$ transitions from $\overline{\nu }\leftrightarrow \nu$ oscillations for Majorana neutrinos and the impact of these effects on the determination of $CP$-violating amplitudes. We argue that decoherence effects are important in current short baseline accelerator experiments, leading to an underestimate of masses, mixing and $CP$-violating angles. At MiniBooNE/SciBooNE we estimate that these effects lead to an $\sim 15\%$ underestimate for sterile neutrino masses $m_s\gtrsim 3\mathrm{eV}$. We argue that reactor and current short baseline accelerator experiments are fundamentally different and suggest that in future high intensity experiments with neutrinos produced from $\pi$, $K$ decay at rest, stopping the charged leptons on distances much smaller than the decay length of the parent meson suppresses considerably these decoherence effects.

Based on experimental data by the Belle Collaboration, we present a phenomenological analysis of the angular distributions in ${\tau }^{-}\to K_S{\pi }^{-}{\nu }_{\tau }$ decay. Our study shows that the angular analysis could lead to some interesting observables, and the future experimental investigation of these observables might be very helpful in revealing the nature of the scalar components of the decay. New physics contributions from the two-Higgs-doublet model to this decay have also been examined.

The decay $B_c^{+}\to \psi (2S){\pi }^{+}$ with $\psi (2S)\to {\mu }^{+}{\mu }^{-}$ is observed with a significance of $5.2\sigma$ using $pp$ collision data corresponding to an integrated luminosity of $1.0{\mathrm{fb}}^{-1}$ collected by the LHCb experiment. The branching fraction of $B_c^{+}\to \psi (2S){\pi }^{+}$ decays relative to that of the $B_c^{+}\to J/\psi {\pi }^{+}$ mode is measured to be $\frac{\mathcal{B}(B_c^{+}\to \psi (2S){\pi }^{+})}{\mathcal{B}(B_c^{+}\to J/\psi {\pi }^{+})}=0.250\pm 0.068(\mathrm{stat})\pm 0.014(\mathrm{syst})\pm 0.006(\mathcal{B})$. The last term is the uncertainty on the ratio $\mathcal{B}(\psi (2S)\to {\mu }^{+}{\mu }^{-})/\mathcal{B}(J/\psi \to {\mu }^{+}{\mu }^{-})$.

We develop a general formalism for a nonperturbative treatment of harmonic-oscillator particle detectors in relativistic quantum field theory using continuous-variable techniques. By means of this we forgo perturbation theory altogether and reduce the complete dynamics to a readily solvable set of first-order, linear differential equations. The formalism applies unchanged to a wide variety of physical setups, including arbitrary detector trajectories, any number of detectors, arbitrary time-dependent quadratic couplings, arbitrary Gaussian initial states, and a variety of background spacetimes. As a first set of concrete results, we prove nonperturbatively—and without invoking Bogoliubov transformations—that an accelerated detector in a cavity evolves to a state that is very nearly thermal with a temperature proportional to its acceleration, allowing us to discuss the universality of the Unruh effect. Additionally we quantitatively analyze the problems of considering single-mode approximations in cavity field theory and show the emergence of causal behavior when we include a sufficiently large number of field modes in the analysis. Finally, we analyze how the harmonic particle detector can harvest entanglement from the vacuum. We also study the effect of noise in time-dependent problems introduced by suddenly switching on the interaction versus ramping it up slowly (adiabatic activation).

In the present work, we study the warm tachyon inflation model in the context of “logamediate inflation,” where the cosmological scale factor expands as $a=a_0\exp (A[\ln t{]}^{\lambda })$. The characteristics of this model in slow-roll approximation are presented in the following two cases: (1) The dissipative parameter $\Gamma$ is a function of the tachyon field $\varphi$ and (2) $\Gamma$ is a constant parameter. The level of non-Gaussianity of this model is found for these two cases. Scalar and tensor perturbations for this scenario are presented. The parameters appearing in our model are constrained by recent observational data (WMAP7). Harrison-Zeldovich spectrum, i.e., $n_s=1$, is approximately obtained for large values of $\lambda$ (i.e., $\lambda \simeq 50$) and for normal values of the number of e-folds, i.e., $N\simeq 60$. On the other hand, the scale invariant spectrum (Harrison-Zeldovich spectrum) is given by using two parameters in our model. For intermediate inflation, where the cosmological scale factor expands as $a=a_0\exp (A{t}^f)$, this spectrum has been exactly obtained using one parameter, i.e., $f=\frac{2}{3}$ M. R. Setare and V. Kamali, J. Cosmol. Astropart. Phys. 08 (2012) 034.

From a combination of probes including the cosmic microwave background ($\mathrm{WMAP}7+\mathrm{SPT}$), Hubble constant (HST), baryon acoustic oscillations ($\mathrm{SDSS}+2\mathrm{dFGRS}$), and supernova distances (Union2), we have explored the extent to which the constraints on the effective number of neutrinos and sum of neutrino masses are affected by our ignorance of other cosmological parameters, including the curvature of the universe, running of the spectral index, primordial helium abundance, evolving late-time dark energy, and early dark energy. In a combined analysis of the effective number of neutrinos and sum of neutrino masses, we find mild ($2.2\sigma$) preference for additional light degrees of freedom. However, the effective number of neutrinos is consistent with the canonical expectation of three massive neutrinos and no extra relativistic species to within $1\sigma$ when allowing for evolving dark energy and relaxing the strong inflation prior on the curvature and running. The agreement improves with the possibility of an early dark energy component, itself constrained to be less than 5% of the critical density (95% C.L.) in our expanded parameter space. In extensions of the standard cosmological model, the derived amplitude of linear matter fluctuations ${\sigma }_8$ is found to closely agree with low-redshift cluster abundance measurements. The sum of neutrino masses is robust to assumptions of the effective number of neutrinos, late-time dark energy, curvature, and running at the level of 1.2 eV (95% C.L.). The upper bound degrades to 2.0 eV (95% C.L.) when further including the early dark energy density and primordial helium abundance as additional free parameters. Even in extended cosmological parameter spaces, Planck alone could determine the possible existence of extra relativistic species at $4\sigma$ confidence and constrain the sum of neutrino masses to 0.2 eV (68% C.L.).