We study a novel proposal for the origin of cosmological cold dark matter (CDM) which is rooted in the quantum nature of spacetime. In this model, off-shell modes of quantum fields can exist in asymptotic states as a result of spacetime nonlocality (expected in generic theories of quantum gravity) and play the role of CDM, which we dub off-shell dark matter ($\mathrm{O}f\mathrm{DM}$). However, their rate of production is suppressed by the scale of nonlocality (e.g. Planck length). As a result, we show that $\mathrm{O}f\mathrm{DM}$ is only produced in the first moments of big bang, and then effectively decouples (except through its gravitational interactions). We examine the observational predictions of this model: In the context of cosmic inflation, we show that this proposal relates the reheating temperature to the inflaton mass, which narrows down the uncertainty in the number of $e$-foldings of specific inflationary scenarios. We also demonstrate that $\mathrm{O}f\mathrm{DM}$ is indeed cold, and discuss potentially observable signatures on small scale matter power spectrum.

We investigate whether transition radiation from a particle shower crossing the interface between Earth and air and induced by an Earth-skimming neutrino can explain the upward event announced recently by the ANITA Collaboration. While the properties of the observed signal can in principle be explained with transition radiation, a conservative upper limit on the experiment’s aperture for this kind of signal shows that the flux necessary for a successful explanation is in tension with the current best limits from the Pierre Auger Observatory, the IceCube neutrino detector, and the ANITA balloon. We also show that in this scenario, the direction of the incoming neutrino is determined precisely to within a few degrees, combining the polarization properties of the observed events with the Earth opacity to ultrahigh energy neutrinos.

The first direct observations of gravitational waves have been made by the Advanced LIGO detectors. However, the quest to improve the sensitivities of these detectors remains, and epitaxially grown single-crystal coatings show considerable promise as alternatives to the ion-beam sputtered amorphous mirror coatings typically used in these detectors and other such precision optical measurements. The mechanical loss of a $1\mu \mathrm{m}$ thick single-crystalline gallium phosphide (GaP) coating, incorporating a buffer layer region necessary for the growth of high quality epitaxial coatings, has been investigated over a broad range of frequencies and with fine temperature resolution. It is shown that at 20 K the mechanical loss of GaP is a factor of 40 less than an undoped tantala film heat-treated to $600°\mathrm{C}$ and is comparable to the loss of a multilayer GaP/AlGaP coating. This is shown to translate into possible reductions in coating thermal noise of a factor of 2 at 120 K and 5 at 20 K over the current best IBS coatings (alternating stacks of silica and titania-doped tantala). There is also evidence of a thermally activated dissipation process between 50 and 70 K.

We investigate the consequence of vector leptoquarks on the rare semileptonic lepton flavor violating decays of the $B$ meson which are more promising and effective channels to probe the new physics signal. We constrain the resulting new leptoquark parameter space by using the branching ratios of $B_{s,d}\to l^{+}{l}^{-}$, $K_L\to l^{+}{l}^{-}$ and ${\tau }^{-}\to l^{-}\gamma$ processes. We estimate the branching ratios of rare lepton flavor violating $B\to K(\pi )l_i^{-}{l}_j^{+}$ processes using the constrained leptoquark couplings. We also compute the forward-backward asymmetries and the lepton nonuniversality parameters of the LFV decays in the vector leptoquark model. Furthermore, we study the effect of vector leptoquark on the $(g-2{)}_{\mu }$ anomaly.

Taking advantage of the fact that the flavor of the neutrino in semileptonic $B$ decays $B\to D^{(*)}\tau \nu$ is not known, we show how a minimal set of higher-dimensional lepton flavor violating (LFV) operators can explain the $R(D^{(*)})$ anomalies and, as a spin-off, can give rise to the LFV decay of the Higgs boson, $h\to \mu \tau$. We also show how none but the minimal set of operators survive the present data.

Direct detection bounds are beginning to constrain a very simple model of weakly interacting dark matter—a Majorana fermion with a coupling to the $Z$ boson. In a particularly straightforward gauge-invariant realization, this coupling is introduced via a higher-dimensional operator. While attractive in its simplicity, this model generically induces a large $\rho$ parameter. An ultraviolet completion that avoids an overly large contribution to $\rho$ is the singlet-doublet model. We revisit this model, focusing on the Higgs blind spot region of parameter space where spin-independent interactions are absent. This model successfully reproduces dark matter with direct detection mediated by the $Z$ boson but whose cosmology may depend on additional couplings and states. Future direct detection experiments should effectively probe a significant portion of this parameter space, aside from a small coannihilating region. As such, $Z$-mediated thermal dark matter as realized in the singlet-doublet model represents an interesting target for future searches.

The QCD collinear factorization framework allows one to describe exclusive backward production of a $J/\psi$ meson in pion-nucleon collisions in terms of pion-to-nucleon transition distribution amplitudes. We calculate the scattering amplitude at the leading order in the strong coupling constant and estimate the cross section of this reaction in the backward kinematical region for a medium energy pion beam available at the J-Parc experimental facility.

Over the past years, the LHC experiments have reported experimental evidence for processes associated to photon-photon and photon-hadron interactions, showing their potential to investigate the production of low- and high-mass systems in exclusive events. In the particular case of the photoproduction of vector mesons, the experimental study of this final state is expected to shed light on the description of the QCD dynamics at small values of the Bjorken-$x$ variable. In this paper, we extend previous studies for the exclusive $J/\mathrm{\Psi }$ and $\mathrm{\Upsilon }$ photoproduction in $pp$ collisions based on the nonlinear QCD dynamics by performing a detailed study of the final-state distributions that can be measured experimentally at the LHC and at a future circular collider. Predictions for the rapidity and transverse momentum distributions of the vector mesons and of final-state dimuons are presented for $pp$ collisions at $\sqrt{s}=7$, 13, and 100 TeV.

We make a detailed study of the photoproduction mechanism of the doubly heavy flavored $B_c^{(*)}$ meson at the purposed Large Hadron Electron Collider (LHeC) within the framework of nonrelativistic QCD. In addition to the photoproduction mechanism via the gluon-induced channel $\gamma +g\to B_c^{(*)}+b+\overline{c}$, the extrinsic heavy quark mechanism via the two channels $\gamma +c\to B_c^{(*)}+b$ and $\gamma +\overline{b}\to B_c^{(*)}+\overline{c}$ has also been studied. Those two extrinsic channels are generally suppressed by the heavy quark distribution functions in the proton, which provide significant contributions in the low and intermediate $p_T$ region. A detailed comparison of those channels together with the theoretical uncertainties has been presented. By summing up all the mentioned photoproduction channels, we observe that about $(1.04_{-0.53}^{+0.90})\times 10^5$ $B_c$ and $(4.86_{-2.30}^{+3.72})\times 10^5$ $B_c^{*}$ events can be generated at the LHeC in one operation year with the proton-electron collision energy $\sqrt{S}=1.30\mathrm{TeV}$ and the luminosity $\mathcal{L}\simeq 10^{33}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$. Here the errors are for $m_c=1.50\pm 0.20$ and $m_b=4.9\pm 0.40\mathrm{GeV}$. Thus, in addition to the hadronic experiments, the LHeC shall provide another helpful platform for studying the $B_c^{(*)}$ meson properties, especially to test the extrinsic heavy quark mechanism.

We study the excited $B$ mesons’ contributions to the coupled-channel effects under the framework of the ${{}^{3}P}_0$ model for the bottomonium. Contrary to what has been widely accepted, the contributions of $P$ wave $B$ mesons are generally the largest, and to some extent, this result is independent of the potential parameters. We also push the calculation beyond $B(1P)$ and carefully analyze the contributions of $B(2S)$. A form factor is a key ingredient to suppress the contributions of $B(2S)$ for low lying bottomonia. However, this suppression mechanism is not efficient for highly excited bottomonia, such as $\mathrm{\Upsilon }(5S)$ and $\mathrm{\Upsilon }(6S)$. We give explanations why this difficulty happens to the ${{}^{3}P}_0$ model and suggest analyzing the flux-tube breaking model for the full calculation of coupled-channel effects.

Recent studies provide evidence that long-baseline (LBL) experiments are sensitive to the extra $CP$ phases involved with light sterile neutrinos, whose existence is suggested by several anomalous short-baseline (SBL) results. We show that, within the $3+1$ scheme, the combination of the existing SBL data with the LBL results coming from the two currently running experiments, $\mathrm{NO}\nu \mathrm{A}$ and T2K, enables us to simultaneously constrain two active-sterile mixing angles, ${\theta }_{14}$ and ${\theta }_{24}$, and two $CP$ phases, ${\delta }_{13}\equiv \delta$ and ${\delta }_{14}$, although the information on the second $CP$ phase is still weak. The two mixing angles are basically determined by the SBL data, while the two $CP$ phases are constrained by the LBL experiments, once the information coming from the SBL setups is taken into account. We also assess the robustness or fragility of the estimates of the standard 3-flavor parameters in the more general $3+1$ scheme. To this regard we find that (i) the indication of $CP$ violation found in the 3-flavor analyses persists also in the $3+1$ scheme, with ${\delta }_{13}\equiv \delta$ having still its best-fit value around $-\pi /2$, (ii) the 3-flavor weak hint in favor of the normal hierarchy becomes even less significant when sterile neutrinos come into play, (iii) the weak indication of nonmaximal ${\theta }_{23}$ (driven by $\mathrm{NO}\nu \mathrm{A}$ disappearance data) persists in the $3+1$ scheme, where maximal mixing is disfavored at almost the 90% C.L. in both normal and inverted mass hierarchy, and (iv) the preference in favor of one of the two octants of ${\theta }_{23}$ found in the 3-flavor framework (higher octant for inverted mass hierarchy) is completely washed out in the $3+1$ scheme.

We show that 11-dimensional supergravity in Euclidean signature admits an exact classical solution with isometry corresponding to a three-dimensional scale-invariant field theory without conformal invariance. We also construct the holographic renormalization group flow that connects the known UV conformal fixed point and the new scale-invariant but not conformal fixed point. In view of holography, the existence of such classical solutions suggests that the topologically twisted M2-brane gauge theory possesses a scale-invariant but not conformal phase.

In this paper, we consider a charged massive fermionic quantum field in the idealized cosmic string spacetime and in the presence of a magnetic field confined in a cylindrical tube of finite radius. Three distinct configurations for the magnetic fields are taken into account: (i) a cylindrical shell of radius $a$, (ii) a magnetic field proportional to $1/r$, and (iii) a constant magnetic field. In these three cases, the axis of the infinitely long tube of radius $a$ coincides with the cosmic string. Our main objectives in this paper are to analyze the fermionic condensate (FC) and the vacuum expectation value (VEV) of the fermionic energy-momentum tensor. In order to do that, we explicitly construct the complete set of normalized wave functions for each configuration of the magnetic field. We show that in the region outside the tube, the FC and the VEV of the energy-momentum tensor are decomposed into two parts: The first ones correspond to the zero-thickness magnetic flux contributions, and the second ones are induced by the nontrivial structure of the magnetic field, named core-induced contributions. The latter present specific forms depending on the magnetic field configuration considered. We also show that the VEV of the energy-momentum tensor is diagonal and obeys the conservation condition, and its trace is expressed in terms of the fermionic condensate. The zero-thickness contributions to the FC and VEV of the energy-momentum tensor depend only on the fractional part of the ration of the magnetic flux inside the tube by the quantum one. As to the core-induced contributions, they depend on the total magnetic flux inside the tube and, consequently, in general, are not a periodic function of the magnetic flux.

We analyze the dynamics of the intersecting $\mathrm{D}3\text{−}{\mathrm{D}3}^{\prime }$-brane system overlapping in $1+1$ dimensions, in a holographic treatment where $N$ D3 branes are manifested as anti–de Sitter Schwartzschild geometry, and the ${\mathrm{D}3}^{\prime }$ brane is treated as a probe. We extract the thermodynamic equation of state from the set of embedding solutions, and analyze the stability at the perturbative and the nonperturbative level. We review a systematic procedure to resolve local instabilities and multivaluedness in the equations of state based on classic ideas of convexity in the microcanonical ensemble. We then identify a runaway behavior which was not noticed previously for this system.

We study a static system of self-gravitating radiations confined in a sphere by using numerical and analytical calculations. Because of the scaling symmetry of radiations, most of the main properties of a solution can be represented as a segment of a solution curve on a plane of two-dimensional scale invariant variables. We define an “approximate horizon” (AH) from the analogy with an apparent horizon. Any solution curve contains a unique point that corresponds to the AH. A given solution is uniquely labeled by three parameters representing the solution curve, the size of the AH, and the sphere size, which are an alternative to the data at the outer boundary. Various geometrical properties including the existence of an AH and the behaviors around the center can be identified from the parameters. We additionally present an analytic solution of the radiations on the verge of forming a black hole. Analytic formulas for the central mass of the naked singularity are given.

We have a new observation that near horizon symmetry generators, corresponding to diffeomorphisms which leave the horizon structure invariant, satisfy noncommutative Heisenberg algebra. The results are valid for any null surfaces (which have Rindler structure in the near null surface limit) and in any spacetime dimensions. Using the Sugawara construction technique the central charge is identified. It is shown that the horizon entropy is consistent with the standard form of the Cardy formula. Therefore we feel that the noncommutative algebra might lead to quantum mechanics of horizon and also can probe into the microscopic description of entropy.

We consider a cosmology in which dark matter and a quintessence scalar field responsible for the acceleration of the Universe are allowed to interact. Allowing for both conformal and disformal couplings, we perform a global analysis of the constraints on our model using Hubble parameter measurements, baryon acoustic oscillation distance measurements, and a Supernovae Type Ia data set. We find that the additional disformal coupling relaxes the conformal coupling constraints. Moreover, we show that, at the background level, a disformal interaction within the dark sector is preferred to both $\mathrm{\Lambda }\mathrm{CDM}$ and uncoupled quintessence, hence favoring interacting dark energy.

Neutrinos propagating in dense astrophysical environments sustain nonlinear refractive effects due to neutrino-neutrino forward scattering. We study geometric phases in neutrino oscillations that arise out of cyclic evolution of the potential generated by these forward-scattering processes. We perform several calculations, exact and perturbative, that illustrate the robustness of such phases, and of geometric effects more broadly, in the flavor evolution of neutrinos. The scenarios we consider are highly idealized in order to make them analytically tractable, but they suggest the possible presence of complicated geometric effects in realistic astrophysical settings. We also point out that in the limit of extremely high neutrino densities, the nonlinear potential in three flavors naturally gives rise to non-Abelian geometric phases. This paper is intended to be accessible to neutrino experts and nonspecialists alike.

Astrophysical searches for gamma rays are one of the main strategies to probe the annihilation or decay of dark matter particles. We present a new class of distinct sub-GeV spectral features that generically appear in kinematical situations where the available center-of-mass energy in such processes is just above threshold to produce excited meson states. Using a Fisher forecast with realistic astrophysical backgrounds, we demonstrate that for upcoming experiments like e-ASTROGAM and ComPair these signals can turn out to be the smoking gun in the search for particle dark matter.