bsuˉdˉbs\bar u\bar d : A Promising Detectable Tetraquark

We propose to investigate a particle with four different flavors, $bs\bar u\bar d$, which is a promising detectable tetraquark state. Its $BK$ threshold, 5773 MeV, is 270 MeV higher than the $B_s\pi$ threshold of $bd\bar u\bar s$ and $bu\bar d\bar s$, leading to a large mass region to be stable. If the lowest-lying \bsud state exists below threshold, it can be definitely observed via the weak decay mode $J/\Psi K^-K^-\pi^+$, with the expectation of hundreds of events in the current LHCb data sample but rejecting backgrounds due to its long lifetime. This can be a benchmark of the existence of $X(5568)$ which is a partner of $bs\bar u\bar d$ under the flavor $SU(3)$ symmetry. If no signal is observed in this mode, it constrain the mass of the ground tetraquark state to be larger than the threshold. In the case above threshold, it can be detected via the strong decay mode $\overline B^0K^-$. The $cs\bar u\bar d$ state has similar features.Comment: 5 pages, 2 figures and 2 table

Quantum phase transition in a three-level atom-molecule system

We adopt a three-level bosonic model to investigate the quantum phase transition in an ultracold atom-molecule conversion system which includes one atomic mode and two molecular modes. Through thoroughly exploring the properties of energy level structure, fidelity, and adiabatical geometric phase, we confirm that the system exists a second-order phase transition from an atommolecule mixture phase to a pure molecule phase. We give the explicit expression of the critical point and obtain two scaling laws to characterize this transition. In particular we find that both the critical exponents and the behaviors of ground-state geometric phase change obviously in contrast to a similar two-level model. Our analytical calculations show that the ground-state geometric phase jumps from zero to ?pi/3 at the critical point. This discontinuous behavior has been checked by numerical simulations and it can be used to identify the phase transition in the system.Comment: 8 pages,8 figure

One-step deterministic polarization entanglement purification using spatial entanglement

We present a one-step deterministic entanglement purification protocol with linear optics and postselection. Compared with the Simon-Pan protocol (Phys. Rev. Lett. 89, 257901 (2002)), this one-step protocol has some advantages. First, it can get a maximally entangled pair with only one step, not only improve the fidelity of less-entangled photon pairs by performing the protocol repeatedly. Second, it works in a deterministic way, not a probabilistic one, which will reduce a great deal of entanglement resources. Third, it does not require the polarization state be entangled, only spatial entanglement is needed. Moreover, it is feasible with current techniques (Nature 423, 417 (2003)). All these advantages will make this one-step protocol more convenient than others in the applications in quantum communication.Comment: 5 pages, 1 figures. A negligible error about the density matrix \rho"_p in Eq. (9) is correcte

Fiscal, Monetary, and Reserve Requirement Policy in an Endogenous Growth with Financial Market Imperfections

A simple endogenous growth model is developed in a framework where informational imperfections in financial markets give rise to adverse selection as well as costly state verification problems and the government needs to intervene financial markets to monetize its deficits. In the model, adverse selection problem raises credit rationing and financial intermediaries arise endogenously due to costly state verification. Inflation is shown to influence the amount of credit rationing and economic growth. We then examine the effects of government fiscal and monetary policies on equilibrium inflation, the amount of credit rationing, and thus economic growth. Results show that multiple equilibria arise when the share of government deficits is relatively large. We also illustrate how the use of reserve requirement policy can eliminate high inflation equilibrium and enable the government to reduce the inflation rate. In sum, it is found that Tobin effect hold when there is no reserve requirement or it is not binding. However, if the reserve requirement is set too high, such a policy will raise the equilibrium inflation rate and reduce economic growth, leading to a violation of Tobin effect.

Photon Polarization in the b->s gamma processes in the Left-Right Symmetric Model

The circular-polarization of the photon in the radiative B decays is dominantly left-handed in the Standard Model (SM), but the right-handed polarization may be enhanced in some new physics models with right-handed currents, such as the Left-Right Symmetric Model (LRSM). In this article, we investigate how large this wrong polarization could be within the allowed parameter space of the LRSM. We show that in LRSM, the right-handed polarization of the photon in the $b\to s\gamma$ processes could be largely enhanced by the $W_L-W_R$ mixing contributions because of the helicity flip on the internal top quark line of the penguin diagrams and the enhancement by the CKM factor $V_{ts}^R/V_{ts}^L$. We discuss the sensitivity of the proposed methods to determine the $b\to s\gamma$ photon polarization to the LRSM as well as their complementary role compared to the direct search of right-handed charged gauge bosons at LHC.Comment: 30pages, 5 figures, published version; references adde

Weak Decays of Doubly Heavy Baryons: the 1/2→1/21/2\to 1/2 case

Very recently, the LHCb collaboration has observed in the final state $\Lambda_c^+ K^-\pi^+\pi^+$ a resonant structure that is identified as the doubly-charmed baryon $\Xi_{cc}^{++}$. Inspired by this observation, we investigate the weak decays of doubly heavy baryons $\Xi_{cc}^{++}$, $\Xi_{cc}^{+}$, $\Omega_{cc}^{+}$, $\Xi_{bc}^{(\prime)+}$, $\Xi_{bc}^{(\prime)0}$, $\Omega_{bc}^{(\prime)0}$, $\Xi_{bb}^{0}$, $\Xi_{bb}^{-}$ and $\Omega_{bb}^{-}$ and focus on the decays into spin $1/2$ baryons in this paper. At the quark level these decay processes are induced by the $c\to d/s$ or $b\to u/c$ transitions, and the two spectator quarks can be viewed as a scalar or axial vector diquark. We first derive the hadronic form factors for these transitions in the light-front approach and then apply them to predict the partial widths for the semi-leptonic and non-leptonic decays of doubly heavy baryons. We find that a number of decay channels are sizable and can be examined in future measurements at experimental facilities like LHC, Belle II and CEPC.Comment: 40 pages, 4 figures, to appear in EPJ