Radiative transition of negative to positive parity nucleon

We investigate the $N^{\ast}(1535)\rightarrow N\gamma$ transition in the framework of light cone QCD sum rules. In particular, using the most general form of the interpolating current for the nucleon as well as the distribution amplitudes of the photon, we calculate two transition form factors responsible for this channel and use them to evaluate the decay width and branching ratio of the transition under consideration. The result obtained for the branching fraction is in a good consistency with the experimental data.Comment: A typo has been correcte

QCD nature of dark energy at finite temperature: cosmological implications

The Veneziano ghost field has been proposed as an alternative source of dark energy whose energy density is consistent with the cosmological observations. In this model, the energy density of QCD ghost field is expressed in terms of QCD degrees of freedom at zero temperature. We extend this model to finite temperature to search the model predictions from late time to early universe. We depict the variations of QCD parameters entering the calculations, dark energy density, equation of state, Hubble and deceleration parameters on temperature from zero to a critical temperature. We compare our results with the observations and theoretical predictions existing at different eras. It is found that this model safely defines the universe from quark condensation up to now and its predictions are not in tension with those of the standard cosmology. The EoS parameter of dark energy is dynamical and evolves from $-1/3$ in the presence of radiation to $-1$ at late time. The finite temperature ghost dark energy predictions on the Hubble parameter well fit to those of $\Lambda$CDM and observations at late time.Comment: 10 Pages and 6 Figures. Some references were rearrange

Modifications on nucleon parameters at finite temperature

Taking into account the additional operators coming up at finite temperature, we investigate the mass and residue of the nucleon in the framework of thermal QCD sum rules. We observe that the mass and residue of the nucleon are initially insusceptible to increase of temperature, however after a certain temperature, they start to fall increasing the temperature.Comment: 12 Pages, 4 Figures and 1 Tabl

Positive and negative parity hyperons in nuclear medium

The effects of nuclear medium on the residue, mass and self energy of the positive and negative parity $\Sigma$, $\Lambda$ and $\Xi$ hyperons are investigated using the QCD sum rule method. In the calculations, the general interpolating currents of hyperons with an arbitrary mixing parameter are used. We compare the results obtained in medium with those of the vacuum and calculate the shifts in the corresponding parameters. It is found that the shifts on the residues in nuclear matter are over all positive for both the positive and negative parity hyperons, except for the positive parity $\Sigma$ hyperon that the shift is negative. The shifts on the masses of these baryons are obtained to be negative. The shifts on the residues and masses of negative parity states are large compared to those of positive parities. The maximum shift belongs to the residue of the negative parity $\Lambda$ hyperon. The vector self-energies gained by the positive parity baryons are large compared to the negative parities' vector self-energies. The maximum value of the vector self-energy belongs to the positive parity $\Sigma$ hyperon. The numerical values are compared with the existing predictions in the literature.Comment: 20 Pages, 9 Figures and 7 Table

Semileptonic Bq→Dq∗lνB_{q}\to D^{\ast}_{q}l\nu (q=s,d,u)(q=s, d, u) Decays in QCD Sum Rules

The form factors relevant to $B_{q}\to D^{\ast}_{q}(J^{P}=1^{-}) ell\nu$ $(q=s, d, u)$ decays are calculated in the framework of the three point QCD sum rules approach. The heavy quark effective theory prediction of the form factors as well as $1/m_{b}$ corrections to those form factors are obtained. A comparison of the results for the ratio of form factors at zero recoil limit and other values of $q^{2}$ with the predictions of the subleading Isgur-Wise form factor application for $B\to D^{\ast}\ell\nu$ is presented. The total decay width and branching ratio for these decays are also evaluated using the $q^2$ dependencies of these form factors. The results are in good agreement with the constituent quark meson model and existing experimental data. The $q=s$ case can also be detected at LHC in the near future.Comment: 28 Pages, 6 Figures and 9 Table

On the strong coupling N(∗)N(∗)πN^{(*)}N^{(*)}\pi

We study the strong vertices $N^*N\pi$, $N^*N^*\pi$ and $NN\pi$ in QCD, where $N^*$ denotes the negative parity $N (1535)$ state. We use the most general form of the interpolating currents to calculate the corresponding strong coupling constants. It is obtained that the coupling associated to $N^*N\pi$ vertex is strongly suppressed compared to those related to two other vertices. The strong coupling corresponding to $N^*N^*\pi$ is obtained to be roughly half of that of $NN\pi$ vertex. We compare the obtained results on $N^*N\pi$ and $NN\pi$ vertices with the existing predictions of other theoretical studies as well as those extracted from the experimental data.Comment: 15 Pages, 4 Figures and 3 Table

The masses and residues of doubly heavy spin--3/2 baryons

The masses and residues of the spin--3/2 doubly heavy baryons are calculated within the QCD sum rules method. A comparison of our predictions with those existing in the literature is also made.Comment: 11 Pages and 4 Table

Scalar and vector self-energies of heavy baryons in nuclear medium

The in-medium sum rules are employed to calculate the shifts in the mass and residue as well as the scalar and vector self-energies of the heavy $\Lambda_Q, \Sigma_Q$ and $\Xi_Q$ baryons, with Q being $b$ or $c$ quark. The maximum shift in mass due to nuclear matter belongs to the $\Sigma_c$ baryon and it is found to be $\Delta m_{\Sigma_{c}}=-936 ~ MeV$. In the case of residue, it is obtained that the residue of $\Sigma_b$ baryon is maximally affected by the nuclear medium with the shift $\Delta \lambda_{\Sigma_b} = -0.014 ~ GeV^3$. The scalar and vector self-energies are found to be $\Sigma^{S}_{\Lambda_b} = 653 ~ MeV$, $\Sigma^{S}_{\Sigma_b} = -614 ~ MeV$, $\Sigma^{S}_{\Xi_b} = -17 ~ MeV$, $\Sigma^{S}_{\Lambda_c} = 272 ~ MeV$, $\Sigma^{S}_{\Sigma_c} = -936 ~ MeV$, $\Sigma^{S}_{\Xi_c} = -5 ~ MeV$ and $\Sigma^{\nu}_{\Lambda_b} = 436 \pm 148 ~ MeV$, $\Sigma^{\nu}_{\Sigma_b} = 382 \pm 129 ~MeV$, $\Sigma^{\nu}_{\Xi_b} =15 \pm 5 ~ MeV$, $\Sigma^{\nu}_{\Lambda_c} = 151 \pm 45 ~ MeV$, $\Sigma^{\nu}_{\Sigma_c} = 486 \pm 144 ~ MeV$ and $\Sigma^{\nu}_{\Xi_c} = 1.391 \pm 0.529 ~ MeV$.Comment: 13 Pages, 11 Figures and 5 Table

Thermal behavior of the mass and residue of hyperons

We investigate the mass and residue of the $\Sigma$, $\Lambda$ and $\Xi$ hyperons at finite temperature in the framework of thermal QCD sum rules. In our calculation, we take into account the additional operators coming up at finite temperature. We find the temperature-dependent continuum threshold for each hyperon using the obtained sum rules for their mass and residue. The numerical results demonstrate that the mass and residue of the particles under consideration remain stable up to a certain temperature, after which they decrease by increasing the temperature.Comment: 25Pages, 6 Figures and 2 Table