118425306
Two freeze-out model for the hadrons produced in the Relativistic Heavy-Ion Collisions
An expanding fireball model with two freeze-outs, which assumes that the chemical freeze-out occurs earlier at higher temperature and the thermal freeze-out occurs later at lower temperature, is developed and successfully applied to fit simultaneously the hadron ratios, transverse momentum spectra of measured hadrons and rapidity distribution of charged hadrons measured in Au+Au collision at 200 A·GeV by STAR, PHENIX and PHOBOS collaborations. The quality of all the fittings is very good and the resulting parameters are in agreement with published values.
122366381
Collective flow model for the pion transverse momentum spectra from relativistic nuclear collisions at CERN
The transverse momentum spectra for pions observed by WA80 and NA35 collaborations are analysed within a fireball model with collective isentropic expansion and a realistic freeze-out criterion. By varing the initial state of the fireball, an excellent fit to the data is achieved for the whole measured range ofPT. Slight differences in the data for the spectral slopes from central and pheripheral collisions originate in our model from the difference in the size of the fireball and in the number of participating nucleons in central and peripheral collisions. Using additional information from two-pion correlations, we can extrapolate our model back from the freeze-out point (determined from the spectra) to the initial state; we find that an initial energy density of 1.5–2GGeV/fm3 is sufficient to explain the data from central O+Au collisions at 200A GeV.
117725824
Dynamical Evolution and Particle Production in Relativistic Nuclear Collisions
We present an overview of the different stages in the dynamical evolution of relativistic nuclear collisions, from the entropy generating initial pre-equilibrium stage through the hydrodynamic expansion phase to particle freeze-out. We discuss the various theoretical models which have been applied to these different stages, and compare their predictions with the recent results from heavy-ion experiments at CERN and Brookhaven. Particular attention is given to the possible formation and subsequent hadronization of a quark-gluon plasma in these collisions. The observed strange particle abundancies are interpreted as an indication for chemical equilibration in nuclear collisions, and the particle momentum spectra are analyzed for signs of collective expansion flow.
119332767
Analysis of Low-Energy Pion Spectra
The transverse mass spectra and the rapidity distributions of $\pi^+$ and $\pi^-$ in Au-Au collisions at 2, 4, 6, and 8 GeV$\cdot$A by E895 collaboration are fitted using an elliptically expanding fireball model with the contribution from the resonance decays and the final state Coulomb interaction. The ratio of the total number of produced $\pi^-$ and $\pi^+$ is used to fit the data. The resulting freeze-out temperature is rather low($T_f < 60$ MeV) with large transverse flow and thus resonance contribution is very small. The difference in the shape of $m_t$ spectra of the oppositely charged pions are found to be due to the Coulomb interaction of the pions.
45880759
Strange matter lumps in the early Universe.
We study the stability of hot strange matter lumps formed in the early Universe. As the Universe cools below the hadronization temperature, these lumps normally become unstable against boiling. They can stabilize themselves against this process if their mass is sufficiently large to hold a hadronic crust by gravitational attraction. Our analysis improves on previous studies of the internal structure of such stable hot quark matter lumps with hadronic crust by correctly treating the constraints from chemical equilibrium of baryonic and electric charge between crust and core. Since the expansion rate of the early Universe is much faster than the cooling rate of the strange matter lumps, their internal structure is characterized by constant entropy per baryon. Our improved analysis confirms the earlier finding that such stable quark matter lumps require a mass well above the total mass inside the horizon.
121511469
The ϱ-peak in the dimuon spectrum as a clock for fireball lifetimes in relativistic nuclear collisions
Abstract We discuss the modification of the dipleton yield from vector mesons inside a nuclear fireball. We argue that the relative magnitude of the ϱ peak in the dilepton spectrum determines the lifetime of the hadron gas phase in nuclear collisions with an accuracy of about 1 fm/ c . We also find that the φ (ω + ϱ) ratio measured in the dimuon channel in 200 A GeV O + U and S + U collisions points towards a rather short-lived hadronic phase in these collisions.
11851576
A Nonperturbative Test of M2-Brane Theory
We discuss non-perturbative effects in the ABJM model due to monopole instantons. We begin by constructing the instanton solutions in the U(2) × U(2) model, explicitly, and computing the Euclidean action. The Wick-rotated Lagrangian is complex and its BPS monopole instantons are found to be a delicate version of the usual 't Hooft-Polyakov monopole solutions. They are generically 1/3 BPS but become 1/2 BPS at special locus in the moduli space of two M2-branes, yet each instanton carries eight fermionic zero modes, regardless of the vacuum choice. The low energy effective action induced by monopole instantons are quartic order in derivatives. The resulting vertices are nonperturbative in 1/k, as expected, but are rational functions of the vacuum moduli. We also analyze the system of two M2-branes in the supergravity framework and compute the higher order interactions via 11-dimensional supergraviton exchange. The comparison of the two shows that the instanton vertices are precisely reproduced by this M2-brane picture, supporting the proposal that the ABJM model describes multiple M2-branes.
119361427
Exploring the charged Higgs bosons in the left-right symmetric model
We explore constraints on the charged Higgs sector in the left-right symmetric model from the present experimental data. Because of the different Yukawa structure, the allowed parameter space of the charged Higgs boson in the LR model is different from that of the two Higgs doublet model. We find that the constraint from t{yields}bH{sup {+-}} decay at Tevatron is most significant, while B{yields}{tau}{nu} decay could provide no constraint on the LR model. Bounds from e{sup -}e{sup +}{yields}H{sup -}H{sup +} process at LEP are similar to those in the two Higgs doublet model.
14742265
APPROXIMATE FLAVOR SYMMETRIES AND SEESAW MECHANISM
We study the approximate flavor symmetries imposed on the lepton sector assuming seesaw mechanism as the neutrino mass structure. We apply the symmetry to various neutrino phenomenologies and obtain constraints on neutrino masses and mixings.
1928023
Probing anomalous right-handed top quark couplings in rare $B$ decays
We explore the anomalous right-handed $\bar{t}sW$ and $\bar{t}bW$ couplings using $ B \to X_s \gamma$ and $B \to X_s l^+ l^-$ decays induced by the flavour-changing penguin diagrams. The anomalous $\bar{t}sW$ coupling can yield 10% enhancement of the $B \to X_s l^+ l^-$ decay rate under the constraint from the present $B \to X_s \gamma$ data, while it does not affect the forward-backward asymmetry of the charged lepton. The allowed region for anomalous $\bar{t}bW$ coupling by the $ B \to X_s \gamma$ constraint is two-fold, the small value region and the large value region. Though the effect of the small anomalous coupling on the $B \to X_s l^+ l^-$ branching ratio is very little, it can yield a substantial chanhge for the forward-backward asymmetry.
53705874
BPS electromagnetic waves on giant gravitons
We find new 1/8-BPS giant graviton solutions in AdS5 × S5, carrying three angular momenta along S5, and investigate their properties. Especially, we show that nonzero worldvolume gauge fields are admitted preserving supersymmetry. These gauge field modes can be viewed as electromagnetic waves along the compact D3 brane, whose Poynting vector contributes to the BPS angular momenta. We also analyze the (nearly-)spherical giant gravitons with worldvolume gauge fields in detail. Expressing the S3 in Hopf fibration (S1 fibred over S2), the wave propagates along the S1 fiber.