119095544
Final state interactions and new physics in B ---> pi K decays
Within the standard model, and if one assumes that soft rescattering effects are negligible, the $\mathrm{CP}$ asymmetry ${\mathcal{A}}_{\mathrm{CP}}^{\mathrm{dir}}{(B}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}K)$ is predicted to be very small and the ratio ${R=B(B}_{d}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{\mp}}{K}^{\ifmmode\pm\else\textpm\fi{}}{)/B(B}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}K)$ provides a bound on the angle $\ensuremath{\gamma}$ of the unitarity triangle, ${\mathrm{sin}}^{2}\ensuremath{\gamma}l~R.$ We estimate the corrections from soft rescattering effects using an approach based on Regge phenomenology, and find effects of order $10%$ with large uncertainties. In particular, we conclude that ${\mathcal{A}}_{\mathrm{CP}}^{\mathrm{dir}}\ensuremath{\sim}0.2$ and ${\mathrm{sin}}^{2}\ensuremath{\gamma}\ensuremath{\sim}1.2R$ could not be taken unambiguously to signal new physics. Using SU(3) relations, we suggest experimental tests that could constrain the size of the soft rescattering effects thus reducing the related uncertainty. Finally, we study the effect of various models of new physics on ${\mathcal{A}}_{\mathrm{CP}}^{\mathrm{dir}}$ and on $R.$
118687281
Hadronic D and D(s) Meson Decays
We provide a comprehensive review of hadronic decays of D and D_s mesons. We discuss current theoretical and experimental challenges and successes in understanding of hadronic transitions of those mesons. A brief overview of the theoretical and experimental tools are given before discussing the absolute branching fractions for D and D_s mesons. Cabibbo suppressed and rare hadronic decays are discussed and compared with theory before discussing our understanding of hadronic multibody decays.
14564633
CHARM MIXING IN THE STANDARD MODEL AND BEYOND
Quantum mechanical meson-antimeson oscillations are sensitive to heavy degrees of freedom which propagate in the underlying mixing amplitudes. Comparing observed meson mixing with predictions of the Standard Model (SM), modern experimental studies would be able to constrain models of New Physics (NP). Yet, extensive precission data from B-factories and the Tevatron collider show that the large SM mixing succesfully describes all available experimental data in Bd and Bs oscillations. The only flavor oscillation not yet observed is that of the charmed meson D, where SM mixing is very small and the NP component can stand out. This situation is an exact opposite to what happens in the B system, where B − B0 mixing measurements are used to constrain top quark couplings. Together with the one loop Standard Model effects NP effects can contribute to ∆C = 1 (decays) or ∆C = 2 (mixing) transitions. In the case of D −D0 mixing these operators generate contributions to the effective operators that change D state into D0 state, leading to the mass eigenstates |D1,2〉 = p|D〉 ± q|D〉, (1)
14759150
Heavy meson molecules in effective field theory
We consider the implications from the possibility that the recently observed state X(3872) is a meson-antimeson molecule. We write an effective Lagrangian consistent with the heavy-quark and chiral symmetries needed to describe X(3872). We explore the consequences of the assumption that X(3872) is a molecular bound state of D�0 and D0 mesons for the existence of bound states in the D0D0 and D�0D �0
35942201
Is B-->Xs gamma equal to b-->s gamma ? Spectator contributions to rare inclusive B decays.
In $B \to X_s \gamma $ there are perturbative $QCD$ corrections at order $\alpha_s$ not only to the single quark line process $ b \to s \gamma$ but also coming from a set of diagrams where the weak interaction vertex involves a gluon which interacts with the spectator quark in the B hadron. We discuss the impact of the full set of these diagrams. These can influence the decay rate and also the line shape of the photon spectrum as they favor a softer photon energy than does the pure spectator decay $b \to s \gamma$. A subset of these diagrams generate differences in the decay rates for charged and neutral B's , $B^+ \to X_s \gamma$ vs. $B^0 \to X_s \gamma$ which can be searched for experimentally, although our calculation indicates that the effect will be hard to observe. Bound state effects turn out to be required to give rise to spectator corrections to the decay rate at order $\alpha_s$. The resulting contribution to the total rate is rather small (of about $5 \% $ ), although the effect is somewhat larger on portions of the photon spectrum.
117901603
X(3872) in effective field theory
We consider the implications from the possibility that the recently observed state X(3872) is a meson‐antimeson molecule. We write an effective Lagrangian consistent with the heavy‐quark and chiral symmetries needed to describe X(3872) and study its properties.
11565526
Gravitational lensing of the x-ray background by clusters of galaxies
Gravitational lensing by clusters of galaxies affects the cosmic X-ray background (XRB) by altering the observed density and flux distribution of background X-ray sources. At faint detection flux thresholds, the resolved X-ray sources appear brighter and diluted, while the unresolved component of the XRB appears dimmer and more anisotropic, because of lensing. The diffuse X-ray intensity in the outer halos of clusters might be lower than the sky-averaged XRB, after the subtraction of resolved sources. Detection of the lensing signal with a wide-field X-ray telescope could probe the mass distribution of a cluster out to its virialization boundary. In particular, we show that the lensing signature imprinted on the resolved component of the XRB by the cluster A1689 should be difficult, but possible, to detect out to 8' at the 2-4 σ level, after 106 s of observation with the forthcoming Advanced X-Ray Astrophysics Facility (AXAF) satellite. The lensing signal is fairly insensitive to the lens redshift in the range 0.1 zl 0.6. The amplitude of the lensing signal is, however, sensitive to the faint-end slope of the number-flux relation for unresolved X-ray sources, and it can thus help constrain models of the XRB. A search for X-ray arcs or arclets could identify the fraction of all faint sources that originate from extended emission of distant galaxies. The probability for a 3 σ detection of an arclet that is stretched by a factor of approximately 3 after a 106 s observation of A1689 with AXAF is roughly comparable to the fraction of all background X-ray sources that have an intrinsic size of approximately 1''.
31215380
X-ray orbital modulations in intermediate polars
We present an analysis of 30 archival ASCA and RXTE X-ray observations of 16 intermediate polars to investigate the nature of their orbital modulation. We show that X-ray orbital modulation is widespread amongst these systems, but not ubiquitous as indicated by previous studies that included fewer objects. Only seven of the sixteen systems show a clearly statistically significant modulation depth whose amplitude decreases with increasing X-ray energy. Interpreting this as due to photoelectric absorption in material at the edge of an accretion disc would imply that such modulations are visible for all system inclination angles in excess of 60 degrees. However, it is also apparent that the presence of an X-ray orbital modulation can appear and disappear on a timescale of ∼years or months in an individual system. This may be evidence for the presence of a precessing, tilted accretion disc, as inferred in some low mass X-ray binaries.
73563531
Metastability of the false vacuum in a Higgs-seesaw model of dark energy
In a recently proposed Higgs-Seesaw model the observed scale of dark energy results from a metastable false vacuum energy associated with mixing of the standard model Higgs particle and a scalar associated with new physics at the GUT or Planck scale. Here we address the issue of how to ensure metastability of this state over cosmological time. We consider new tree-level operators, the presence of a thermal bath of hidden sector particles, and quantum corrections to the effective potential. We find that in the thermal scenario many additional light degrees of freedom are typically required unless coupling constants are somewhat fine-tuned. However quantum corrections arising from as few as one additional light scalar field can provide the requisite support. We also briefly consider implications of late-time vacuum decay for the perdurance of observed structures in the universe in this model.
15136851
Broad-band X-ray measurements of the black hole candidate XTE J1908+094
XTE J1908+094 is an X-ray transient that went into outburst in February 2002. After two months it reached a 2- 250 keV peak fl ux of 1t o 2 10 8 erg cm 2 s 1 . Circumstantial evidence points to an accreting galactic black hole as the origin of the X-radiation: pulsations nor thermonuclear flashes were detected that would identify a neutron star and the spectrum was unusually hard for a neutron star at the outburst onset. We report on BeppoSAX and RXTE All Sky Monitor observations of the broad-band spectrum of XTE J1908+094. The spectrum is consistent with a model consisting of a Comptonization component by a40 keV plasma, a multicolor accretion disk blackbody component with a temperature just below 1 keV and a broad emission line at about 6 keV. The spectrum is heavily absorbed by cold interstellar matter with an equivalent hydrogen column density of 2:5 10 22 cm 2 , which makes it dicult to study the black body component in detail. The black body component exhibits strong evolution about 6 weeks into the outburst. Two weeks later this is followed by a swift decay of the power law component. The broadness of the 6 keV feature may be due to relativistic broadening or Compton scattering of a narrow Fe-K line.
118707424
A new rare type of supernovae: hypervelocity stellar collisions at galactic centers
When a binary star system is tidally disrupted by a supermassive black hole at a galactic nucleus, one star is ejected at a high speed while the other remains in a tightly bound orbit around the black hole. The cluster of tightly bound stars builds over time, eventually creating a steady state in which the rate of collisions between these stars is similar to the rate of capturing new stars. A large fraction of the collisions occur near the periapsis of the orbits around the black hole, where the kinetic energies are sufficient to generate an explosive disruption of the two stars involved. The typical flare brightens for several days, with a peak luminosity that is comparable to the lower-luminosity end of known supernovae. The explosion lightcurve is followed by a longer flare due to accretion of ejected matter onto the black hole. Dedicated searches in the near universe could observe several such "collisional-supernovae" per year.