Search results for "singularity"
showing 10 items of 352 documents
Calculation of theO(? s 2 ) parity-violating structure functions in $$e^ + e^ - \to q\bar qg$$
1986
We calculate the two nonvanishingO(αs2) parity-violating structure functions that contribute to\(e^ + e^ - \xrightarrow{{\gamma ,Z}}q\bar qg\). We discuss how these can be measured. We work with massless quarks and gluons and use dimensional regularization to regularize ultra-violet and infrared singularities. We carefully discuss how to deal withγ5 in the dimensional regularization scheme when infrared singularities are present.
Study of the possible role of triangle singularities in ${B^ - }\, \to {D^{*0}}{\pi ^ - }{\pi ^0}\eta $ and ${B^ - }\, \to {D^{*0}}{\pi ^ - }{\pi ^ +…
2019
Studying the effects of triangle singularities in hadronic processes is of the utmost importance since they can originate peaks that may wrongfully be associated with resonances. In this work, the role of the triangle mechanism in the decays and is explored. Here, the singularity appears when B- decays into , K *0 decays into K + through pion emission, and K - K + fuse together forming either the a 0 (980) or f 0 (980) which then decays into π 0 η or π+ π – , respectively. As a result, the K * K + K - loop generates a peak in the invariant mass of π - a 0 or π - f 0 around 1420 MeV. The branching ratios that come from this peak are and , which are well within the measurable range. Thus, thi…
Deforming D-brane models on T6/(Z2×Z2M) orbifolds
2016
We review the stabilisation of complex structure moduli in Type IIA orientifolds, especially on with discrete torsion, via deformations of orbifold singularities. While D6-branes in SO(2N) and USp(2N) models always preserve supersymmetry and thus give rise to flat directions, in an exemplary Pati-Salam model with only U(N) gauge groups ten out of the 15 deformation moduli can be stabilised at the orbifold point.
The extensions of gravitational soliton solutions with real poles
1998
We analyse vacuum gravitational "soliton" solutions with real poles in the cosmological context. It is well known that these solutions contain singularities on certain null hypersurfaces. Using a Kasner seed solution, we demonstrate that these may contain thin sheets of null matter or may be simple coordinate singularities, and we describe a number of possible extensions through them.
Comments on the dispersion relation method to vector–vector interaction
2019
We study in detail the method proposed recently to study the vector-vector interaction using the $N/D$ method and dispersion relations, which concludes that, while for $J=0$, one finds bound states, in the case of $J=2$, where the interaction is also attractive and much stronger, no bound state is found. In that work, approximations are done for $N$ and $D$ and a subtracted dispersion relation for $D$ is used, with subtractions made up to a polynomial of second degree in $s-s_\mathrm{th}$, matching the expression to $1-VG$ at threshold. We study this in detail for the $\rho - \rho$ interaction and to see the convergence of the method we make an extra subtraction matching $1-VG$ at threshold…
Triangle singularity mechanism for the pp→π+d fusion reaction
2021
We develop a model for the $pp\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}d$ reaction based on the $pp\ensuremath{\rightarrow}\mathrm{\ensuremath{\Delta}}(1232)N$ transition followed by $\mathrm{\ensuremath{\Delta}}(1232)\ensuremath{\rightarrow}\ensuremath{\pi}{N}^{\ensuremath{'}}$ decay and posterior fusion of $N{N}^{\ensuremath{'}}$ to give the deuteron. We show that the triangle diagram depicting this process develops a triangle singularity leading to a large cross section of this reaction compared to ordinary fusion reactions. The results of the calculation also show that the process is largely dominated by the $pp$ system in $L=2$ and $S=0$, which transfers $J=2$ to the final ${\ensu…
Integrability of J f and 1∕J f
2013
In this chapter we study the optimal degree of integrability of J f and 1∕J f for mappings of finite distortion. As an application of our estimates we show that some sets are removable singularities for mappings with exponentially integrable distortion.
Finitely determined singularities of ruled surfaces in 3
2009
AbstractWe study local singularities of ruled surfaces in 3. We show that any map germ f : (2, 0) → (3, 0) with a simple singularity is -equivalent to a ruled surface. Moreover, we give a topological classification of -finitely determined singularities of ruled surfaces and show that there are just eleven topological classes.
Infrared singularities in one-loop amplitudes
2010
In this talk we discuss a purely numerical approach to next-to-leading order calculations in QCD. We present a simple formula, which provides a local infrared subtraction term for the integrand of a one-loop amplitude. In addition we briefly comment on local ultraviolet subtraction terms and on the required deformation of the contour of integration.
From stringy particle physics to moduli stabilisation and cosmology
2016
Intersecting D6-branes provide a geometrically intuitive road to stringy particle physics models, where D6-branes stuck at orbifold singularities can lead to the stabilisation of deformation moduli, and the QCD axion can arise from the open string sector in a very constrained way compared to pure field theory. We demonstrate this interplay of different physical features here through an explicit model.