Expanding running coupling effects in the hard Pomeron

We study QCD hard processes at scales of order k^2 > Lambda^2 in the limit in which the beta-function coefficient - b is taken to be small, but alphas(k) is kept fixed. The (nonperturbative) Pomeron is exponentially suppressed in this limit, making it possible to define purely perturbative high-energy Green's functions. The hard Pomeron exponent acquires diffusion and running coupling corrections which can be expanded in the b parameter and turn out to be dependent on the effective coupling b alphas^2 Y. We provide a general setup for this b-expansion and we calculate the first few terms both analytically and numerically.Comment: 36 pages, 15 figures, additional references adde

Indications of beta-adrenoceptor blockers in Takotsubo syndrome and theoretical reasons to prefer agents with vasodilating activity

Takotsubo syndrome (TTS) is estimated to account for 1–3% of all patients presenting with suspected ST-segment elevation myocardial infarction. A sudden surge in sympathetic nervous system is considered the cause of TTS. Nonetheless, no specific recommendations have been provided regarding β-blocking therapy. Apart from specific contra-indications (severe LV dysfunction, hypotension, bradycardia and corrected QT interval >500 ms), treatment with a β-blocker seems reasonable until full recovery of LV ejection fraction, though evidence is limited to a few animal studies, case reports or observational studies. In this review, we will reappraise the rationale for β-blocker therapy in TTS and speculate on the pathophysiologic basis for preferring non-selective agents with vasodilating activity over β1-selective drugs

BFKL at next-to-leading order

This is a summary of the contributions on the next-to-leading order corrections to the BFKL equation which were presented to the `Small-x and Diffraction' working group at the 1998 Durham Workshop on HERA Physics.Comment: 6 pages, 2 figure

NLO BFKL Equation, Running Coupling and Renormalization Scales

I examine the solution of the BFKL equation with NLO corrections relevant for deep inelastic scattering. Particular emphasis is placed on the part played by the running of the coupling. It is shown that the solution factorizes into a part describing the evolution in Q^2, and a constant part describing the input distribution. The latter is infrared dominated, being described by a coupling which grows as x decreases, and thus being contaminated by infrared renormalons. Hence, for this part we agree with previous assertions that predictive power breaks down for small enough x at any Q^2. However, the former is ultraviolet dominated, being described by a coupling which falls like 1/(\ln(Q^2/\Lambda^2) + A(\bar\alpha_s(Q^2)\ln(1/x))^1/2)with decreasing x, and thus is perturbatively calculable at all x. Therefore, although the BFKL equation is unable to predict the input for a structure function for small x, it is able to predict its evolution in Q^2, as we would expect from the factorization theory. The evolution at small x has no true powerlike behaviour due to the fall of the coupling, but does have significant differences from that predicted from a standard NLO in alpha_s treatment. Application of the resummed splitting functions with the appropriate coupling constant to an analysis of data, i.e. a global fit, is very successful.Comment: Tex file, including a modification of Harvmac, 46 pages, 8 figures as .ps files. Correction of typos, updating of references, very minor corrections to text and fig.

Rapidity-Separation Dependence and the Large Next-to-Leading Corrections to the BFKL Equation

Recent concerns about the very large next-to-leading logarithmic (NLL) corrections to the BFKL equation are addressed by the introduction of a physical rapidity-separation parameter $\Delta$. At the leading logarithm (LL) this parameter enforces the constraint that successive emitted gluons have a minimum separation in rapidity, $y_{i+1}-y_i>\Delta$. The most significant effect is to reduce the BFKL Pomeron intercept from the standard result as $\Delta$ is increased from 0 (standard BFKL). At NLL this $\Delta$-dependence is compensated by a modification of the BFKL kernel, such that the total dependence on $\Delta$ is formally next-to-next-to-leading logarithmic. In this formulation, as long as $\Delta\gtrsim2.2$ (for $\alpha_{s}=0.15$): (i) the NLL BFKL pomeron intercept is stable with respect to variations of $\Delta$, and (ii) the NLL correction is small compared to the LL result. Implications for the applicability of the BFKL resummation to phenomenology are considered.Comment: 16 pages, 3 figures, Late

Takotsubo is not a cardiomyopathy

Unraveling the mechanisms underlying Takotsubo (TTS) leads to question the current inclusion of the condition within the spectrum of cardiomyopathies. Indeed, the clinical presentation and pathophysiology of TTS clearly differ from cardiomyopathies, i.e. diseases of heart muscle unexplained by abnormal loading conditions or coronary artery disease, which cannot recover spontaneously and may cause sudden death often in minimally symptomatic individuals or result in a gradual deterioration in ventricular function and end-stage heart failure. Furthermore, the term 'cardiomyopathy' can no longer be applied when functional or morphologic abnormalities of the coronary arteries leading to acute myocardial ischemia are deemed responsible for left ventricular (LV) systolic dysfunction. After 27years of investigation, time has come to recognize that patients with TTS do suffer from severe myocardial ischemia and fulfill all criteria of acute coronary syndromes, i.e. acute chest pain, typical electrocardiographic changes, cardiac troponin rise, as well as LV wall motion abnormalities. Accordingly, we propose that TTS should be labeled as an acute 'syndrome' to be included more appropriately within the spectrum of ischemic heart disease. With regard to the term 'stress', it may imply that the catecholamine surge is essential to produce the typical transient myocardial injury. Thus, the terminology 'Takotsubo (stress) syndrome' would more accurately reflect recent advances in the pathophysiology

Bloch-Nordsieck Violation in Spontaneously Broken Abelian Theories

We point out that, in a spontaneously broken U(1) gauge theory, inclusive processes, whose primary particles are mass eigenstates that do not coincide with the gauge eigenstates, are not free of infrared logarithms. The charge mixing allowed by symmetry breaking and the ensuing Bloch-Nordsieck violation are here analyzed in a few relevant cases and in particular for processes initiated by longitudinal gauge bosons. Of particular interest is the example of weak hypercharge in the Standard Model where, in addition, left-right mixing effects arise in transversely polarized fermion beams.Comment: 4 pages, 1 figur

Charm Hadroproduction in kTk_T-Factorization Approach

We compare the theoretical status and the numerical predictions of two approaches for heavy quark production in the high energy hadron collisions, namely the conventional LO parton model with collinear approximation and $k_T$-factorization approach. The main assumptions used in the calculations are discussed. To extract the differences coming from the matrix elements we use very simple gluon structure function and fixed coupling. It is shown that the $k_T$-factorization approach calculated formally in LO and with Sudakov form factor accounts for many contributions related usually to NLO (and even NNLO) processes of the conventional parton modelComment: 17 pages, 8 figure