146 research outputs found
Two-Loop Helicity Amplitudes for Quark-Gluon Scattering in QCD and Gluino-Gluon Scattering in Supersymmetric Yang-Mills Theory
We present the two-loop QCD helicity amplitudes for quark-gluon scattering,
and for quark-antiquark annihilation into two gluons. These amplitudes are
relevant for next-to-next-to-leading order corrections to (polarized) jet
production at hadron colliders. We give the results in the `t Hooft-Veltman and
four-dimensional helicity (FDH) variants of dimensional regularization. The
transition rules for converting the amplitudes between the different variants
are much more intricate than for the previously discussed case of gluon-gluon
scattering. Summing our two-loop expressions over helicities and colors, and
converting to conventional dimensional regularization, gives results in
complete agreement with those of Anastasiou, Glover, Oleari and Tejeda-Yeomans.
We describe the amplitudes for 2 to 2 scattering in pure N=1 supersymmetric
Yang-Mills theory, obtained from the QCD amplitudes by modifying the color
representation and multiplicities, and verify supersymmetry Ward identities in
the FDH scheme.Comment: 77 pages. v2: corrected errors in eqs. (3.7) and (3.8) for one-loop
assembly; remaining results unaffecte
The finite-temperature chiral transition in QCD with adjoint fermions
We study the nature of the finite-temperature chiral transition in QCD with
N_f light quarks in the adjoint representation (aQCD). Renormalization-group
arguments show that the transition can be continuous if a stable fixed point
exists in the renormalization-group flow of the corresponding three-dimensional
Phi^4 theory with a complex 2N_f x 2N_f symmetric matrix field and
symmetry-breaking pattern SU(2N_f)->SO(2N_f). This issue is investigated by
exploiting two three-dimensional perturbative approaches, the massless
minimal-subtraction scheme without epsilon expansion and a massive scheme in
which correlation functions are renormalized at zero momentum. We compute the
renormalization-group functions in the two schemes to five and six loops
respectively, and determine their large-order behavior.
The analyses of the series show the presence of a stable three-dimensional
fixed point characterized by the symmetry-breaking pattern SU(4)->SO(4). This
fixed point does not appear in an epsilon-expansion analysis and therefore does
not exist close to four dimensions. The finite-temperature chiral transition in
two-flavor aQCD can therefore be continuous; in this case its critical behavior
is determined by this new SU(4)/SO(4) universality class. One-flavor aQCD may
show a more complex phase diagram with two phase transitions. One of them, if
continuous, should belong to the O(3) vector universality class.Comment: 36 page
On the nature of the finite-temperature transition in QCD
We discuss the nature of the finite-temperature transition in QCD with N_f
massless flavors. Universality arguments show that a continuous (second-order)
transition must be related to a 3-D universality class characterized by a
complex N_f X N_f matrix order parameter and by the symmetry-breaking pattern
[SU(N_f)_L X SU(N_f)_R]/Z(N_f)_V -> SU(N_f)_V/Z(N_f)_V, or [U(N_f)_L X
U(N_f)_R]/U(1)_V -> U(N_f)_V/U(1)_V if the U(1)_A symmetry is effectively
restored at T_c. The existence of any of these universality classes requires
the presence of a stable fixed point in the corresponding 3-D Phi^4 theory with
the expected symmetry-breaking pattern. Otherwise, the transition is of first
order. In order to search for stable fixed points in these Phi^4 theories, we
exploit a 3-D perturbative approach in which physical quantities are expanded
in powers of appropriate renormalized quartic couplings. We compute the
corresponding Callan-Symanzik beta-functions to six loops. We also determine
the large-order behavior to further constrain the analysis. No stable fixed
point is found, except for N_f=2, corresponding to the symmetry-breaking
pattern [SU(2)_L X SU(2)_R]/Z(2)_V -> SU(2)_V/Z(2)_V equivalent to O(4) ->
O(3). Our results confirm and put on a firmer ground earlier analyses performed
close to four dimensions, based on first-order calculations in the framework of
the epsilon=4-d expansion. These results indicate that the finite-temperature
phase transition in QCD is of first order for N_f>2. A continuous transition is
allowed only for N_f=2. But, since the theory with symmetry-breaking pattern
[U(2)_L X U(2)_R]/U(1)_V -> U(2)_V/U(1)_V does not have stable fixed points,
the transition can be continuous only if the effective breaking of the U(1)_A
symmetry is sufficiently large.Comment: 30 pages, 3 figs, minor correction
Dynamic Scaling and Two-Dimensional High-Tc Superconductors
There has been ongoing debate over the critical behavior of two-dimensional
superconductors; in particular for high Tc superconductors. The conventional
view is that a Kosterlitz-Thouless-Berezinskii transition occurs as long as
finite size effects do not obscure the transition. However, there have been
recent suggestions that a different transition actually occurs which
incorporates aspects of both the dynamic scaling theory of Fisher, Fisher, and
Huse and the Kosterlitz-Thouless-Berezinskii transition. Of general interest is
that this modified transition apparently has a universal dynamic critical
exponent. Some have countered that this apparent universal behavior is rooted
in a newly proposed finite-size scaling theory; one that also incorporates
scaling and conventional two-dimensional theory. To investigate these issues we
study DC voltage versus current data of a 12 angstrom thick YBCO film. We find
that the newly proposed scaling theories have intrinsic flexibility that is
relevant to the analysis of the experiments. In particular, the data scale
according to the modified transition for arbitrarily defined critical
temperatures between 0 K and 19.5 K, and the temperature range of a successful
scaling collapse is related directly to the sensitivity of the measurement.
This implies that the apparent universal exponent is due to the intrinsic
flexibility rather than some real physical property. To address this intrinsic
flexibility, we propose a criterion which would give conclusive evidence for
phase transitions in two-dimensional superconductors. We conclude by reviewing
results to see if our criterion is satisfied.Comment: 14 page
Understanding service usersâ and therapistsâ experiences of pharmacological treatment for sexual preoccupation and/or hypersexuality in incarcerated sex offenders
This research comprises two qualitative studies understanding the experiences of 1) convicted sex offenders voluntarily receiving pharmacological treatment to reduce sexual preoccupation and 2) therapists working with these offenders. The studies form part of a research programme evaluating the use of pharmacological treatment with sexual offenders. In study one, semi-structured interviews were conducted with 13 sexual offenders receiving selective serotonin reuptake inhibitors (SSRIs). In study two, interviews were conducted with eight intervention staff with varying levels of experience of working with offenders taking anti-libidinals. Thematic analysis was used and in study one, two main themes emerged: (i) the impact of the pharmacological treatment on prisonersâ daily functioning; (ii) barriers to compliance/engagement. In study two, three main themes emerged: (i) offendersâ reluctance to engage with pharmacological treatment; (ii) challenges for therapists; (iii) pharmacology: âjust another piece of the puzzleâ. Findings are discussed in relation to practice and future research
Direct Reaction Measurements Using GODDESS
GODDESS is a coupling of the charged-particle detection system ORRUBA to the gamma-ray detector array Gammasphere. This coupling has been developed in order to facilitate the high-resolution measurement of direct reactions in normal and inverse kinematics with stable and radioactive beams. GODDESS has been commissioned using a beam of 134Xe at 10 MeV/A, in a campaign of stable beam measurements. The measurement demonstrates the capabilities of GODDESS under radioactive beam conditions, and provides the first data on the single-neutron states in 135Xe, including previously unobserved states based on the orbitals above the N=82 shell closure
Hens vary their vocal repertoire and structure when anticipating different types of reward
The vocalizations of nonhuman animals are considered potential indicators of motivational or internal state. In many species, different call types, and structural variation within call types, encode information about physical characteristics such as age or sex, or about variable traits such as motivation. Domestic chickens, Gallus gallus, have an elaborate vocal repertoire, enabling investigation into whether reward-related arousal is encoded within their call type and structure. Twelve hens were given a Pavlovian conditioning paradigm using sound cues to signal the availability of two food rewards (mealworms, normal food), one nonfood reward (a container of substrate suitable for dustbathing), and a sound-neutral event (sound cue, no reward). A muted-neutral treatment (no sound cue, no reward) provided a baseline for vocal behaviour. Sound cues preceded a 15 s anticipation period during which vocalizations were recorded. Hens produced a âFood callâ (previously defined in other studies) in anticipation of all rewards, including the nonfood reward. âFood callsâ and âFast clucksâ were more prevalent in anticipation of rewards, and most prevalent following the cue signalling the dustbathing substrate, suggesting that this reward induced the most arousal in hens. The peak frequency of âFood callsâ made in anticipation of the dustbathing substrate was significantly lower than those made in anticipation of food rewards, potentially reflecting differences in arousal. Vocalizations that reliably indicate hens' motivational state could be used as measures of welfare in on-farm assessment situations. Our study is the first to reveal variation in the frequency-related parameters of the âFood callâ in different contexts, and to show the prevalence of different call types in reward and nonreward contexts, which may have implications for welfare assessments
Population, Land Use and Deforestation in the Pan Amazon Basin: a Comparison of Brazil, Bolivia, Colombia, Ecuador, PerĂș and Venezuela
This paper discusses the linkages between population change, land use, and deforestation in the Amazon regions of Brazil, Bolivia, Colombia, Ecuador, PerĂș, and Venezuela. We begin with a brief discussion of theories of populationâenvironment linkages, and then focus on the case of deforestation in the PanAmazon. The core of the paper reviews available data on deforestation, population growth, migration and land use in order to see how well land cover change reflects demographic and agricultural change. The data indicate that population dynamics and net migration exhibit to deforestation in some states of the basin but not others. We then discuss other explanatory factors for deforestation, and find a close correspondence between land use and deforestation, which suggests that land use is loosely tied to demographic dynamics and mediates the influence of population on deforestation. We also consider national political economic contexts of Amazon change in the six countries, and find contrasting contexts, which also helps to explain the limited demographic-deforestation correspondence. The paper closes by noting general conclusions based on the data, topics in need of further research and recent policy proposals.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42720/1/10668_2003_Article_6977.pd
The criminal justice voluntary sector: concepts and an agenda for an emerging field
This is the peer reviewed version of the following article: Tomczak, P. & Buck, G. (2019). The criminal justice voluntary sector: concepts and an agenda for an emerging field. Howard Journal of Crime and Justice, 58(3), which has been published in final form at https://doi.org/10.1111/hojo.12326. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.Volunteers and voluntary organisations play significant roles pervading criminal justice. They are key actors, with unrecognised potential to shore up criminal justice and/or collaboratively reshape social justice. Unlike public and for-profit agents, criminal justice volunteers and voluntary organisations (CJVVOs) have been neglected by scholars. We call for analyses of diverse CJVVOs, in national and comparative contexts. We provide three categories to highlight distinctive organising auspices, which hold across criminal justice: statutory volunteers, quasi-statutory volunteers and voluntary organisations. The unknown implications of these different forms of non-state, non-profit justice involvement deserve far greater attention from academics, policymakers and practitioners
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