Particle production in models with helicity-0 graviton ghost in de Sitter spacetime

We revisit the problem of the helicity-0 ghost mode of massive graviton in the de Sitter background. In general, the presence of a ghost particle, which has negative energy, drives the vacuum to be unstable through pair production of ghost particles and ordinary particles. In the case that the vacuum state preserves the de Sitter invariance, the number density created by the pair production inevitably diverges due to unsuppressed ultra-violet(UV) contributions. In such cases one can immediately conclude that the model is not viable. However, in the massive gravity theory we cannot construct a vacuum state which respects the de Sitter invariance. Therefore the presence of a ghost does not immediately mean the breakdown of the model. Explicitly estimating the number density and the energy density of particles created by the pair production of two conformal scalar particles and one helicity-0 ghost graviton, we find that these densities both diverge. However, since models with helicity-0 ghost graviton have no de Sitter invariant vacuum state, it is rather natural to consider a UV cutoff scale in the three-dimensional momentum space. Then, even if we take the cutoff scale as large as the Planck scale, the created number density and energy density are well suppressed. In many models the cutoff scale is smaller than the Planck scale. In such models the created number density and the energy density are negligiblly small as long as only the physics below the cutoff scale is concerned.Comment: 7 pages, 1 figur

No de Sitter invariant vacuum in massive gravity theory with ghost

In this letter we point out that the massive gravity theory with a graviton ghost mode in de Sitter background cannot possess a de Sitter invariant vacuum state. In order to avoid a negative norm state, we must associate the creation operator of the ghost mode with a negative-energy mode function instead of a positive-energy one as the mode function. Namely, we have to adopt a different procedure of quantization for a ghost. When a theory has a symmetry mixing a ghost mode with ordinary non-ghost modes, the choice of a ghost mode is not unique. However, quantization of a ghost is impossible without specifying a choice of ghost mode, which breaks the symmetry. For this reason, the vacuum state cannot respect the symmetry. In the massive gravity theory with a graviton ghost mode in de Sitter background, the ghost is the helicity-0 mode of the graviton. This ghost mode is mixed with the other helicity graviton modes under the action of de Sitter symmetry. Therefore, there is no de Sitter invariant vacuum in such models. This leads to an interesting possibility that non-covariant cutoff of the low energy effective theory may naturally arise. As a result, the instability due to the pair production of a ghost and normal non-ghost particles gets much milder and that the model may escape from being rejected.Comment: 5 page

Gauge invariance, massless modes and topology of gauge fields in multi-band superconductors

Multi-phase physics is a new physics of multi-gap superconductors. Multi-band superconductors exhibit many interesting and novel properties. We investigate the dynamics of the phase-difference mode and show that this mode yields a new excitation mode. The phase-difference mode is represented as an abelian vector field. There are massless modes when the number of gaps is greater than three and the Josephson term is frustrated. The fluctuation of phase-difference modes with non-trivial topology leads to the existence of a fractional-quantum flux vortex in a magnetic field. A superconductor with a fractional-quantum flux vortex is regarded as a topological superconductor with the integer Chern number.Comment: Proceedings of the 12th Asia and Pacific Physics Conference (2013

Bubbles in the Self-Accelerating Universe

We revisit the issue of the stability in the Dvali-Gabadadze-Porrati model, by considering the nucleation of bubbles of the conventional branch within the self-accelerating branch. We construct an instanton describing this process in the thin wall approximation. On one side of the bubble wall, the bulk consists of the exterior of the brane while on the other side it is the interior. The solution requires the presence of a 2-brane (the bubble wall) which induces the transition. However, we show that this instanton cannot be realized as the thin wall limit of any smooth solution. Once the bubble thickness is resolved, the equations of motion do not allow O(4) symmetric solutions joining the two branches. We conclude that the thin wall instanton is unphysical, and that one cannot have processes connecting the two branches, unless negative tension bubble walls are introduced. This also suggests that the self-accelerating branch does not decay into the conventional branch nucleating bubbles. We comment on other kinds of bubbles that could interpolate between the two branches.Comment: 8 pages, 5 figure

看護婦の精神保健問題に関する研究

We investigated the mental health problem (MHP) through the analyses of various responses on the questionnaires asked to 307 hospital nurses in Tokai-Hokuriku district to attain a deeper insight into the causative factors underlying onto MHPs. The main findings obtained from the responded 304 nurses are summarized as follows : 1) Among responded nurses, as much as 245 nurses (81%) complained of certain types of MHPs which were mostly born from job-related issues (a total of 77%) such as coping strategy, job performance and interpsersonal relationship, but in part from family-related issues such as education of chidren and marriage (14%). Accompanied with the MHD, one-fifth of these nurses also complained of either sign of phsyical or mental health dysfunction such as sleeplessness (25%), lack of appetite (20%) and feeling of depression (20%). 2) Although five views of personality (being optimistic, pessimistic, seirous minded, sociable and unsociable) were cited with almost the same rates (25% to 16%), optimistic nurses reproted less frequently MHPS than pessimistic ones. 3) Comparing the causative factors of MHPs based on the ages and length of nursing experience, a tendency was shown that younger nurses with insufficient experiences find them in a process of job performance, whereas older ones with adequate experiences find in family-related issues. 4) To improve physical and mental dysfunctions, sleeping, talking, listening to music and traveling were cited as major measures. However, it was shown that consultation with certain persons or specialty books is essential for nurses with MHPs to improve their situations. In light of these fidings, it is suggested that the most important and effective measure is the establishment of consultation systems in the hospitals to provide more timely and easierly the chances of consultation to nurses facing to these situations.病院に働く看護婦は様々なストレスに曝され, 様々な精神保健問題に悩まされていることはよく知られている.しかし, これらの問題を扱った研究はわが国ではあまり見られないそこで我々はこの問題を明らかにするためにこの研究を計画し, 307名の看護婦を対象にかれらが経験している精神保健問題を調べ, 以下のような結果を得た.1)調査した対象者の81%は何らかの精神保健問題を経験し, そのうち5人に1人は精神的問題を持ち, 不眠や食欲不振, 抑うつなどの精神的・身体的不調を感じていた.2)また, 殆どの看護婦は精神保健問題の原因は彼等の対処方法, 仕事の能力, 職場の対人関係, および家族の問題にあると思っていた.3)若く経験の浅い看護婦はその原因を仕事にあると考え, 年配の経験のある看護婦はその原因を子供の養育にあると考えていた.4)対象者の3人に2人は看護婦として大らか, 生真面目, 社交的などの望ましい性格傾向を持っていた.そして大らかな人ほど精神保健問題の経験も少なかった.5)対象者のとっている, 精神保健問題の主な対処方法は寝る, おしゃべりをする, 本を読む, 音楽を聞く, 旅行をするであった.6)これらのことを考えると, 看護婦の仕事に影響する様々な精神保健問題の解決に当たっては, 看護婦自身の努力もさることながら, 病院が看護婦が気軽に利用できる効果的なカウンセリング機構を創り, そのニーズに応えることが重要である

Sense of Self in Baby Chimpanzees

Philippe Rochat and his colleague tentatively proposed that young infants' propensity to engage in self-perception and systematic exploration of the perceptual consequences of their own action plays and is probably at the origin of an early sense of self: the ecological self. Rochat and Hespos (1997) reported that neonates discriminate between external and self-stimulation. Neonate tended to display significantly more rooting responses (i.e., head turn towards the stimulation with mouth open and tonguing) following external compared to self-stimulation. Rochat et al. (1998) also reported that 2-month-olds showed clear sign of modulation of their oral activity on the pacifier as a function of analog versus non-analog condition. Rochat and his colleague concluded that these observations are interpreted as evidence of self-exploration and the emergence of a sense of self-agency by 2-month-olds. We tried to replicate these findings in infant chimpanzees. We observed rooting responses of three baby chimpanzees in two condition, self-stimulation and external stimulation. In external stimulation condition, the index finger of the experimenter or small stick touched one of the infant's cheeks. In self-stimulation condition, the experimenter took infant's hand and touched his or her cheek with their fingers. In Rochat and Hespos, they recorded and analyzed several measures such as state, head movement, mouth activity and so on. How ever, we analyzed only mouth activities tentatively. We found infant chimpanzees tended to show more rooting responses following external stimulation compared to self-stimulation as well as human infants. We also carried out sucking experiment with two baby chimpanzees. The experimenter held the pacifier and put the artificial nipple into the infant's mouth. A session started when the infant take the nipple inside the his or her mouth. Auditory stimulus, which was a complex tone comprised of six harmonics with equal intensity, was given to the chimpanzee according to the test condition during their sucking. There were four test conditions and each condition consisted with three types of feedback as follows: 1) silent baseline, contingent, and steady, 2) contingent baseline, 1-sec delay, and 3-sec delay, 3) contingent baseline, 6-sec delay, and 12-sec delay, 4) contingent baseline, 1/2 efficiency, and 1/4 efficiency. In test 1, one infant chimpanzee showed decrease of the minimum pressure of sucking in the contingent condition. In test 2, one subject showed shorter intervals of sucking in 3-sec delay condition. This seems to be similar to human infant's. We may be able to postulate ecological self in baby chimpanzees according to the self-exploration. In test 3 and 4, we did not obtain any effects of stimulus conditions. Results of these studies. These studies were conducted as the parts of the chimpanzee development project in Primate Research Institute, Kyoto University, organized by Professor Tetsuro Matsuzawa