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### Strings

**I. Coordinator:**

- Heng-Yu Chen, Department of Physics, National Taiwan University

II. Core Members:

- Chong-Sun Chu (National Tsing-Hua University)
- Chiang-Mei Chen (National Central University)
- Yu-tin Huang (National Taiwan University)
- Wen-Yu Wen (Chung-Yuan Christian University)
- Yi Yang (National Chiao-Tung University)

III. **Research Themes of Core Members**

- Here I briey summarize the current research themes of some of the core members:

**Chiang-Mei Chen**- Black hole physics has accomplished a signicant devel- opment in the past decades. In particular, by applying the holographic principle, one can study the dual conformal eld theory (CFT) description for the near extremal black holes. In the past years, we have intensively studied the extremal charged black holes, focusing on the mechanism of pair production near the horizon. Our results provide a more deep understanding about the thermal properties for the Hawking radiation and Schwinger eect. Currently we are focusing to consider the Schwinger eects in non-extremal charged black holes. In such cases, it is almost impossible to obtain the exact solution to the eld equations. However, we were aware the mathematical concept of monodromy and its properties may be able to help us to solve our problem. The other development spotlights the phenomenological applications to, for example condensed matter physics, and superconductor, via the corresponding gravitation setup. We have already developed our own numerical code to analysis the inhomogeneous systems and are studying the temperature and junction length dependence of superconducting current in the Josephson junction. Moreover, our research on the quasi-local energy (conserved quantities) for gravitation has achieved remarkable progress. We have checked the fact that most well-known pseudo-tensors for gravitational energy are actually giving the same result in the leading order. Now we are focusing to compute the gravitational energy carried by the gravitational waves. This could be a very important test for all gravitational energy proposals, including ours.

**Chong-Sun Chu**- Boundary system occurs everywhere in Nature and there are often beautiful phenomena associated with the boundary. For example, the edge modes of topological materials, Casimir forces between conducting plates, Hall eects etc. However boundary system is usually more complicated since the presence of boundary breaks symmetry and so the system with boundary is often richer and display more interesting physics. It is therefore very use- ful to have new approach that allows one to perform powerful analysis of the system that is beyond the standard perturbation approach. Chong-Sun Chu and collaborators have developed and complete the formulation of AdS corre- spondence for boundary CFT (BCFT). Using the AdS/BCFT, he has obtained novel results on boundary Weyl anomaly . He has also looked at boundary energy momentum tensor and uncovered exact relations on Casimir eects in BCFT. These relations can also be proven exactly using eld theory, thus they provide a nontrivial check of the validity of the proposed AdS/BCFT duality. In this project, Chong-SUn plan to further analysis the holographic principle for boundary system.

**Yu-tin Huang**- In recent years we have gathered sucient understanding and computation power in bootstrapping CFT correlators and implementing unitarity constraints on higher dimension operators in an eective eld theory. An important arena where these two ideas converge is the string landscape. Any compactied string theory will admit a four-point massless string ampli- tude that is written as a world sheet integral, with its integrand given by a product of free bosons (representing the at space time) and compact 2D CFT (representing the compactied space). The 2D CFT is subject to a 2D bootstrap equations. On the other hand, the resulting string amplitude will have a natural alpha prime (or the compactied scale) expansion that yields the S-matrix for the eective eld theory in four-dimensions, which is subject to the recently developed unitarity bounds. Thus the solution space to both constraints \denes" the allowed string landscape in an on-shell way that is independent of the details of the compactication. In the next two years we aim to initiate preliminary investigation into setting up systematic approach to utilize both constraints. This topic will require much input from the CFT community and can provide model building guidelines that are of phenomenological interest.
**Wen-Yu Wen**- In recent years I have been working on dierent aspects of black hole physics. Black holes provide a natural laboratory for tests of quantum gravity and String theory. However, humongous many ways of compactication down to four dimensions may leave us with rich landscapes and complicated moduli, therefore various versions of quantum gravity. In the past, we have learnt thermal metric of various deformed Schwarzschild-like black holes, black holes in noncommutative space behaving like torsion gravity and remnants may survive by feeding on ubiquitous dark matters, and intimate triangular relation among weak gravity conjecture, hoop conjecture and generalized second law of thermodynamics. In the near future, we plan to examine eective eld theories of quantum gravity in String landscapes and their implication to black hole physics, in particular, resolution of information loss paradox and the ER=EPR conjecture.
**Yi Yang**- In the last few years, I mainly focus on the following two top- ics related to string theory. The rst is the holographic duality. We built a holographic QCD theory to predict the QCD phase diagram for connement- deconnement phase transition as well as the linear Regge behavior of the meson spectrum. We then use our model to study the equations of the state in QCD, especially for the speed of sound. Instead of the well known conformal limit c2 s ?1=3 at high temperature, we reveal two more universal quantities in various limits: c2 s ?(d

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**. Activities:**

- Weekly Strings Seminars: Every Friday 2:20pm at Department of Physics, National Taiwan University; Annual Strings Workshop: Expected to be held in November or earlier, with three to four days duration, at NCTS-Hsin-Chu.
**Brief Justications for the Planned A****ctivities:**- The regular weekly seminars involve both domestic and international speakers, which are essential research activities for theoretical physics. Such occasion allow Thematic Group researchers to exchange current research developments and ideas with international visitors, accelerate the existing and develop th future research projects. Furthermore these regular activities help to increase the visibility of local community, especially for junior people such as students and postdocs.
- The annual workshop represents the major event for our Focus group, we usually invite a number of well-known international visitors simultaneously to give sets of pedagogical lectures/seminars on current research topics in theoret- ical high energy physics. The aim is to provide the local researchers, especially junior people necessary introductions to embark research on various latest topics. Moreover, given the number of the excellent Taiwanese junior researchers at early postdoctoral and later PhD levels in theoretical high energy physics, we plan to involve them both as invited speakers, participants and potential organizers in this workshop. This will provide these early stage researchers a relaxing platform to discuss and collaborate with their peers, also benet the local community.

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**Expected Achievements:**

- We expect to continue to successful program in promoting the research from local high energy theory community, especially connect more with other neigh- boring countries such as Japan, South Korea, China and India, as well as newly emerging Thailand. Moreover, given the number of the excellent Taiwanese young researchers in our eld, we expect to plan more activities oriented around their research interests and collaboration needs.